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IB Chemistry Resonance, Delocalization of Ozone and Benzene
Citation preview
httplawrencekokblogspotcom
Prepared by Lawrence Kok
Tutorial on Resonance Delocalization and catalytic destruction of Ozone
Delocalization of electrons
Resonance structures ozone
resonance structure 1 resonance structure 2
resonance hybrid
Ozone3O
Resonance bull Describing delocalization of electrons within a moleculepolyatomic ion where bonding cannot be express by ONE single Lewis structurebullDelocalization of π bond ndash π electrons spread over more than 2 nucleibullπ electrons are sharedbullπ electrons spread ndash more stable
UV radiation
Ozone at stratosphere
strongest radiation
Delocalization of electrons
Resonance structures ozone
resonance structure 1 resonance structure 2
resonance hybrid
bull All bonds O-O are identical in length and strengthbull Hybrid of 2 resonance structuresbull NO O-O (single) or O=O (double) bonds foundbull Only O ----- O bondbull Intermediate in character bet single and double bond
bull Bond Order = 211
Ozone3O
Click here on video ozone
Resonance bull Describing delocalization of electrons within a moleculepolyatomic ion where bonding cannot be express by ONE single Lewis structurebullDelocalization of π bond ndash π electrons spread over more than 2 nucleibullπ electrons are sharedbullπ electrons spread ndash more stable
bull Pale blue gas polar dimagneticbull Oxidizing agentbull Potent respiratory hazard and pollutant at ground levelbull Beneficial prevent UV BC from reaching Earth surfacebull Highest ozone level in stratosphere (10 km and 50 km)
UV radiation
Ozone at stratosphere
strongest radiation
3O
FORMAL CHARGE (FC)
Formal ChargebullToolModel for comparing which Lewis structures is more acceptablebullTreats covalent bond with equal electron distribution no electronegativity differences bet atombullElectronegative atom has negative while least electronegative atom has positive formal charge
Formula formal charge
V - valence electrons of atom L ndash lone pair electronB ndash bonding electron molecule
Formal charge sulfur dioxide
formal charge for O
L +
formal charge for Oformal charge for O
L + L + L +
FORMAL CHARGE (FC)
Formal ChargebullToolModel for comparing which Lewis structures is more acceptablebullTreats covalent bond with equal electron distribution no electronegativity differences bet atombullElectronegative atom has negative while least electronegative atom has positive formal charge
Formula formal charge
V - valence electrons of atom L ndash lone pair electronB ndash bonding electron molecule
Formal charge sulfur dioxide
formal charge for O
V- Valence electron O = 6L- Lone pair electron O = 4B- Bonding electron O = 4
L +
FC = 6 ndash (4 +2) = 0
formal charge for O
V- Valence electron O = 6L- Lone pair electron O = 6B- Bonding electron O = 2
FC = 6 ndash (6+1) = -1
formal charge for O
V- Valence electron O = 6L - Lone pair electron O = 2B - Bonding electron O = 6
FC = 6 ndash (2+3) = +1
All resonance structure contribute to electronic structure Real structure is combination of themLowest formal charge (stable) contribute more than less stable structureSum of formal charges must be zero for neutral or equal to charge on ion
0+1
-1
L + L + L +
Ozone Good and Bad Good Side Bad Side
Ozone in Strastopherebull blocks UV B + C
Ozone in Troposphere act asbull Greenhouse gas
Ozone in ground level act as bullPollutant bullPhotochemical
Ozone Good and Bad Good Side Bad Side
Ozone in Strastopherebull blocks UV B + C
Ozone in Troposphere act asbull Greenhouse gas
Ozone in ground level act as bullPollutant bullPhotochemical
Click here on ozone depletion substances ODS (phaseout)
Why ozone able to absorb UV B and UV C
Breakdown of ozone ndash High UV radiation ndash Skin cancer - DNA mutation
Ozone depletion
UV Exposure
Ozone Hole
Ozone absorb UV radiation
Ozone absorb UV BC
O=O Double bond
O=O=OInter
mediate
Bond lengthpm 121 127
Bond enthalpykJ mol-1
498 364
Bond order 2 15
Dissociation by UV
lt242nm
lt330nm
Ozone weaker bondbullAbsorb UV AB(wavelength 330nm)
Bonding O2 and O3
Oxygen stronger bondbullAbsorb UV C (wavelength 230nm)
How ozone layer protect life on earth How Ozone
protect
Ozone absorb UV radiation
Ozone absorb UV BC
Ozone formation
O=O Double bond
O=O=OInter
mediate
Bond lengthpm 121 127
Bond enthalpykJ mol-1
498 364
Bond order 2 15
Dissociation by UV
lt242nm
lt330nm
Ozone weaker bondbullAbsorb UV AB(wavelength 330nm)
Bonding O2 and O3
Oxygen stronger bondbullAbsorb UV C (wavelength 230nm)
How ozone layer protect life on earth
Ozone Cycle
How Ozone
protect
Oxygen split by high UV to O (radical)
O radical combine to form ozone
1
2
3 Ozone (stratosphere) absorb UV BC
4Ozone reform again
Ozone createddestroyed by Chapman cycle
Oxygen reform again
Ozone absorb UV radiation
Ozone absorb UV BC
Ozone formation
O=O Double bond
O=O=OInter
mediate
Bond lengthpm 121 127
Bond enthalpykJ mol-1
498 364
Bond order 2 15
Dissociation by UV
lt242nm
lt330nm
Ozone weaker bondbullAbsorb UV AB(wavelength 330nm)
Bonding O2 and O3
Oxygen stronger bondbullAbsorb UV C (wavelength 230nm)
Free radical -reactive species with unpair electron
How ozone layer protect life on earth
Ozone Cycle
How Ozone
protect
Oxygen split by high UV to O (radical)
O radical combine to form ozone
1
2
3 Ozone (stratosphere) absorb UV BC
4Ozone reform again
Ozone cycle
Ozone createddestroyed by Chapman cycle
Oxygen reform again
Ozone absorb UV BC
CFC breaks down
How CFC breaks down
High UV BC
How CI radical destroy ozone
Catalytic destruction of ozone
Ozone Depleting Substances (ODS)
Carbon
Fluorine
Chlorine
Ozone absorb UV BC
CFC breaks down
How CFC breaks down
High UV BC
How CI radical destroy ozone
Catalytic destruction of ozone
Ozone Depleting Substances (ODS)
CI free radicals form
CImiddot react O3 form CIOmiddot radical
CIOmiddot react Omiddot form CImiddot radical again
Net eqn- ozone break down
Carbon
Fluorine
Chlorine
Ozone absorb UV BC
CFC breaks down
How CFC breaks down
High UV BC
How CI radical destroy ozone
Catalytic destruction of ozone
Ozone Depleting Substances (ODS)
How CFC destroys ozone
CI free radicals form
CImiddot react O3 form CIOmiddot radical
CIOmiddot react Omiddot form CImiddot radical again
Net eqn- ozone break down
Carbon
Fluorine
Chlorine
CI radical catalyzes again
Ozone absorb UV BC
How NO radical destroy ozone
Catalytic destruction of ozone
Ozone Depleting Substances (ODS)
Oxides of Nitrogen
Nitrogen Dioxide (NO2)
Nitrogen monoxide (nitric oxide NO)
Nitrous oxideN2O
Break down to form NO free radical (unpair electron)
+
Ozone absorb UV BC
NOx breaks down
How CFC breaks down
High UV BCHow NO radical destroy ozone
Catalytic destruction of ozone
Ozone Depleting Substances (ODS)
NO free radicals form
NO react O3 form NO2 radical
NO2 react O form NO radical again
Net eqn- ozone breaks down
Oxides of Nitrogen
Nitrogen Dioxide (NO2)
Nitrogen monoxide (nitric oxide NO)
Nitrous oxideN2O
Break down to form NO free radical (unpair electron)
NO NO2
NO2 NO + O2
+
Ozone absorb UV BC
NOx breaks down
How CFC breaks down
High UV BCHow NO radical destroy ozone
Catalytic destruction of ozone
Ozone Depleting Substances (ODS)
NO free radicals form
NO react O3 form NO2 radical
NO2 react O form NO radical again
Net eqn- ozone breaks down
Oxides of Nitrogen
Nitrogen Dioxide (NO2)
Nitrogen monoxide (nitric oxide NO)
Nitrous oxideN2O
Break down to form NO free radical (unpair electron)
NO NO2
NO2 NO + O2
Sources of NOx
Catalytic destruction of ozone
Ozone Depleting Substances (ODS)
Source of ODSbullHalogenated substancebullMan-made halocarbon refrigerant solvent propellantbullFoam-blowing agent (CFCs HCFCs freons halons)
Trichloroflouromethane CFC-11
Dichlorodifluoromethane CFC-12
Chlorodifluoromethane HCFC-22
Catalytic destruction of ozone
Ozone Depleting Substances (ODS)
Source of ODSbullHalogenated substancebullMan-made halocarbon refrigerant solvent propellantbullFoam-blowing agent (CFCs HCFCs freons halons)
CFCbullContain chlorine fluorine and carbon atomsbullExtremely stable with strong bonds long half lifebullStability allows CFC into the stratosphere bullHigh UV radiation reacts with CFCbullHigh UV photons breaks CFC (photochemical decomposition) bull Free Cl radicals form - destroying ozone
Trichloroflouromethane CFC-11
Dichlorodifluoromethane CFC-12
Chlorodifluoromethane HCFC-22
Why halogenate
d CFC used
Less harmful
Very harmful
Catalytic destruction of ozone
Ozone Depleting Substances (ODS)
Source of ODSbullHalogenated substancebullMan-made halocarbon refrigerant solvent propellantbullFoam-blowing agent (CFCs HCFCs freons halons)
Montreal Protocol bans CFC halon and ODS like carbon tetrachloride and trichloroethane
CFCbullContain chlorine fluorine and carbon atomsbullExtremely stable with strong bonds long half lifebullStability allows CFC into the stratosphere bullHigh UV radiation reacts with CFCbullHigh UV photons breaks CFC (photochemical decomposition) bull Free Cl radicals form - destroying ozone
Trichloroflouromethane CFC-11
Dichlorodifluoromethane CFC-12
Chlorodifluoromethane HCFC-22
Why halogenate
d CFC used
Less harmful
Very harmful
Why fluorinated is safer
Delocalization of electrons
Resonance bull Describing delocalization of electrons within a moleculepolyatomic ion where bonding cannot be express by ONE single Lewis structurebullDelocalization of π bond ndash π electrons spread over more than 2 nucleibullπ electrons are sharedbullπ electrons spread ndash more stable
Resonance structures benzene
Benzene6HC6
resonance structure 1 resonance structure 2
bull Unhybridised p orbitalbull Delocalization electrons above below planebull sp2 hybridization on carbon center
Delocalized electrons
Kekuleacute structure Cyclohexa- 135 triene
χ doublesingle bonds bet them
Benzene
Hexagonal planar
Kekule
Delocalization of electrons
Resonance bull Describing delocalization of electrons within a moleculepolyatomic ion where bonding cannot be express by ONE single Lewis structurebullDelocalization of π bond ndash π electrons spread over more than 2 nucleibullπ electrons are sharedbullπ electrons spread ndash more stable
Resonance structures benzene
Benzene6HC6
resonance structure 1 resonance structure 2
Resonance hybrid
bull All bonds C6H6 are identical in length strengthbull Hybrid of 2 resonance structuresbull No C-C (single) or C=C (double) bonds foundbull Only C ----- C bondbull Intermediate character bet singledouble bond
bull Bond Order =
bull Unhybridised p orbitalbull Delocalization electrons above below planebull sp2 hybridization on carbon center
15
Click here to view
Delocalized electrons
Kekuleacute structure Cyclohexa- 135 triene
χ doublesingle bonds bet them
Benzene
Hexagonal planar
Resonance Hybrid more stable than any of the resonance structure
Click here to view
Kekule
ResonanceDelocalization Energy
ΔH cyclohexene = -120kJmol-1
ΔH cyclohexa 13 diene = -240kJmol-1
ΔH cyclohexa 135 triene = -360kJmol-1
ΔH Benzene = -208kJmol-1
Enthalpy change hydrogenation
χ
helliphellip
bull Benzene lower in energy by 150kJbull More stable due to delocalization of π electrons
150kJ-150
3 Evidence for Benzene structure1
ResonanceDelocalization Energy
ΔH cyclohexene = -120kJmol-1
ΔH cyclohexa 13 diene = -240kJmol-1
ΔH cyclohexa 135 triene = -360kJmol-1
ΔH Benzene = -208kJmol-1
Enthalpy change hydrogenation
χ
helliphellip
bull Benzene lower in energy by 150kJbull More stable due to delocalization of π electrons
150kJ-150
C-CSingle bond
C=CDouble bond
C=CBenzene
Bond lengthpm 154 134 140
Bond enthalpykJmol-1
346 614 507
3 Evidence for Benzene structure1
2
bull X ray hit benzene crystalbull Interact with electron (electron density
map) bull X ray diffraction producedbull Bond length measured
X ray crystallography
NO singledouble bond detected
ResonanceDelocalization Energy
ΔH cyclohexene = -120kJmol-1
ΔH cyclohexa 13 diene = -240kJmol-1
ΔH cyclohexa 135 triene = -360kJmol-1
ΔH Benzene = -208kJmol-1
Enthalpy change hydrogenation
χ
helliphellip
bull Benzene lower in energy by 150kJbull More stable due to delocalization of π electrons
150kJ-150
C-CSingle bond
C=CDouble bond
C=CBenzene
Bond lengthpm 154 134 140
Bond enthalpykJmol-1
346 614 507
3 Evidence for Benzene structure1
2
Click here evidence against Kekule
bull X ray hit benzene crystalbull Interact with electron (electron density
map) bull X ray diffraction producedbull Bond length measured
X ray crystallography
NO singledouble bond detected
3 Addition reaction for unsaturated C=C
Addition reaction
Substitution reaction
NO double bond
Acknowledgements
Thanks to source of pictures and video used in this presentation
Thanks to Creative Commons for excellent contribution on licenseshttpspaceplacenasagovgreenhouseenhttpwwwozonedepletioninfoeducationpart3ozonesourceshtmlhttpcreativecommonsorglicenseshttpwwwciesinorgdocs011-462011-462htmlhttpwwwepmagazineorgstorage165benzene-evidenceaspx
Prepared by Lawrence Kok
Check out more video tutorials from my site and hope you enjoy this tutorialhttplawrencekokblogspotcom
Delocalization of electrons
Resonance structures ozone
resonance structure 1 resonance structure 2
resonance hybrid
Ozone3O
Resonance bull Describing delocalization of electrons within a moleculepolyatomic ion where bonding cannot be express by ONE single Lewis structurebullDelocalization of π bond ndash π electrons spread over more than 2 nucleibullπ electrons are sharedbullπ electrons spread ndash more stable
UV radiation
Ozone at stratosphere
strongest radiation
Delocalization of electrons
Resonance structures ozone
resonance structure 1 resonance structure 2
resonance hybrid
bull All bonds O-O are identical in length and strengthbull Hybrid of 2 resonance structuresbull NO O-O (single) or O=O (double) bonds foundbull Only O ----- O bondbull Intermediate in character bet single and double bond
bull Bond Order = 211
Ozone3O
Click here on video ozone
Resonance bull Describing delocalization of electrons within a moleculepolyatomic ion where bonding cannot be express by ONE single Lewis structurebullDelocalization of π bond ndash π electrons spread over more than 2 nucleibullπ electrons are sharedbullπ electrons spread ndash more stable
bull Pale blue gas polar dimagneticbull Oxidizing agentbull Potent respiratory hazard and pollutant at ground levelbull Beneficial prevent UV BC from reaching Earth surfacebull Highest ozone level in stratosphere (10 km and 50 km)
UV radiation
Ozone at stratosphere
strongest radiation
3O
FORMAL CHARGE (FC)
Formal ChargebullToolModel for comparing which Lewis structures is more acceptablebullTreats covalent bond with equal electron distribution no electronegativity differences bet atombullElectronegative atom has negative while least electronegative atom has positive formal charge
Formula formal charge
V - valence electrons of atom L ndash lone pair electronB ndash bonding electron molecule
Formal charge sulfur dioxide
formal charge for O
L +
formal charge for Oformal charge for O
L + L + L +
FORMAL CHARGE (FC)
Formal ChargebullToolModel for comparing which Lewis structures is more acceptablebullTreats covalent bond with equal electron distribution no electronegativity differences bet atombullElectronegative atom has negative while least electronegative atom has positive formal charge
Formula formal charge
V - valence electrons of atom L ndash lone pair electronB ndash bonding electron molecule
Formal charge sulfur dioxide
formal charge for O
V- Valence electron O = 6L- Lone pair electron O = 4B- Bonding electron O = 4
L +
FC = 6 ndash (4 +2) = 0
formal charge for O
V- Valence electron O = 6L- Lone pair electron O = 6B- Bonding electron O = 2
FC = 6 ndash (6+1) = -1
formal charge for O
V- Valence electron O = 6L - Lone pair electron O = 2B - Bonding electron O = 6
FC = 6 ndash (2+3) = +1
All resonance structure contribute to electronic structure Real structure is combination of themLowest formal charge (stable) contribute more than less stable structureSum of formal charges must be zero for neutral or equal to charge on ion
0+1
-1
L + L + L +
Ozone Good and Bad Good Side Bad Side
Ozone in Strastopherebull blocks UV B + C
Ozone in Troposphere act asbull Greenhouse gas
Ozone in ground level act as bullPollutant bullPhotochemical
Ozone Good and Bad Good Side Bad Side
Ozone in Strastopherebull blocks UV B + C
Ozone in Troposphere act asbull Greenhouse gas
Ozone in ground level act as bullPollutant bullPhotochemical
Click here on ozone depletion substances ODS (phaseout)
Why ozone able to absorb UV B and UV C
Breakdown of ozone ndash High UV radiation ndash Skin cancer - DNA mutation
Ozone depletion
UV Exposure
Ozone Hole
Ozone absorb UV radiation
Ozone absorb UV BC
O=O Double bond
O=O=OInter
mediate
Bond lengthpm 121 127
Bond enthalpykJ mol-1
498 364
Bond order 2 15
Dissociation by UV
lt242nm
lt330nm
Ozone weaker bondbullAbsorb UV AB(wavelength 330nm)
Bonding O2 and O3
Oxygen stronger bondbullAbsorb UV C (wavelength 230nm)
How ozone layer protect life on earth How Ozone
protect
Ozone absorb UV radiation
Ozone absorb UV BC
Ozone formation
O=O Double bond
O=O=OInter
mediate
Bond lengthpm 121 127
Bond enthalpykJ mol-1
498 364
Bond order 2 15
Dissociation by UV
lt242nm
lt330nm
Ozone weaker bondbullAbsorb UV AB(wavelength 330nm)
Bonding O2 and O3
Oxygen stronger bondbullAbsorb UV C (wavelength 230nm)
How ozone layer protect life on earth
Ozone Cycle
How Ozone
protect
Oxygen split by high UV to O (radical)
O radical combine to form ozone
1
2
3 Ozone (stratosphere) absorb UV BC
4Ozone reform again
Ozone createddestroyed by Chapman cycle
Oxygen reform again
Ozone absorb UV radiation
Ozone absorb UV BC
Ozone formation
O=O Double bond
O=O=OInter
mediate
Bond lengthpm 121 127
Bond enthalpykJ mol-1
498 364
Bond order 2 15
Dissociation by UV
lt242nm
lt330nm
Ozone weaker bondbullAbsorb UV AB(wavelength 330nm)
Bonding O2 and O3
Oxygen stronger bondbullAbsorb UV C (wavelength 230nm)
Free radical -reactive species with unpair electron
How ozone layer protect life on earth
Ozone Cycle
How Ozone
protect
Oxygen split by high UV to O (radical)
O radical combine to form ozone
1
2
3 Ozone (stratosphere) absorb UV BC
4Ozone reform again
Ozone cycle
Ozone createddestroyed by Chapman cycle
Oxygen reform again
Ozone absorb UV BC
CFC breaks down
How CFC breaks down
High UV BC
How CI radical destroy ozone
Catalytic destruction of ozone
Ozone Depleting Substances (ODS)
Carbon
Fluorine
Chlorine
Ozone absorb UV BC
CFC breaks down
How CFC breaks down
High UV BC
How CI radical destroy ozone
Catalytic destruction of ozone
Ozone Depleting Substances (ODS)
CI free radicals form
CImiddot react O3 form CIOmiddot radical
CIOmiddot react Omiddot form CImiddot radical again
Net eqn- ozone break down
Carbon
Fluorine
Chlorine
Ozone absorb UV BC
CFC breaks down
How CFC breaks down
High UV BC
How CI radical destroy ozone
Catalytic destruction of ozone
Ozone Depleting Substances (ODS)
How CFC destroys ozone
CI free radicals form
CImiddot react O3 form CIOmiddot radical
CIOmiddot react Omiddot form CImiddot radical again
Net eqn- ozone break down
Carbon
Fluorine
Chlorine
CI radical catalyzes again
Ozone absorb UV BC
How NO radical destroy ozone
Catalytic destruction of ozone
Ozone Depleting Substances (ODS)
Oxides of Nitrogen
Nitrogen Dioxide (NO2)
Nitrogen monoxide (nitric oxide NO)
Nitrous oxideN2O
Break down to form NO free radical (unpair electron)
+
Ozone absorb UV BC
NOx breaks down
How CFC breaks down
High UV BCHow NO radical destroy ozone
Catalytic destruction of ozone
Ozone Depleting Substances (ODS)
NO free radicals form
NO react O3 form NO2 radical
NO2 react O form NO radical again
Net eqn- ozone breaks down
Oxides of Nitrogen
Nitrogen Dioxide (NO2)
Nitrogen monoxide (nitric oxide NO)
Nitrous oxideN2O
Break down to form NO free radical (unpair electron)
NO NO2
NO2 NO + O2
+
Ozone absorb UV BC
NOx breaks down
How CFC breaks down
High UV BCHow NO radical destroy ozone
Catalytic destruction of ozone
Ozone Depleting Substances (ODS)
NO free radicals form
NO react O3 form NO2 radical
NO2 react O form NO radical again
Net eqn- ozone breaks down
Oxides of Nitrogen
Nitrogen Dioxide (NO2)
Nitrogen monoxide (nitric oxide NO)
Nitrous oxideN2O
Break down to form NO free radical (unpair electron)
NO NO2
NO2 NO + O2
Sources of NOx
Catalytic destruction of ozone
Ozone Depleting Substances (ODS)
Source of ODSbullHalogenated substancebullMan-made halocarbon refrigerant solvent propellantbullFoam-blowing agent (CFCs HCFCs freons halons)
Trichloroflouromethane CFC-11
Dichlorodifluoromethane CFC-12
Chlorodifluoromethane HCFC-22
Catalytic destruction of ozone
Ozone Depleting Substances (ODS)
Source of ODSbullHalogenated substancebullMan-made halocarbon refrigerant solvent propellantbullFoam-blowing agent (CFCs HCFCs freons halons)
CFCbullContain chlorine fluorine and carbon atomsbullExtremely stable with strong bonds long half lifebullStability allows CFC into the stratosphere bullHigh UV radiation reacts with CFCbullHigh UV photons breaks CFC (photochemical decomposition) bull Free Cl radicals form - destroying ozone
Trichloroflouromethane CFC-11
Dichlorodifluoromethane CFC-12
Chlorodifluoromethane HCFC-22
Why halogenate
d CFC used
Less harmful
Very harmful
Catalytic destruction of ozone
Ozone Depleting Substances (ODS)
Source of ODSbullHalogenated substancebullMan-made halocarbon refrigerant solvent propellantbullFoam-blowing agent (CFCs HCFCs freons halons)
Montreal Protocol bans CFC halon and ODS like carbon tetrachloride and trichloroethane
CFCbullContain chlorine fluorine and carbon atomsbullExtremely stable with strong bonds long half lifebullStability allows CFC into the stratosphere bullHigh UV radiation reacts with CFCbullHigh UV photons breaks CFC (photochemical decomposition) bull Free Cl radicals form - destroying ozone
Trichloroflouromethane CFC-11
Dichlorodifluoromethane CFC-12
Chlorodifluoromethane HCFC-22
Why halogenate
d CFC used
Less harmful
Very harmful
Why fluorinated is safer
Delocalization of electrons
Resonance bull Describing delocalization of electrons within a moleculepolyatomic ion where bonding cannot be express by ONE single Lewis structurebullDelocalization of π bond ndash π electrons spread over more than 2 nucleibullπ electrons are sharedbullπ electrons spread ndash more stable
Resonance structures benzene
Benzene6HC6
resonance structure 1 resonance structure 2
bull Unhybridised p orbitalbull Delocalization electrons above below planebull sp2 hybridization on carbon center
Delocalized electrons
Kekuleacute structure Cyclohexa- 135 triene
χ doublesingle bonds bet them
Benzene
Hexagonal planar
Kekule
Delocalization of electrons
Resonance bull Describing delocalization of electrons within a moleculepolyatomic ion where bonding cannot be express by ONE single Lewis structurebullDelocalization of π bond ndash π electrons spread over more than 2 nucleibullπ electrons are sharedbullπ electrons spread ndash more stable
Resonance structures benzene
Benzene6HC6
resonance structure 1 resonance structure 2
Resonance hybrid
bull All bonds C6H6 are identical in length strengthbull Hybrid of 2 resonance structuresbull No C-C (single) or C=C (double) bonds foundbull Only C ----- C bondbull Intermediate character bet singledouble bond
bull Bond Order =
bull Unhybridised p orbitalbull Delocalization electrons above below planebull sp2 hybridization on carbon center
15
Click here to view
Delocalized electrons
Kekuleacute structure Cyclohexa- 135 triene
χ doublesingle bonds bet them
Benzene
Hexagonal planar
Resonance Hybrid more stable than any of the resonance structure
Click here to view
Kekule
ResonanceDelocalization Energy
ΔH cyclohexene = -120kJmol-1
ΔH cyclohexa 13 diene = -240kJmol-1
ΔH cyclohexa 135 triene = -360kJmol-1
ΔH Benzene = -208kJmol-1
Enthalpy change hydrogenation
χ
helliphellip
bull Benzene lower in energy by 150kJbull More stable due to delocalization of π electrons
150kJ-150
3 Evidence for Benzene structure1
ResonanceDelocalization Energy
ΔH cyclohexene = -120kJmol-1
ΔH cyclohexa 13 diene = -240kJmol-1
ΔH cyclohexa 135 triene = -360kJmol-1
ΔH Benzene = -208kJmol-1
Enthalpy change hydrogenation
χ
helliphellip
bull Benzene lower in energy by 150kJbull More stable due to delocalization of π electrons
150kJ-150
C-CSingle bond
C=CDouble bond
C=CBenzene
Bond lengthpm 154 134 140
Bond enthalpykJmol-1
346 614 507
3 Evidence for Benzene structure1
2
bull X ray hit benzene crystalbull Interact with electron (electron density
map) bull X ray diffraction producedbull Bond length measured
X ray crystallography
NO singledouble bond detected
ResonanceDelocalization Energy
ΔH cyclohexene = -120kJmol-1
ΔH cyclohexa 13 diene = -240kJmol-1
ΔH cyclohexa 135 triene = -360kJmol-1
ΔH Benzene = -208kJmol-1
Enthalpy change hydrogenation
χ
helliphellip
bull Benzene lower in energy by 150kJbull More stable due to delocalization of π electrons
150kJ-150
C-CSingle bond
C=CDouble bond
C=CBenzene
Bond lengthpm 154 134 140
Bond enthalpykJmol-1
346 614 507
3 Evidence for Benzene structure1
2
Click here evidence against Kekule
bull X ray hit benzene crystalbull Interact with electron (electron density
map) bull X ray diffraction producedbull Bond length measured
X ray crystallography
NO singledouble bond detected
3 Addition reaction for unsaturated C=C
Addition reaction
Substitution reaction
NO double bond
Acknowledgements
Thanks to source of pictures and video used in this presentation
Thanks to Creative Commons for excellent contribution on licenseshttpspaceplacenasagovgreenhouseenhttpwwwozonedepletioninfoeducationpart3ozonesourceshtmlhttpcreativecommonsorglicenseshttpwwwciesinorgdocs011-462011-462htmlhttpwwwepmagazineorgstorage165benzene-evidenceaspx
Prepared by Lawrence Kok
Check out more video tutorials from my site and hope you enjoy this tutorialhttplawrencekokblogspotcom
Delocalization of electrons
Resonance structures ozone
resonance structure 1 resonance structure 2
resonance hybrid
bull All bonds O-O are identical in length and strengthbull Hybrid of 2 resonance structuresbull NO O-O (single) or O=O (double) bonds foundbull Only O ----- O bondbull Intermediate in character bet single and double bond
bull Bond Order = 211
Ozone3O
Click here on video ozone
Resonance bull Describing delocalization of electrons within a moleculepolyatomic ion where bonding cannot be express by ONE single Lewis structurebullDelocalization of π bond ndash π electrons spread over more than 2 nucleibullπ electrons are sharedbullπ electrons spread ndash more stable
bull Pale blue gas polar dimagneticbull Oxidizing agentbull Potent respiratory hazard and pollutant at ground levelbull Beneficial prevent UV BC from reaching Earth surfacebull Highest ozone level in stratosphere (10 km and 50 km)
UV radiation
Ozone at stratosphere
strongest radiation
3O
FORMAL CHARGE (FC)
Formal ChargebullToolModel for comparing which Lewis structures is more acceptablebullTreats covalent bond with equal electron distribution no electronegativity differences bet atombullElectronegative atom has negative while least electronegative atom has positive formal charge
Formula formal charge
V - valence electrons of atom L ndash lone pair electronB ndash bonding electron molecule
Formal charge sulfur dioxide
formal charge for O
L +
formal charge for Oformal charge for O
L + L + L +
FORMAL CHARGE (FC)
Formal ChargebullToolModel for comparing which Lewis structures is more acceptablebullTreats covalent bond with equal electron distribution no electronegativity differences bet atombullElectronegative atom has negative while least electronegative atom has positive formal charge
Formula formal charge
V - valence electrons of atom L ndash lone pair electronB ndash bonding electron molecule
Formal charge sulfur dioxide
formal charge for O
V- Valence electron O = 6L- Lone pair electron O = 4B- Bonding electron O = 4
L +
FC = 6 ndash (4 +2) = 0
formal charge for O
V- Valence electron O = 6L- Lone pair electron O = 6B- Bonding electron O = 2
FC = 6 ndash (6+1) = -1
formal charge for O
V- Valence electron O = 6L - Lone pair electron O = 2B - Bonding electron O = 6
FC = 6 ndash (2+3) = +1
All resonance structure contribute to electronic structure Real structure is combination of themLowest formal charge (stable) contribute more than less stable structureSum of formal charges must be zero for neutral or equal to charge on ion
0+1
-1
L + L + L +
Ozone Good and Bad Good Side Bad Side
Ozone in Strastopherebull blocks UV B + C
Ozone in Troposphere act asbull Greenhouse gas
Ozone in ground level act as bullPollutant bullPhotochemical
Ozone Good and Bad Good Side Bad Side
Ozone in Strastopherebull blocks UV B + C
Ozone in Troposphere act asbull Greenhouse gas
Ozone in ground level act as bullPollutant bullPhotochemical
Click here on ozone depletion substances ODS (phaseout)
Why ozone able to absorb UV B and UV C
Breakdown of ozone ndash High UV radiation ndash Skin cancer - DNA mutation
Ozone depletion
UV Exposure
Ozone Hole
Ozone absorb UV radiation
Ozone absorb UV BC
O=O Double bond
O=O=OInter
mediate
Bond lengthpm 121 127
Bond enthalpykJ mol-1
498 364
Bond order 2 15
Dissociation by UV
lt242nm
lt330nm
Ozone weaker bondbullAbsorb UV AB(wavelength 330nm)
Bonding O2 and O3
Oxygen stronger bondbullAbsorb UV C (wavelength 230nm)
How ozone layer protect life on earth How Ozone
protect
Ozone absorb UV radiation
Ozone absorb UV BC
Ozone formation
O=O Double bond
O=O=OInter
mediate
Bond lengthpm 121 127
Bond enthalpykJ mol-1
498 364
Bond order 2 15
Dissociation by UV
lt242nm
lt330nm
Ozone weaker bondbullAbsorb UV AB(wavelength 330nm)
Bonding O2 and O3
Oxygen stronger bondbullAbsorb UV C (wavelength 230nm)
How ozone layer protect life on earth
Ozone Cycle
How Ozone
protect
Oxygen split by high UV to O (radical)
O radical combine to form ozone
1
2
3 Ozone (stratosphere) absorb UV BC
4Ozone reform again
Ozone createddestroyed by Chapman cycle
Oxygen reform again
Ozone absorb UV radiation
Ozone absorb UV BC
Ozone formation
O=O Double bond
O=O=OInter
mediate
Bond lengthpm 121 127
Bond enthalpykJ mol-1
498 364
Bond order 2 15
Dissociation by UV
lt242nm
lt330nm
Ozone weaker bondbullAbsorb UV AB(wavelength 330nm)
Bonding O2 and O3
Oxygen stronger bondbullAbsorb UV C (wavelength 230nm)
Free radical -reactive species with unpair electron
How ozone layer protect life on earth
Ozone Cycle
How Ozone
protect
Oxygen split by high UV to O (radical)
O radical combine to form ozone
1
2
3 Ozone (stratosphere) absorb UV BC
4Ozone reform again
Ozone cycle
Ozone createddestroyed by Chapman cycle
Oxygen reform again
Ozone absorb UV BC
CFC breaks down
How CFC breaks down
High UV BC
How CI radical destroy ozone
Catalytic destruction of ozone
Ozone Depleting Substances (ODS)
Carbon
Fluorine
Chlorine
Ozone absorb UV BC
CFC breaks down
How CFC breaks down
High UV BC
How CI radical destroy ozone
Catalytic destruction of ozone
Ozone Depleting Substances (ODS)
CI free radicals form
CImiddot react O3 form CIOmiddot radical
CIOmiddot react Omiddot form CImiddot radical again
Net eqn- ozone break down
Carbon
Fluorine
Chlorine
Ozone absorb UV BC
CFC breaks down
How CFC breaks down
High UV BC
How CI radical destroy ozone
Catalytic destruction of ozone
Ozone Depleting Substances (ODS)
How CFC destroys ozone
CI free radicals form
CImiddot react O3 form CIOmiddot radical
CIOmiddot react Omiddot form CImiddot radical again
Net eqn- ozone break down
Carbon
Fluorine
Chlorine
CI radical catalyzes again
Ozone absorb UV BC
How NO radical destroy ozone
Catalytic destruction of ozone
Ozone Depleting Substances (ODS)
Oxides of Nitrogen
Nitrogen Dioxide (NO2)
Nitrogen monoxide (nitric oxide NO)
Nitrous oxideN2O
Break down to form NO free radical (unpair electron)
+
Ozone absorb UV BC
NOx breaks down
How CFC breaks down
High UV BCHow NO radical destroy ozone
Catalytic destruction of ozone
Ozone Depleting Substances (ODS)
NO free radicals form
NO react O3 form NO2 radical
NO2 react O form NO radical again
Net eqn- ozone breaks down
Oxides of Nitrogen
Nitrogen Dioxide (NO2)
Nitrogen monoxide (nitric oxide NO)
Nitrous oxideN2O
Break down to form NO free radical (unpair electron)
NO NO2
NO2 NO + O2
+
Ozone absorb UV BC
NOx breaks down
How CFC breaks down
High UV BCHow NO radical destroy ozone
Catalytic destruction of ozone
Ozone Depleting Substances (ODS)
NO free radicals form
NO react O3 form NO2 radical
NO2 react O form NO radical again
Net eqn- ozone breaks down
Oxides of Nitrogen
Nitrogen Dioxide (NO2)
Nitrogen monoxide (nitric oxide NO)
Nitrous oxideN2O
Break down to form NO free radical (unpair electron)
NO NO2
NO2 NO + O2
Sources of NOx
Catalytic destruction of ozone
Ozone Depleting Substances (ODS)
Source of ODSbullHalogenated substancebullMan-made halocarbon refrigerant solvent propellantbullFoam-blowing agent (CFCs HCFCs freons halons)
Trichloroflouromethane CFC-11
Dichlorodifluoromethane CFC-12
Chlorodifluoromethane HCFC-22
Catalytic destruction of ozone
Ozone Depleting Substances (ODS)
Source of ODSbullHalogenated substancebullMan-made halocarbon refrigerant solvent propellantbullFoam-blowing agent (CFCs HCFCs freons halons)
CFCbullContain chlorine fluorine and carbon atomsbullExtremely stable with strong bonds long half lifebullStability allows CFC into the stratosphere bullHigh UV radiation reacts with CFCbullHigh UV photons breaks CFC (photochemical decomposition) bull Free Cl radicals form - destroying ozone
Trichloroflouromethane CFC-11
Dichlorodifluoromethane CFC-12
Chlorodifluoromethane HCFC-22
Why halogenate
d CFC used
Less harmful
Very harmful
Catalytic destruction of ozone
Ozone Depleting Substances (ODS)
Source of ODSbullHalogenated substancebullMan-made halocarbon refrigerant solvent propellantbullFoam-blowing agent (CFCs HCFCs freons halons)
Montreal Protocol bans CFC halon and ODS like carbon tetrachloride and trichloroethane
CFCbullContain chlorine fluorine and carbon atomsbullExtremely stable with strong bonds long half lifebullStability allows CFC into the stratosphere bullHigh UV radiation reacts with CFCbullHigh UV photons breaks CFC (photochemical decomposition) bull Free Cl radicals form - destroying ozone
Trichloroflouromethane CFC-11
Dichlorodifluoromethane CFC-12
Chlorodifluoromethane HCFC-22
Why halogenate
d CFC used
Less harmful
Very harmful
Why fluorinated is safer
Delocalization of electrons
Resonance bull Describing delocalization of electrons within a moleculepolyatomic ion where bonding cannot be express by ONE single Lewis structurebullDelocalization of π bond ndash π electrons spread over more than 2 nucleibullπ electrons are sharedbullπ electrons spread ndash more stable
Resonance structures benzene
Benzene6HC6
resonance structure 1 resonance structure 2
bull Unhybridised p orbitalbull Delocalization electrons above below planebull sp2 hybridization on carbon center
Delocalized electrons
Kekuleacute structure Cyclohexa- 135 triene
χ doublesingle bonds bet them
Benzene
Hexagonal planar
Kekule
Delocalization of electrons
Resonance bull Describing delocalization of electrons within a moleculepolyatomic ion where bonding cannot be express by ONE single Lewis structurebullDelocalization of π bond ndash π electrons spread over more than 2 nucleibullπ electrons are sharedbullπ electrons spread ndash more stable
Resonance structures benzene
Benzene6HC6
resonance structure 1 resonance structure 2
Resonance hybrid
bull All bonds C6H6 are identical in length strengthbull Hybrid of 2 resonance structuresbull No C-C (single) or C=C (double) bonds foundbull Only C ----- C bondbull Intermediate character bet singledouble bond
bull Bond Order =
bull Unhybridised p orbitalbull Delocalization electrons above below planebull sp2 hybridization on carbon center
15
Click here to view
Delocalized electrons
Kekuleacute structure Cyclohexa- 135 triene
χ doublesingle bonds bet them
Benzene
Hexagonal planar
Resonance Hybrid more stable than any of the resonance structure
Click here to view
Kekule
ResonanceDelocalization Energy
ΔH cyclohexene = -120kJmol-1
ΔH cyclohexa 13 diene = -240kJmol-1
ΔH cyclohexa 135 triene = -360kJmol-1
ΔH Benzene = -208kJmol-1
Enthalpy change hydrogenation
χ
helliphellip
bull Benzene lower in energy by 150kJbull More stable due to delocalization of π electrons
150kJ-150
3 Evidence for Benzene structure1
ResonanceDelocalization Energy
ΔH cyclohexene = -120kJmol-1
ΔH cyclohexa 13 diene = -240kJmol-1
ΔH cyclohexa 135 triene = -360kJmol-1
ΔH Benzene = -208kJmol-1
Enthalpy change hydrogenation
χ
helliphellip
bull Benzene lower in energy by 150kJbull More stable due to delocalization of π electrons
150kJ-150
C-CSingle bond
C=CDouble bond
C=CBenzene
Bond lengthpm 154 134 140
Bond enthalpykJmol-1
346 614 507
3 Evidence for Benzene structure1
2
bull X ray hit benzene crystalbull Interact with electron (electron density
map) bull X ray diffraction producedbull Bond length measured
X ray crystallography
NO singledouble bond detected
ResonanceDelocalization Energy
ΔH cyclohexene = -120kJmol-1
ΔH cyclohexa 13 diene = -240kJmol-1
ΔH cyclohexa 135 triene = -360kJmol-1
ΔH Benzene = -208kJmol-1
Enthalpy change hydrogenation
χ
helliphellip
bull Benzene lower in energy by 150kJbull More stable due to delocalization of π electrons
150kJ-150
C-CSingle bond
C=CDouble bond
C=CBenzene
Bond lengthpm 154 134 140
Bond enthalpykJmol-1
346 614 507
3 Evidence for Benzene structure1
2
Click here evidence against Kekule
bull X ray hit benzene crystalbull Interact with electron (electron density
map) bull X ray diffraction producedbull Bond length measured
X ray crystallography
NO singledouble bond detected
3 Addition reaction for unsaturated C=C
Addition reaction
Substitution reaction
NO double bond
Acknowledgements
Thanks to source of pictures and video used in this presentation
Thanks to Creative Commons for excellent contribution on licenseshttpspaceplacenasagovgreenhouseenhttpwwwozonedepletioninfoeducationpart3ozonesourceshtmlhttpcreativecommonsorglicenseshttpwwwciesinorgdocs011-462011-462htmlhttpwwwepmagazineorgstorage165benzene-evidenceaspx
Prepared by Lawrence Kok
Check out more video tutorials from my site and hope you enjoy this tutorialhttplawrencekokblogspotcom
FORMAL CHARGE (FC)
Formal ChargebullToolModel for comparing which Lewis structures is more acceptablebullTreats covalent bond with equal electron distribution no electronegativity differences bet atombullElectronegative atom has negative while least electronegative atom has positive formal charge
Formula formal charge
V - valence electrons of atom L ndash lone pair electronB ndash bonding electron molecule
Formal charge sulfur dioxide
formal charge for O
L +
formal charge for Oformal charge for O
L + L + L +
FORMAL CHARGE (FC)
Formal ChargebullToolModel for comparing which Lewis structures is more acceptablebullTreats covalent bond with equal electron distribution no electronegativity differences bet atombullElectronegative atom has negative while least electronegative atom has positive formal charge
Formula formal charge
V - valence electrons of atom L ndash lone pair electronB ndash bonding electron molecule
Formal charge sulfur dioxide
formal charge for O
V- Valence electron O = 6L- Lone pair electron O = 4B- Bonding electron O = 4
L +
FC = 6 ndash (4 +2) = 0
formal charge for O
V- Valence electron O = 6L- Lone pair electron O = 6B- Bonding electron O = 2
FC = 6 ndash (6+1) = -1
formal charge for O
V- Valence electron O = 6L - Lone pair electron O = 2B - Bonding electron O = 6
FC = 6 ndash (2+3) = +1
All resonance structure contribute to electronic structure Real structure is combination of themLowest formal charge (stable) contribute more than less stable structureSum of formal charges must be zero for neutral or equal to charge on ion
0+1
-1
L + L + L +
Ozone Good and Bad Good Side Bad Side
Ozone in Strastopherebull blocks UV B + C
Ozone in Troposphere act asbull Greenhouse gas
Ozone in ground level act as bullPollutant bullPhotochemical
Ozone Good and Bad Good Side Bad Side
Ozone in Strastopherebull blocks UV B + C
Ozone in Troposphere act asbull Greenhouse gas
Ozone in ground level act as bullPollutant bullPhotochemical
Click here on ozone depletion substances ODS (phaseout)
Why ozone able to absorb UV B and UV C
Breakdown of ozone ndash High UV radiation ndash Skin cancer - DNA mutation
Ozone depletion
UV Exposure
Ozone Hole
Ozone absorb UV radiation
Ozone absorb UV BC
O=O Double bond
O=O=OInter
mediate
Bond lengthpm 121 127
Bond enthalpykJ mol-1
498 364
Bond order 2 15
Dissociation by UV
lt242nm
lt330nm
Ozone weaker bondbullAbsorb UV AB(wavelength 330nm)
Bonding O2 and O3
Oxygen stronger bondbullAbsorb UV C (wavelength 230nm)
How ozone layer protect life on earth How Ozone
protect
Ozone absorb UV radiation
Ozone absorb UV BC
Ozone formation
O=O Double bond
O=O=OInter
mediate
Bond lengthpm 121 127
Bond enthalpykJ mol-1
498 364
Bond order 2 15
Dissociation by UV
lt242nm
lt330nm
Ozone weaker bondbullAbsorb UV AB(wavelength 330nm)
Bonding O2 and O3
Oxygen stronger bondbullAbsorb UV C (wavelength 230nm)
How ozone layer protect life on earth
Ozone Cycle
How Ozone
protect
Oxygen split by high UV to O (radical)
O radical combine to form ozone
1
2
3 Ozone (stratosphere) absorb UV BC
4Ozone reform again
Ozone createddestroyed by Chapman cycle
Oxygen reform again
Ozone absorb UV radiation
Ozone absorb UV BC
Ozone formation
O=O Double bond
O=O=OInter
mediate
Bond lengthpm 121 127
Bond enthalpykJ mol-1
498 364
Bond order 2 15
Dissociation by UV
lt242nm
lt330nm
Ozone weaker bondbullAbsorb UV AB(wavelength 330nm)
Bonding O2 and O3
Oxygen stronger bondbullAbsorb UV C (wavelength 230nm)
Free radical -reactive species with unpair electron
How ozone layer protect life on earth
Ozone Cycle
How Ozone
protect
Oxygen split by high UV to O (radical)
O radical combine to form ozone
1
2
3 Ozone (stratosphere) absorb UV BC
4Ozone reform again
Ozone cycle
Ozone createddestroyed by Chapman cycle
Oxygen reform again
Ozone absorb UV BC
CFC breaks down
How CFC breaks down
High UV BC
How CI radical destroy ozone
Catalytic destruction of ozone
Ozone Depleting Substances (ODS)
Carbon
Fluorine
Chlorine
Ozone absorb UV BC
CFC breaks down
How CFC breaks down
High UV BC
How CI radical destroy ozone
Catalytic destruction of ozone
Ozone Depleting Substances (ODS)
CI free radicals form
CImiddot react O3 form CIOmiddot radical
CIOmiddot react Omiddot form CImiddot radical again
Net eqn- ozone break down
Carbon
Fluorine
Chlorine
Ozone absorb UV BC
CFC breaks down
How CFC breaks down
High UV BC
How CI radical destroy ozone
Catalytic destruction of ozone
Ozone Depleting Substances (ODS)
How CFC destroys ozone
CI free radicals form
CImiddot react O3 form CIOmiddot radical
CIOmiddot react Omiddot form CImiddot radical again
Net eqn- ozone break down
Carbon
Fluorine
Chlorine
CI radical catalyzes again
Ozone absorb UV BC
How NO radical destroy ozone
Catalytic destruction of ozone
Ozone Depleting Substances (ODS)
Oxides of Nitrogen
Nitrogen Dioxide (NO2)
Nitrogen monoxide (nitric oxide NO)
Nitrous oxideN2O
Break down to form NO free radical (unpair electron)
+
Ozone absorb UV BC
NOx breaks down
How CFC breaks down
High UV BCHow NO radical destroy ozone
Catalytic destruction of ozone
Ozone Depleting Substances (ODS)
NO free radicals form
NO react O3 form NO2 radical
NO2 react O form NO radical again
Net eqn- ozone breaks down
Oxides of Nitrogen
Nitrogen Dioxide (NO2)
Nitrogen monoxide (nitric oxide NO)
Nitrous oxideN2O
Break down to form NO free radical (unpair electron)
NO NO2
NO2 NO + O2
+
Ozone absorb UV BC
NOx breaks down
How CFC breaks down
High UV BCHow NO radical destroy ozone
Catalytic destruction of ozone
Ozone Depleting Substances (ODS)
NO free radicals form
NO react O3 form NO2 radical
NO2 react O form NO radical again
Net eqn- ozone breaks down
Oxides of Nitrogen
Nitrogen Dioxide (NO2)
Nitrogen monoxide (nitric oxide NO)
Nitrous oxideN2O
Break down to form NO free radical (unpair electron)
NO NO2
NO2 NO + O2
Sources of NOx
Catalytic destruction of ozone
Ozone Depleting Substances (ODS)
Source of ODSbullHalogenated substancebullMan-made halocarbon refrigerant solvent propellantbullFoam-blowing agent (CFCs HCFCs freons halons)
Trichloroflouromethane CFC-11
Dichlorodifluoromethane CFC-12
Chlorodifluoromethane HCFC-22
Catalytic destruction of ozone
Ozone Depleting Substances (ODS)
Source of ODSbullHalogenated substancebullMan-made halocarbon refrigerant solvent propellantbullFoam-blowing agent (CFCs HCFCs freons halons)
CFCbullContain chlorine fluorine and carbon atomsbullExtremely stable with strong bonds long half lifebullStability allows CFC into the stratosphere bullHigh UV radiation reacts with CFCbullHigh UV photons breaks CFC (photochemical decomposition) bull Free Cl radicals form - destroying ozone
Trichloroflouromethane CFC-11
Dichlorodifluoromethane CFC-12
Chlorodifluoromethane HCFC-22
Why halogenate
d CFC used
Less harmful
Very harmful
Catalytic destruction of ozone
Ozone Depleting Substances (ODS)
Source of ODSbullHalogenated substancebullMan-made halocarbon refrigerant solvent propellantbullFoam-blowing agent (CFCs HCFCs freons halons)
Montreal Protocol bans CFC halon and ODS like carbon tetrachloride and trichloroethane
CFCbullContain chlorine fluorine and carbon atomsbullExtremely stable with strong bonds long half lifebullStability allows CFC into the stratosphere bullHigh UV radiation reacts with CFCbullHigh UV photons breaks CFC (photochemical decomposition) bull Free Cl radicals form - destroying ozone
Trichloroflouromethane CFC-11
Dichlorodifluoromethane CFC-12
Chlorodifluoromethane HCFC-22
Why halogenate
d CFC used
Less harmful
Very harmful
Why fluorinated is safer
Delocalization of electrons
Resonance bull Describing delocalization of electrons within a moleculepolyatomic ion where bonding cannot be express by ONE single Lewis structurebullDelocalization of π bond ndash π electrons spread over more than 2 nucleibullπ electrons are sharedbullπ electrons spread ndash more stable
Resonance structures benzene
Benzene6HC6
resonance structure 1 resonance structure 2
bull Unhybridised p orbitalbull Delocalization electrons above below planebull sp2 hybridization on carbon center
Delocalized electrons
Kekuleacute structure Cyclohexa- 135 triene
χ doublesingle bonds bet them
Benzene
Hexagonal planar
Kekule
Delocalization of electrons
Resonance bull Describing delocalization of electrons within a moleculepolyatomic ion where bonding cannot be express by ONE single Lewis structurebullDelocalization of π bond ndash π electrons spread over more than 2 nucleibullπ electrons are sharedbullπ electrons spread ndash more stable
Resonance structures benzene
Benzene6HC6
resonance structure 1 resonance structure 2
Resonance hybrid
bull All bonds C6H6 are identical in length strengthbull Hybrid of 2 resonance structuresbull No C-C (single) or C=C (double) bonds foundbull Only C ----- C bondbull Intermediate character bet singledouble bond
bull Bond Order =
bull Unhybridised p orbitalbull Delocalization electrons above below planebull sp2 hybridization on carbon center
15
Click here to view
Delocalized electrons
Kekuleacute structure Cyclohexa- 135 triene
χ doublesingle bonds bet them
Benzene
Hexagonal planar
Resonance Hybrid more stable than any of the resonance structure
Click here to view
Kekule
ResonanceDelocalization Energy
ΔH cyclohexene = -120kJmol-1
ΔH cyclohexa 13 diene = -240kJmol-1
ΔH cyclohexa 135 triene = -360kJmol-1
ΔH Benzene = -208kJmol-1
Enthalpy change hydrogenation
χ
helliphellip
bull Benzene lower in energy by 150kJbull More stable due to delocalization of π electrons
150kJ-150
3 Evidence for Benzene structure1
ResonanceDelocalization Energy
ΔH cyclohexene = -120kJmol-1
ΔH cyclohexa 13 diene = -240kJmol-1
ΔH cyclohexa 135 triene = -360kJmol-1
ΔH Benzene = -208kJmol-1
Enthalpy change hydrogenation
χ
helliphellip
bull Benzene lower in energy by 150kJbull More stable due to delocalization of π electrons
150kJ-150
C-CSingle bond
C=CDouble bond
C=CBenzene
Bond lengthpm 154 134 140
Bond enthalpykJmol-1
346 614 507
3 Evidence for Benzene structure1
2
bull X ray hit benzene crystalbull Interact with electron (electron density
map) bull X ray diffraction producedbull Bond length measured
X ray crystallography
NO singledouble bond detected
ResonanceDelocalization Energy
ΔH cyclohexene = -120kJmol-1
ΔH cyclohexa 13 diene = -240kJmol-1
ΔH cyclohexa 135 triene = -360kJmol-1
ΔH Benzene = -208kJmol-1
Enthalpy change hydrogenation
χ
helliphellip
bull Benzene lower in energy by 150kJbull More stable due to delocalization of π electrons
150kJ-150
C-CSingle bond
C=CDouble bond
C=CBenzene
Bond lengthpm 154 134 140
Bond enthalpykJmol-1
346 614 507
3 Evidence for Benzene structure1
2
Click here evidence against Kekule
bull X ray hit benzene crystalbull Interact with electron (electron density
map) bull X ray diffraction producedbull Bond length measured
X ray crystallography
NO singledouble bond detected
3 Addition reaction for unsaturated C=C
Addition reaction
Substitution reaction
NO double bond
Acknowledgements
Thanks to source of pictures and video used in this presentation
Thanks to Creative Commons for excellent contribution on licenseshttpspaceplacenasagovgreenhouseenhttpwwwozonedepletioninfoeducationpart3ozonesourceshtmlhttpcreativecommonsorglicenseshttpwwwciesinorgdocs011-462011-462htmlhttpwwwepmagazineorgstorage165benzene-evidenceaspx
Prepared by Lawrence Kok
Check out more video tutorials from my site and hope you enjoy this tutorialhttplawrencekokblogspotcom
FORMAL CHARGE (FC)
Formal ChargebullToolModel for comparing which Lewis structures is more acceptablebullTreats covalent bond with equal electron distribution no electronegativity differences bet atombullElectronegative atom has negative while least electronegative atom has positive formal charge
Formula formal charge
V - valence electrons of atom L ndash lone pair electronB ndash bonding electron molecule
Formal charge sulfur dioxide
formal charge for O
V- Valence electron O = 6L- Lone pair electron O = 4B- Bonding electron O = 4
L +
FC = 6 ndash (4 +2) = 0
formal charge for O
V- Valence electron O = 6L- Lone pair electron O = 6B- Bonding electron O = 2
FC = 6 ndash (6+1) = -1
formal charge for O
V- Valence electron O = 6L - Lone pair electron O = 2B - Bonding electron O = 6
FC = 6 ndash (2+3) = +1
All resonance structure contribute to electronic structure Real structure is combination of themLowest formal charge (stable) contribute more than less stable structureSum of formal charges must be zero for neutral or equal to charge on ion
0+1
-1
L + L + L +
Ozone Good and Bad Good Side Bad Side
Ozone in Strastopherebull blocks UV B + C
Ozone in Troposphere act asbull Greenhouse gas
Ozone in ground level act as bullPollutant bullPhotochemical
Ozone Good and Bad Good Side Bad Side
Ozone in Strastopherebull blocks UV B + C
Ozone in Troposphere act asbull Greenhouse gas
Ozone in ground level act as bullPollutant bullPhotochemical
Click here on ozone depletion substances ODS (phaseout)
Why ozone able to absorb UV B and UV C
Breakdown of ozone ndash High UV radiation ndash Skin cancer - DNA mutation
Ozone depletion
UV Exposure
Ozone Hole
Ozone absorb UV radiation
Ozone absorb UV BC
O=O Double bond
O=O=OInter
mediate
Bond lengthpm 121 127
Bond enthalpykJ mol-1
498 364
Bond order 2 15
Dissociation by UV
lt242nm
lt330nm
Ozone weaker bondbullAbsorb UV AB(wavelength 330nm)
Bonding O2 and O3
Oxygen stronger bondbullAbsorb UV C (wavelength 230nm)
How ozone layer protect life on earth How Ozone
protect
Ozone absorb UV radiation
Ozone absorb UV BC
Ozone formation
O=O Double bond
O=O=OInter
mediate
Bond lengthpm 121 127
Bond enthalpykJ mol-1
498 364
Bond order 2 15
Dissociation by UV
lt242nm
lt330nm
Ozone weaker bondbullAbsorb UV AB(wavelength 330nm)
Bonding O2 and O3
Oxygen stronger bondbullAbsorb UV C (wavelength 230nm)
How ozone layer protect life on earth
Ozone Cycle
How Ozone
protect
Oxygen split by high UV to O (radical)
O radical combine to form ozone
1
2
3 Ozone (stratosphere) absorb UV BC
4Ozone reform again
Ozone createddestroyed by Chapman cycle
Oxygen reform again
Ozone absorb UV radiation
Ozone absorb UV BC
Ozone formation
O=O Double bond
O=O=OInter
mediate
Bond lengthpm 121 127
Bond enthalpykJ mol-1
498 364
Bond order 2 15
Dissociation by UV
lt242nm
lt330nm
Ozone weaker bondbullAbsorb UV AB(wavelength 330nm)
Bonding O2 and O3
Oxygen stronger bondbullAbsorb UV C (wavelength 230nm)
Free radical -reactive species with unpair electron
How ozone layer protect life on earth
Ozone Cycle
How Ozone
protect
Oxygen split by high UV to O (radical)
O radical combine to form ozone
1
2
3 Ozone (stratosphere) absorb UV BC
4Ozone reform again
Ozone cycle
Ozone createddestroyed by Chapman cycle
Oxygen reform again
Ozone absorb UV BC
CFC breaks down
How CFC breaks down
High UV BC
How CI radical destroy ozone
Catalytic destruction of ozone
Ozone Depleting Substances (ODS)
Carbon
Fluorine
Chlorine
Ozone absorb UV BC
CFC breaks down
How CFC breaks down
High UV BC
How CI radical destroy ozone
Catalytic destruction of ozone
Ozone Depleting Substances (ODS)
CI free radicals form
CImiddot react O3 form CIOmiddot radical
CIOmiddot react Omiddot form CImiddot radical again
Net eqn- ozone break down
Carbon
Fluorine
Chlorine
Ozone absorb UV BC
CFC breaks down
How CFC breaks down
High UV BC
How CI radical destroy ozone
Catalytic destruction of ozone
Ozone Depleting Substances (ODS)
How CFC destroys ozone
CI free radicals form
CImiddot react O3 form CIOmiddot radical
CIOmiddot react Omiddot form CImiddot radical again
Net eqn- ozone break down
Carbon
Fluorine
Chlorine
CI radical catalyzes again
Ozone absorb UV BC
How NO radical destroy ozone
Catalytic destruction of ozone
Ozone Depleting Substances (ODS)
Oxides of Nitrogen
Nitrogen Dioxide (NO2)
Nitrogen monoxide (nitric oxide NO)
Nitrous oxideN2O
Break down to form NO free radical (unpair electron)
+
Ozone absorb UV BC
NOx breaks down
How CFC breaks down
High UV BCHow NO radical destroy ozone
Catalytic destruction of ozone
Ozone Depleting Substances (ODS)
NO free radicals form
NO react O3 form NO2 radical
NO2 react O form NO radical again
Net eqn- ozone breaks down
Oxides of Nitrogen
Nitrogen Dioxide (NO2)
Nitrogen monoxide (nitric oxide NO)
Nitrous oxideN2O
Break down to form NO free radical (unpair electron)
NO NO2
NO2 NO + O2
+
Ozone absorb UV BC
NOx breaks down
How CFC breaks down
High UV BCHow NO radical destroy ozone
Catalytic destruction of ozone
Ozone Depleting Substances (ODS)
NO free radicals form
NO react O3 form NO2 radical
NO2 react O form NO radical again
Net eqn- ozone breaks down
Oxides of Nitrogen
Nitrogen Dioxide (NO2)
Nitrogen monoxide (nitric oxide NO)
Nitrous oxideN2O
Break down to form NO free radical (unpair electron)
NO NO2
NO2 NO + O2
Sources of NOx
Catalytic destruction of ozone
Ozone Depleting Substances (ODS)
Source of ODSbullHalogenated substancebullMan-made halocarbon refrigerant solvent propellantbullFoam-blowing agent (CFCs HCFCs freons halons)
Trichloroflouromethane CFC-11
Dichlorodifluoromethane CFC-12
Chlorodifluoromethane HCFC-22
Catalytic destruction of ozone
Ozone Depleting Substances (ODS)
Source of ODSbullHalogenated substancebullMan-made halocarbon refrigerant solvent propellantbullFoam-blowing agent (CFCs HCFCs freons halons)
CFCbullContain chlorine fluorine and carbon atomsbullExtremely stable with strong bonds long half lifebullStability allows CFC into the stratosphere bullHigh UV radiation reacts with CFCbullHigh UV photons breaks CFC (photochemical decomposition) bull Free Cl radicals form - destroying ozone
Trichloroflouromethane CFC-11
Dichlorodifluoromethane CFC-12
Chlorodifluoromethane HCFC-22
Why halogenate
d CFC used
Less harmful
Very harmful
Catalytic destruction of ozone
Ozone Depleting Substances (ODS)
Source of ODSbullHalogenated substancebullMan-made halocarbon refrigerant solvent propellantbullFoam-blowing agent (CFCs HCFCs freons halons)
Montreal Protocol bans CFC halon and ODS like carbon tetrachloride and trichloroethane
CFCbullContain chlorine fluorine and carbon atomsbullExtremely stable with strong bonds long half lifebullStability allows CFC into the stratosphere bullHigh UV radiation reacts with CFCbullHigh UV photons breaks CFC (photochemical decomposition) bull Free Cl radicals form - destroying ozone
Trichloroflouromethane CFC-11
Dichlorodifluoromethane CFC-12
Chlorodifluoromethane HCFC-22
Why halogenate
d CFC used
Less harmful
Very harmful
Why fluorinated is safer
Delocalization of electrons
Resonance bull Describing delocalization of electrons within a moleculepolyatomic ion where bonding cannot be express by ONE single Lewis structurebullDelocalization of π bond ndash π electrons spread over more than 2 nucleibullπ electrons are sharedbullπ electrons spread ndash more stable
Resonance structures benzene
Benzene6HC6
resonance structure 1 resonance structure 2
bull Unhybridised p orbitalbull Delocalization electrons above below planebull sp2 hybridization on carbon center
Delocalized electrons
Kekuleacute structure Cyclohexa- 135 triene
χ doublesingle bonds bet them
Benzene
Hexagonal planar
Kekule
Delocalization of electrons
Resonance bull Describing delocalization of electrons within a moleculepolyatomic ion where bonding cannot be express by ONE single Lewis structurebullDelocalization of π bond ndash π electrons spread over more than 2 nucleibullπ electrons are sharedbullπ electrons spread ndash more stable
Resonance structures benzene
Benzene6HC6
resonance structure 1 resonance structure 2
Resonance hybrid
bull All bonds C6H6 are identical in length strengthbull Hybrid of 2 resonance structuresbull No C-C (single) or C=C (double) bonds foundbull Only C ----- C bondbull Intermediate character bet singledouble bond
bull Bond Order =
bull Unhybridised p orbitalbull Delocalization electrons above below planebull sp2 hybridization on carbon center
15
Click here to view
Delocalized electrons
Kekuleacute structure Cyclohexa- 135 triene
χ doublesingle bonds bet them
Benzene
Hexagonal planar
Resonance Hybrid more stable than any of the resonance structure
Click here to view
Kekule
ResonanceDelocalization Energy
ΔH cyclohexene = -120kJmol-1
ΔH cyclohexa 13 diene = -240kJmol-1
ΔH cyclohexa 135 triene = -360kJmol-1
ΔH Benzene = -208kJmol-1
Enthalpy change hydrogenation
χ
helliphellip
bull Benzene lower in energy by 150kJbull More stable due to delocalization of π electrons
150kJ-150
3 Evidence for Benzene structure1
ResonanceDelocalization Energy
ΔH cyclohexene = -120kJmol-1
ΔH cyclohexa 13 diene = -240kJmol-1
ΔH cyclohexa 135 triene = -360kJmol-1
ΔH Benzene = -208kJmol-1
Enthalpy change hydrogenation
χ
helliphellip
bull Benzene lower in energy by 150kJbull More stable due to delocalization of π electrons
150kJ-150
C-CSingle bond
C=CDouble bond
C=CBenzene
Bond lengthpm 154 134 140
Bond enthalpykJmol-1
346 614 507
3 Evidence for Benzene structure1
2
bull X ray hit benzene crystalbull Interact with electron (electron density
map) bull X ray diffraction producedbull Bond length measured
X ray crystallography
NO singledouble bond detected
ResonanceDelocalization Energy
ΔH cyclohexene = -120kJmol-1
ΔH cyclohexa 13 diene = -240kJmol-1
ΔH cyclohexa 135 triene = -360kJmol-1
ΔH Benzene = -208kJmol-1
Enthalpy change hydrogenation
χ
helliphellip
bull Benzene lower in energy by 150kJbull More stable due to delocalization of π electrons
150kJ-150
C-CSingle bond
C=CDouble bond
C=CBenzene
Bond lengthpm 154 134 140
Bond enthalpykJmol-1
346 614 507
3 Evidence for Benzene structure1
2
Click here evidence against Kekule
bull X ray hit benzene crystalbull Interact with electron (electron density
map) bull X ray diffraction producedbull Bond length measured
X ray crystallography
NO singledouble bond detected
3 Addition reaction for unsaturated C=C
Addition reaction
Substitution reaction
NO double bond
Acknowledgements
Thanks to source of pictures and video used in this presentation
Thanks to Creative Commons for excellent contribution on licenseshttpspaceplacenasagovgreenhouseenhttpwwwozonedepletioninfoeducationpart3ozonesourceshtmlhttpcreativecommonsorglicenseshttpwwwciesinorgdocs011-462011-462htmlhttpwwwepmagazineorgstorage165benzene-evidenceaspx
Prepared by Lawrence Kok
Check out more video tutorials from my site and hope you enjoy this tutorialhttplawrencekokblogspotcom
Ozone Good and Bad Good Side Bad Side
Ozone in Strastopherebull blocks UV B + C
Ozone in Troposphere act asbull Greenhouse gas
Ozone in ground level act as bullPollutant bullPhotochemical
Ozone Good and Bad Good Side Bad Side
Ozone in Strastopherebull blocks UV B + C
Ozone in Troposphere act asbull Greenhouse gas
Ozone in ground level act as bullPollutant bullPhotochemical
Click here on ozone depletion substances ODS (phaseout)
Why ozone able to absorb UV B and UV C
Breakdown of ozone ndash High UV radiation ndash Skin cancer - DNA mutation
Ozone depletion
UV Exposure
Ozone Hole
Ozone absorb UV radiation
Ozone absorb UV BC
O=O Double bond
O=O=OInter
mediate
Bond lengthpm 121 127
Bond enthalpykJ mol-1
498 364
Bond order 2 15
Dissociation by UV
lt242nm
lt330nm
Ozone weaker bondbullAbsorb UV AB(wavelength 330nm)
Bonding O2 and O3
Oxygen stronger bondbullAbsorb UV C (wavelength 230nm)
How ozone layer protect life on earth How Ozone
protect
Ozone absorb UV radiation
Ozone absorb UV BC
Ozone formation
O=O Double bond
O=O=OInter
mediate
Bond lengthpm 121 127
Bond enthalpykJ mol-1
498 364
Bond order 2 15
Dissociation by UV
lt242nm
lt330nm
Ozone weaker bondbullAbsorb UV AB(wavelength 330nm)
Bonding O2 and O3
Oxygen stronger bondbullAbsorb UV C (wavelength 230nm)
How ozone layer protect life on earth
Ozone Cycle
How Ozone
protect
Oxygen split by high UV to O (radical)
O radical combine to form ozone
1
2
3 Ozone (stratosphere) absorb UV BC
4Ozone reform again
Ozone createddestroyed by Chapman cycle
Oxygen reform again
Ozone absorb UV radiation
Ozone absorb UV BC
Ozone formation
O=O Double bond
O=O=OInter
mediate
Bond lengthpm 121 127
Bond enthalpykJ mol-1
498 364
Bond order 2 15
Dissociation by UV
lt242nm
lt330nm
Ozone weaker bondbullAbsorb UV AB(wavelength 330nm)
Bonding O2 and O3
Oxygen stronger bondbullAbsorb UV C (wavelength 230nm)
Free radical -reactive species with unpair electron
How ozone layer protect life on earth
Ozone Cycle
How Ozone
protect
Oxygen split by high UV to O (radical)
O radical combine to form ozone
1
2
3 Ozone (stratosphere) absorb UV BC
4Ozone reform again
Ozone cycle
Ozone createddestroyed by Chapman cycle
Oxygen reform again
Ozone absorb UV BC
CFC breaks down
How CFC breaks down
High UV BC
How CI radical destroy ozone
Catalytic destruction of ozone
Ozone Depleting Substances (ODS)
Carbon
Fluorine
Chlorine
Ozone absorb UV BC
CFC breaks down
How CFC breaks down
High UV BC
How CI radical destroy ozone
Catalytic destruction of ozone
Ozone Depleting Substances (ODS)
CI free radicals form
CImiddot react O3 form CIOmiddot radical
CIOmiddot react Omiddot form CImiddot radical again
Net eqn- ozone break down
Carbon
Fluorine
Chlorine
Ozone absorb UV BC
CFC breaks down
How CFC breaks down
High UV BC
How CI radical destroy ozone
Catalytic destruction of ozone
Ozone Depleting Substances (ODS)
How CFC destroys ozone
CI free radicals form
CImiddot react O3 form CIOmiddot radical
CIOmiddot react Omiddot form CImiddot radical again
Net eqn- ozone break down
Carbon
Fluorine
Chlorine
CI radical catalyzes again
Ozone absorb UV BC
How NO radical destroy ozone
Catalytic destruction of ozone
Ozone Depleting Substances (ODS)
Oxides of Nitrogen
Nitrogen Dioxide (NO2)
Nitrogen monoxide (nitric oxide NO)
Nitrous oxideN2O
Break down to form NO free radical (unpair electron)
+
Ozone absorb UV BC
NOx breaks down
How CFC breaks down
High UV BCHow NO radical destroy ozone
Catalytic destruction of ozone
Ozone Depleting Substances (ODS)
NO free radicals form
NO react O3 form NO2 radical
NO2 react O form NO radical again
Net eqn- ozone breaks down
Oxides of Nitrogen
Nitrogen Dioxide (NO2)
Nitrogen monoxide (nitric oxide NO)
Nitrous oxideN2O
Break down to form NO free radical (unpair electron)
NO NO2
NO2 NO + O2
+
Ozone absorb UV BC
NOx breaks down
How CFC breaks down
High UV BCHow NO radical destroy ozone
Catalytic destruction of ozone
Ozone Depleting Substances (ODS)
NO free radicals form
NO react O3 form NO2 radical
NO2 react O form NO radical again
Net eqn- ozone breaks down
Oxides of Nitrogen
Nitrogen Dioxide (NO2)
Nitrogen monoxide (nitric oxide NO)
Nitrous oxideN2O
Break down to form NO free radical (unpair electron)
NO NO2
NO2 NO + O2
Sources of NOx
Catalytic destruction of ozone
Ozone Depleting Substances (ODS)
Source of ODSbullHalogenated substancebullMan-made halocarbon refrigerant solvent propellantbullFoam-blowing agent (CFCs HCFCs freons halons)
Trichloroflouromethane CFC-11
Dichlorodifluoromethane CFC-12
Chlorodifluoromethane HCFC-22
Catalytic destruction of ozone
Ozone Depleting Substances (ODS)
Source of ODSbullHalogenated substancebullMan-made halocarbon refrigerant solvent propellantbullFoam-blowing agent (CFCs HCFCs freons halons)
CFCbullContain chlorine fluorine and carbon atomsbullExtremely stable with strong bonds long half lifebullStability allows CFC into the stratosphere bullHigh UV radiation reacts with CFCbullHigh UV photons breaks CFC (photochemical decomposition) bull Free Cl radicals form - destroying ozone
Trichloroflouromethane CFC-11
Dichlorodifluoromethane CFC-12
Chlorodifluoromethane HCFC-22
Why halogenate
d CFC used
Less harmful
Very harmful
Catalytic destruction of ozone
Ozone Depleting Substances (ODS)
Source of ODSbullHalogenated substancebullMan-made halocarbon refrigerant solvent propellantbullFoam-blowing agent (CFCs HCFCs freons halons)
Montreal Protocol bans CFC halon and ODS like carbon tetrachloride and trichloroethane
CFCbullContain chlorine fluorine and carbon atomsbullExtremely stable with strong bonds long half lifebullStability allows CFC into the stratosphere bullHigh UV radiation reacts with CFCbullHigh UV photons breaks CFC (photochemical decomposition) bull Free Cl radicals form - destroying ozone
Trichloroflouromethane CFC-11
Dichlorodifluoromethane CFC-12
Chlorodifluoromethane HCFC-22
Why halogenate
d CFC used
Less harmful
Very harmful
Why fluorinated is safer
Delocalization of electrons
Resonance bull Describing delocalization of electrons within a moleculepolyatomic ion where bonding cannot be express by ONE single Lewis structurebullDelocalization of π bond ndash π electrons spread over more than 2 nucleibullπ electrons are sharedbullπ electrons spread ndash more stable
Resonance structures benzene
Benzene6HC6
resonance structure 1 resonance structure 2
bull Unhybridised p orbitalbull Delocalization electrons above below planebull sp2 hybridization on carbon center
Delocalized electrons
Kekuleacute structure Cyclohexa- 135 triene
χ doublesingle bonds bet them
Benzene
Hexagonal planar
Kekule
Delocalization of electrons
Resonance bull Describing delocalization of electrons within a moleculepolyatomic ion where bonding cannot be express by ONE single Lewis structurebullDelocalization of π bond ndash π electrons spread over more than 2 nucleibullπ electrons are sharedbullπ electrons spread ndash more stable
Resonance structures benzene
Benzene6HC6
resonance structure 1 resonance structure 2
Resonance hybrid
bull All bonds C6H6 are identical in length strengthbull Hybrid of 2 resonance structuresbull No C-C (single) or C=C (double) bonds foundbull Only C ----- C bondbull Intermediate character bet singledouble bond
bull Bond Order =
bull Unhybridised p orbitalbull Delocalization electrons above below planebull sp2 hybridization on carbon center
15
Click here to view
Delocalized electrons
Kekuleacute structure Cyclohexa- 135 triene
χ doublesingle bonds bet them
Benzene
Hexagonal planar
Resonance Hybrid more stable than any of the resonance structure
Click here to view
Kekule
ResonanceDelocalization Energy
ΔH cyclohexene = -120kJmol-1
ΔH cyclohexa 13 diene = -240kJmol-1
ΔH cyclohexa 135 triene = -360kJmol-1
ΔH Benzene = -208kJmol-1
Enthalpy change hydrogenation
χ
helliphellip
bull Benzene lower in energy by 150kJbull More stable due to delocalization of π electrons
150kJ-150
3 Evidence for Benzene structure1
ResonanceDelocalization Energy
ΔH cyclohexene = -120kJmol-1
ΔH cyclohexa 13 diene = -240kJmol-1
ΔH cyclohexa 135 triene = -360kJmol-1
ΔH Benzene = -208kJmol-1
Enthalpy change hydrogenation
χ
helliphellip
bull Benzene lower in energy by 150kJbull More stable due to delocalization of π electrons
150kJ-150
C-CSingle bond
C=CDouble bond
C=CBenzene
Bond lengthpm 154 134 140
Bond enthalpykJmol-1
346 614 507
3 Evidence for Benzene structure1
2
bull X ray hit benzene crystalbull Interact with electron (electron density
map) bull X ray diffraction producedbull Bond length measured
X ray crystallography
NO singledouble bond detected
ResonanceDelocalization Energy
ΔH cyclohexene = -120kJmol-1
ΔH cyclohexa 13 diene = -240kJmol-1
ΔH cyclohexa 135 triene = -360kJmol-1
ΔH Benzene = -208kJmol-1
Enthalpy change hydrogenation
χ
helliphellip
bull Benzene lower in energy by 150kJbull More stable due to delocalization of π electrons
150kJ-150
C-CSingle bond
C=CDouble bond
C=CBenzene
Bond lengthpm 154 134 140
Bond enthalpykJmol-1
346 614 507
3 Evidence for Benzene structure1
2
Click here evidence against Kekule
bull X ray hit benzene crystalbull Interact with electron (electron density
map) bull X ray diffraction producedbull Bond length measured
X ray crystallography
NO singledouble bond detected
3 Addition reaction for unsaturated C=C
Addition reaction
Substitution reaction
NO double bond
Acknowledgements
Thanks to source of pictures and video used in this presentation
Thanks to Creative Commons for excellent contribution on licenseshttpspaceplacenasagovgreenhouseenhttpwwwozonedepletioninfoeducationpart3ozonesourceshtmlhttpcreativecommonsorglicenseshttpwwwciesinorgdocs011-462011-462htmlhttpwwwepmagazineorgstorage165benzene-evidenceaspx
Prepared by Lawrence Kok
Check out more video tutorials from my site and hope you enjoy this tutorialhttplawrencekokblogspotcom
Ozone Good and Bad Good Side Bad Side
Ozone in Strastopherebull blocks UV B + C
Ozone in Troposphere act asbull Greenhouse gas
Ozone in ground level act as bullPollutant bullPhotochemical
Click here on ozone depletion substances ODS (phaseout)
Why ozone able to absorb UV B and UV C
Breakdown of ozone ndash High UV radiation ndash Skin cancer - DNA mutation
Ozone depletion
UV Exposure
Ozone Hole
Ozone absorb UV radiation
Ozone absorb UV BC
O=O Double bond
O=O=OInter
mediate
Bond lengthpm 121 127
Bond enthalpykJ mol-1
498 364
Bond order 2 15
Dissociation by UV
lt242nm
lt330nm
Ozone weaker bondbullAbsorb UV AB(wavelength 330nm)
Bonding O2 and O3
Oxygen stronger bondbullAbsorb UV C (wavelength 230nm)
How ozone layer protect life on earth How Ozone
protect
Ozone absorb UV radiation
Ozone absorb UV BC
Ozone formation
O=O Double bond
O=O=OInter
mediate
Bond lengthpm 121 127
Bond enthalpykJ mol-1
498 364
Bond order 2 15
Dissociation by UV
lt242nm
lt330nm
Ozone weaker bondbullAbsorb UV AB(wavelength 330nm)
Bonding O2 and O3
Oxygen stronger bondbullAbsorb UV C (wavelength 230nm)
How ozone layer protect life on earth
Ozone Cycle
How Ozone
protect
Oxygen split by high UV to O (radical)
O radical combine to form ozone
1
2
3 Ozone (stratosphere) absorb UV BC
4Ozone reform again
Ozone createddestroyed by Chapman cycle
Oxygen reform again
Ozone absorb UV radiation
Ozone absorb UV BC
Ozone formation
O=O Double bond
O=O=OInter
mediate
Bond lengthpm 121 127
Bond enthalpykJ mol-1
498 364
Bond order 2 15
Dissociation by UV
lt242nm
lt330nm
Ozone weaker bondbullAbsorb UV AB(wavelength 330nm)
Bonding O2 and O3
Oxygen stronger bondbullAbsorb UV C (wavelength 230nm)
Free radical -reactive species with unpair electron
How ozone layer protect life on earth
Ozone Cycle
How Ozone
protect
Oxygen split by high UV to O (radical)
O radical combine to form ozone
1
2
3 Ozone (stratosphere) absorb UV BC
4Ozone reform again
Ozone cycle
Ozone createddestroyed by Chapman cycle
Oxygen reform again
Ozone absorb UV BC
CFC breaks down
How CFC breaks down
High UV BC
How CI radical destroy ozone
Catalytic destruction of ozone
Ozone Depleting Substances (ODS)
Carbon
Fluorine
Chlorine
Ozone absorb UV BC
CFC breaks down
How CFC breaks down
High UV BC
How CI radical destroy ozone
Catalytic destruction of ozone
Ozone Depleting Substances (ODS)
CI free radicals form
CImiddot react O3 form CIOmiddot radical
CIOmiddot react Omiddot form CImiddot radical again
Net eqn- ozone break down
Carbon
Fluorine
Chlorine
Ozone absorb UV BC
CFC breaks down
How CFC breaks down
High UV BC
How CI radical destroy ozone
Catalytic destruction of ozone
Ozone Depleting Substances (ODS)
How CFC destroys ozone
CI free radicals form
CImiddot react O3 form CIOmiddot radical
CIOmiddot react Omiddot form CImiddot radical again
Net eqn- ozone break down
Carbon
Fluorine
Chlorine
CI radical catalyzes again
Ozone absorb UV BC
How NO radical destroy ozone
Catalytic destruction of ozone
Ozone Depleting Substances (ODS)
Oxides of Nitrogen
Nitrogen Dioxide (NO2)
Nitrogen monoxide (nitric oxide NO)
Nitrous oxideN2O
Break down to form NO free radical (unpair electron)
+
Ozone absorb UV BC
NOx breaks down
How CFC breaks down
High UV BCHow NO radical destroy ozone
Catalytic destruction of ozone
Ozone Depleting Substances (ODS)
NO free radicals form
NO react O3 form NO2 radical
NO2 react O form NO radical again
Net eqn- ozone breaks down
Oxides of Nitrogen
Nitrogen Dioxide (NO2)
Nitrogen monoxide (nitric oxide NO)
Nitrous oxideN2O
Break down to form NO free radical (unpair electron)
NO NO2
NO2 NO + O2
+
Ozone absorb UV BC
NOx breaks down
How CFC breaks down
High UV BCHow NO radical destroy ozone
Catalytic destruction of ozone
Ozone Depleting Substances (ODS)
NO free radicals form
NO react O3 form NO2 radical
NO2 react O form NO radical again
Net eqn- ozone breaks down
Oxides of Nitrogen
Nitrogen Dioxide (NO2)
Nitrogen monoxide (nitric oxide NO)
Nitrous oxideN2O
Break down to form NO free radical (unpair electron)
NO NO2
NO2 NO + O2
Sources of NOx
Catalytic destruction of ozone
Ozone Depleting Substances (ODS)
Source of ODSbullHalogenated substancebullMan-made halocarbon refrigerant solvent propellantbullFoam-blowing agent (CFCs HCFCs freons halons)
Trichloroflouromethane CFC-11
Dichlorodifluoromethane CFC-12
Chlorodifluoromethane HCFC-22
Catalytic destruction of ozone
Ozone Depleting Substances (ODS)
Source of ODSbullHalogenated substancebullMan-made halocarbon refrigerant solvent propellantbullFoam-blowing agent (CFCs HCFCs freons halons)
CFCbullContain chlorine fluorine and carbon atomsbullExtremely stable with strong bonds long half lifebullStability allows CFC into the stratosphere bullHigh UV radiation reacts with CFCbullHigh UV photons breaks CFC (photochemical decomposition) bull Free Cl radicals form - destroying ozone
Trichloroflouromethane CFC-11
Dichlorodifluoromethane CFC-12
Chlorodifluoromethane HCFC-22
Why halogenate
d CFC used
Less harmful
Very harmful
Catalytic destruction of ozone
Ozone Depleting Substances (ODS)
Source of ODSbullHalogenated substancebullMan-made halocarbon refrigerant solvent propellantbullFoam-blowing agent (CFCs HCFCs freons halons)
Montreal Protocol bans CFC halon and ODS like carbon tetrachloride and trichloroethane
CFCbullContain chlorine fluorine and carbon atomsbullExtremely stable with strong bonds long half lifebullStability allows CFC into the stratosphere bullHigh UV radiation reacts with CFCbullHigh UV photons breaks CFC (photochemical decomposition) bull Free Cl radicals form - destroying ozone
Trichloroflouromethane CFC-11
Dichlorodifluoromethane CFC-12
Chlorodifluoromethane HCFC-22
Why halogenate
d CFC used
Less harmful
Very harmful
Why fluorinated is safer
Delocalization of electrons
Resonance bull Describing delocalization of electrons within a moleculepolyatomic ion where bonding cannot be express by ONE single Lewis structurebullDelocalization of π bond ndash π electrons spread over more than 2 nucleibullπ electrons are sharedbullπ electrons spread ndash more stable
Resonance structures benzene
Benzene6HC6
resonance structure 1 resonance structure 2
bull Unhybridised p orbitalbull Delocalization electrons above below planebull sp2 hybridization on carbon center
Delocalized electrons
Kekuleacute structure Cyclohexa- 135 triene
χ doublesingle bonds bet them
Benzene
Hexagonal planar
Kekule
Delocalization of electrons
Resonance bull Describing delocalization of electrons within a moleculepolyatomic ion where bonding cannot be express by ONE single Lewis structurebullDelocalization of π bond ndash π electrons spread over more than 2 nucleibullπ electrons are sharedbullπ electrons spread ndash more stable
Resonance structures benzene
Benzene6HC6
resonance structure 1 resonance structure 2
Resonance hybrid
bull All bonds C6H6 are identical in length strengthbull Hybrid of 2 resonance structuresbull No C-C (single) or C=C (double) bonds foundbull Only C ----- C bondbull Intermediate character bet singledouble bond
bull Bond Order =
bull Unhybridised p orbitalbull Delocalization electrons above below planebull sp2 hybridization on carbon center
15
Click here to view
Delocalized electrons
Kekuleacute structure Cyclohexa- 135 triene
χ doublesingle bonds bet them
Benzene
Hexagonal planar
Resonance Hybrid more stable than any of the resonance structure
Click here to view
Kekule
ResonanceDelocalization Energy
ΔH cyclohexene = -120kJmol-1
ΔH cyclohexa 13 diene = -240kJmol-1
ΔH cyclohexa 135 triene = -360kJmol-1
ΔH Benzene = -208kJmol-1
Enthalpy change hydrogenation
χ
helliphellip
bull Benzene lower in energy by 150kJbull More stable due to delocalization of π electrons
150kJ-150
3 Evidence for Benzene structure1
ResonanceDelocalization Energy
ΔH cyclohexene = -120kJmol-1
ΔH cyclohexa 13 diene = -240kJmol-1
ΔH cyclohexa 135 triene = -360kJmol-1
ΔH Benzene = -208kJmol-1
Enthalpy change hydrogenation
χ
helliphellip
bull Benzene lower in energy by 150kJbull More stable due to delocalization of π electrons
150kJ-150
C-CSingle bond
C=CDouble bond
C=CBenzene
Bond lengthpm 154 134 140
Bond enthalpykJmol-1
346 614 507
3 Evidence for Benzene structure1
2
bull X ray hit benzene crystalbull Interact with electron (electron density
map) bull X ray diffraction producedbull Bond length measured
X ray crystallography
NO singledouble bond detected
ResonanceDelocalization Energy
ΔH cyclohexene = -120kJmol-1
ΔH cyclohexa 13 diene = -240kJmol-1
ΔH cyclohexa 135 triene = -360kJmol-1
ΔH Benzene = -208kJmol-1
Enthalpy change hydrogenation
χ
helliphellip
bull Benzene lower in energy by 150kJbull More stable due to delocalization of π electrons
150kJ-150
C-CSingle bond
C=CDouble bond
C=CBenzene
Bond lengthpm 154 134 140
Bond enthalpykJmol-1
346 614 507
3 Evidence for Benzene structure1
2
Click here evidence against Kekule
bull X ray hit benzene crystalbull Interact with electron (electron density
map) bull X ray diffraction producedbull Bond length measured
X ray crystallography
NO singledouble bond detected
3 Addition reaction for unsaturated C=C
Addition reaction
Substitution reaction
NO double bond
Acknowledgements
Thanks to source of pictures and video used in this presentation
Thanks to Creative Commons for excellent contribution on licenseshttpspaceplacenasagovgreenhouseenhttpwwwozonedepletioninfoeducationpart3ozonesourceshtmlhttpcreativecommonsorglicenseshttpwwwciesinorgdocs011-462011-462htmlhttpwwwepmagazineorgstorage165benzene-evidenceaspx
Prepared by Lawrence Kok
Check out more video tutorials from my site and hope you enjoy this tutorialhttplawrencekokblogspotcom
Ozone absorb UV radiation
Ozone absorb UV BC
O=O Double bond
O=O=OInter
mediate
Bond lengthpm 121 127
Bond enthalpykJ mol-1
498 364
Bond order 2 15
Dissociation by UV
lt242nm
lt330nm
Ozone weaker bondbullAbsorb UV AB(wavelength 330nm)
Bonding O2 and O3
Oxygen stronger bondbullAbsorb UV C (wavelength 230nm)
How ozone layer protect life on earth How Ozone
protect
Ozone absorb UV radiation
Ozone absorb UV BC
Ozone formation
O=O Double bond
O=O=OInter
mediate
Bond lengthpm 121 127
Bond enthalpykJ mol-1
498 364
Bond order 2 15
Dissociation by UV
lt242nm
lt330nm
Ozone weaker bondbullAbsorb UV AB(wavelength 330nm)
Bonding O2 and O3
Oxygen stronger bondbullAbsorb UV C (wavelength 230nm)
How ozone layer protect life on earth
Ozone Cycle
How Ozone
protect
Oxygen split by high UV to O (radical)
O radical combine to form ozone
1
2
3 Ozone (stratosphere) absorb UV BC
4Ozone reform again
Ozone createddestroyed by Chapman cycle
Oxygen reform again
Ozone absorb UV radiation
Ozone absorb UV BC
Ozone formation
O=O Double bond
O=O=OInter
mediate
Bond lengthpm 121 127
Bond enthalpykJ mol-1
498 364
Bond order 2 15
Dissociation by UV
lt242nm
lt330nm
Ozone weaker bondbullAbsorb UV AB(wavelength 330nm)
Bonding O2 and O3
Oxygen stronger bondbullAbsorb UV C (wavelength 230nm)
Free radical -reactive species with unpair electron
How ozone layer protect life on earth
Ozone Cycle
How Ozone
protect
Oxygen split by high UV to O (radical)
O radical combine to form ozone
1
2
3 Ozone (stratosphere) absorb UV BC
4Ozone reform again
Ozone cycle
Ozone createddestroyed by Chapman cycle
Oxygen reform again
Ozone absorb UV BC
CFC breaks down
How CFC breaks down
High UV BC
How CI radical destroy ozone
Catalytic destruction of ozone
Ozone Depleting Substances (ODS)
Carbon
Fluorine
Chlorine
Ozone absorb UV BC
CFC breaks down
How CFC breaks down
High UV BC
How CI radical destroy ozone
Catalytic destruction of ozone
Ozone Depleting Substances (ODS)
CI free radicals form
CImiddot react O3 form CIOmiddot radical
CIOmiddot react Omiddot form CImiddot radical again
Net eqn- ozone break down
Carbon
Fluorine
Chlorine
Ozone absorb UV BC
CFC breaks down
How CFC breaks down
High UV BC
How CI radical destroy ozone
Catalytic destruction of ozone
Ozone Depleting Substances (ODS)
How CFC destroys ozone
CI free radicals form
CImiddot react O3 form CIOmiddot radical
CIOmiddot react Omiddot form CImiddot radical again
Net eqn- ozone break down
Carbon
Fluorine
Chlorine
CI radical catalyzes again
Ozone absorb UV BC
How NO radical destroy ozone
Catalytic destruction of ozone
Ozone Depleting Substances (ODS)
Oxides of Nitrogen
Nitrogen Dioxide (NO2)
Nitrogen monoxide (nitric oxide NO)
Nitrous oxideN2O
Break down to form NO free radical (unpair electron)
+
Ozone absorb UV BC
NOx breaks down
How CFC breaks down
High UV BCHow NO radical destroy ozone
Catalytic destruction of ozone
Ozone Depleting Substances (ODS)
NO free radicals form
NO react O3 form NO2 radical
NO2 react O form NO radical again
Net eqn- ozone breaks down
Oxides of Nitrogen
Nitrogen Dioxide (NO2)
Nitrogen monoxide (nitric oxide NO)
Nitrous oxideN2O
Break down to form NO free radical (unpair electron)
NO NO2
NO2 NO + O2
+
Ozone absorb UV BC
NOx breaks down
How CFC breaks down
High UV BCHow NO radical destroy ozone
Catalytic destruction of ozone
Ozone Depleting Substances (ODS)
NO free radicals form
NO react O3 form NO2 radical
NO2 react O form NO radical again
Net eqn- ozone breaks down
Oxides of Nitrogen
Nitrogen Dioxide (NO2)
Nitrogen monoxide (nitric oxide NO)
Nitrous oxideN2O
Break down to form NO free radical (unpair electron)
NO NO2
NO2 NO + O2
Sources of NOx
Catalytic destruction of ozone
Ozone Depleting Substances (ODS)
Source of ODSbullHalogenated substancebullMan-made halocarbon refrigerant solvent propellantbullFoam-blowing agent (CFCs HCFCs freons halons)
Trichloroflouromethane CFC-11
Dichlorodifluoromethane CFC-12
Chlorodifluoromethane HCFC-22
Catalytic destruction of ozone
Ozone Depleting Substances (ODS)
Source of ODSbullHalogenated substancebullMan-made halocarbon refrigerant solvent propellantbullFoam-blowing agent (CFCs HCFCs freons halons)
CFCbullContain chlorine fluorine and carbon atomsbullExtremely stable with strong bonds long half lifebullStability allows CFC into the stratosphere bullHigh UV radiation reacts with CFCbullHigh UV photons breaks CFC (photochemical decomposition) bull Free Cl radicals form - destroying ozone
Trichloroflouromethane CFC-11
Dichlorodifluoromethane CFC-12
Chlorodifluoromethane HCFC-22
Why halogenate
d CFC used
Less harmful
Very harmful
Catalytic destruction of ozone
Ozone Depleting Substances (ODS)
Source of ODSbullHalogenated substancebullMan-made halocarbon refrigerant solvent propellantbullFoam-blowing agent (CFCs HCFCs freons halons)
Montreal Protocol bans CFC halon and ODS like carbon tetrachloride and trichloroethane
CFCbullContain chlorine fluorine and carbon atomsbullExtremely stable with strong bonds long half lifebullStability allows CFC into the stratosphere bullHigh UV radiation reacts with CFCbullHigh UV photons breaks CFC (photochemical decomposition) bull Free Cl radicals form - destroying ozone
Trichloroflouromethane CFC-11
Dichlorodifluoromethane CFC-12
Chlorodifluoromethane HCFC-22
Why halogenate
d CFC used
Less harmful
Very harmful
Why fluorinated is safer
Delocalization of electrons
Resonance bull Describing delocalization of electrons within a moleculepolyatomic ion where bonding cannot be express by ONE single Lewis structurebullDelocalization of π bond ndash π electrons spread over more than 2 nucleibullπ electrons are sharedbullπ electrons spread ndash more stable
Resonance structures benzene
Benzene6HC6
resonance structure 1 resonance structure 2
bull Unhybridised p orbitalbull Delocalization electrons above below planebull sp2 hybridization on carbon center
Delocalized electrons
Kekuleacute structure Cyclohexa- 135 triene
χ doublesingle bonds bet them
Benzene
Hexagonal planar
Kekule
Delocalization of electrons
Resonance bull Describing delocalization of electrons within a moleculepolyatomic ion where bonding cannot be express by ONE single Lewis structurebullDelocalization of π bond ndash π electrons spread over more than 2 nucleibullπ electrons are sharedbullπ electrons spread ndash more stable
Resonance structures benzene
Benzene6HC6
resonance structure 1 resonance structure 2
Resonance hybrid
bull All bonds C6H6 are identical in length strengthbull Hybrid of 2 resonance structuresbull No C-C (single) or C=C (double) bonds foundbull Only C ----- C bondbull Intermediate character bet singledouble bond
bull Bond Order =
bull Unhybridised p orbitalbull Delocalization electrons above below planebull sp2 hybridization on carbon center
15
Click here to view
Delocalized electrons
Kekuleacute structure Cyclohexa- 135 triene
χ doublesingle bonds bet them
Benzene
Hexagonal planar
Resonance Hybrid more stable than any of the resonance structure
Click here to view
Kekule
ResonanceDelocalization Energy
ΔH cyclohexene = -120kJmol-1
ΔH cyclohexa 13 diene = -240kJmol-1
ΔH cyclohexa 135 triene = -360kJmol-1
ΔH Benzene = -208kJmol-1
Enthalpy change hydrogenation
χ
helliphellip
bull Benzene lower in energy by 150kJbull More stable due to delocalization of π electrons
150kJ-150
3 Evidence for Benzene structure1
ResonanceDelocalization Energy
ΔH cyclohexene = -120kJmol-1
ΔH cyclohexa 13 diene = -240kJmol-1
ΔH cyclohexa 135 triene = -360kJmol-1
ΔH Benzene = -208kJmol-1
Enthalpy change hydrogenation
χ
helliphellip
bull Benzene lower in energy by 150kJbull More stable due to delocalization of π electrons
150kJ-150
C-CSingle bond
C=CDouble bond
C=CBenzene
Bond lengthpm 154 134 140
Bond enthalpykJmol-1
346 614 507
3 Evidence for Benzene structure1
2
bull X ray hit benzene crystalbull Interact with electron (electron density
map) bull X ray diffraction producedbull Bond length measured
X ray crystallography
NO singledouble bond detected
ResonanceDelocalization Energy
ΔH cyclohexene = -120kJmol-1
ΔH cyclohexa 13 diene = -240kJmol-1
ΔH cyclohexa 135 triene = -360kJmol-1
ΔH Benzene = -208kJmol-1
Enthalpy change hydrogenation
χ
helliphellip
bull Benzene lower in energy by 150kJbull More stable due to delocalization of π electrons
150kJ-150
C-CSingle bond
C=CDouble bond
C=CBenzene
Bond lengthpm 154 134 140
Bond enthalpykJmol-1
346 614 507
3 Evidence for Benzene structure1
2
Click here evidence against Kekule
bull X ray hit benzene crystalbull Interact with electron (electron density
map) bull X ray diffraction producedbull Bond length measured
X ray crystallography
NO singledouble bond detected
3 Addition reaction for unsaturated C=C
Addition reaction
Substitution reaction
NO double bond
Acknowledgements
Thanks to source of pictures and video used in this presentation
Thanks to Creative Commons for excellent contribution on licenseshttpspaceplacenasagovgreenhouseenhttpwwwozonedepletioninfoeducationpart3ozonesourceshtmlhttpcreativecommonsorglicenseshttpwwwciesinorgdocs011-462011-462htmlhttpwwwepmagazineorgstorage165benzene-evidenceaspx
Prepared by Lawrence Kok
Check out more video tutorials from my site and hope you enjoy this tutorialhttplawrencekokblogspotcom
Ozone absorb UV radiation
Ozone absorb UV BC
Ozone formation
O=O Double bond
O=O=OInter
mediate
Bond lengthpm 121 127
Bond enthalpykJ mol-1
498 364
Bond order 2 15
Dissociation by UV
lt242nm
lt330nm
Ozone weaker bondbullAbsorb UV AB(wavelength 330nm)
Bonding O2 and O3
Oxygen stronger bondbullAbsorb UV C (wavelength 230nm)
How ozone layer protect life on earth
Ozone Cycle
How Ozone
protect
Oxygen split by high UV to O (radical)
O radical combine to form ozone
1
2
3 Ozone (stratosphere) absorb UV BC
4Ozone reform again
Ozone createddestroyed by Chapman cycle
Oxygen reform again
Ozone absorb UV radiation
Ozone absorb UV BC
Ozone formation
O=O Double bond
O=O=OInter
mediate
Bond lengthpm 121 127
Bond enthalpykJ mol-1
498 364
Bond order 2 15
Dissociation by UV
lt242nm
lt330nm
Ozone weaker bondbullAbsorb UV AB(wavelength 330nm)
Bonding O2 and O3
Oxygen stronger bondbullAbsorb UV C (wavelength 230nm)
Free radical -reactive species with unpair electron
How ozone layer protect life on earth
Ozone Cycle
How Ozone
protect
Oxygen split by high UV to O (radical)
O radical combine to form ozone
1
2
3 Ozone (stratosphere) absorb UV BC
4Ozone reform again
Ozone cycle
Ozone createddestroyed by Chapman cycle
Oxygen reform again
Ozone absorb UV BC
CFC breaks down
How CFC breaks down
High UV BC
How CI radical destroy ozone
Catalytic destruction of ozone
Ozone Depleting Substances (ODS)
Carbon
Fluorine
Chlorine
Ozone absorb UV BC
CFC breaks down
How CFC breaks down
High UV BC
How CI radical destroy ozone
Catalytic destruction of ozone
Ozone Depleting Substances (ODS)
CI free radicals form
CImiddot react O3 form CIOmiddot radical
CIOmiddot react Omiddot form CImiddot radical again
Net eqn- ozone break down
Carbon
Fluorine
Chlorine
Ozone absorb UV BC
CFC breaks down
How CFC breaks down
High UV BC
How CI radical destroy ozone
Catalytic destruction of ozone
Ozone Depleting Substances (ODS)
How CFC destroys ozone
CI free radicals form
CImiddot react O3 form CIOmiddot radical
CIOmiddot react Omiddot form CImiddot radical again
Net eqn- ozone break down
Carbon
Fluorine
Chlorine
CI radical catalyzes again
Ozone absorb UV BC
How NO radical destroy ozone
Catalytic destruction of ozone
Ozone Depleting Substances (ODS)
Oxides of Nitrogen
Nitrogen Dioxide (NO2)
Nitrogen monoxide (nitric oxide NO)
Nitrous oxideN2O
Break down to form NO free radical (unpair electron)
+
Ozone absorb UV BC
NOx breaks down
How CFC breaks down
High UV BCHow NO radical destroy ozone
Catalytic destruction of ozone
Ozone Depleting Substances (ODS)
NO free radicals form
NO react O3 form NO2 radical
NO2 react O form NO radical again
Net eqn- ozone breaks down
Oxides of Nitrogen
Nitrogen Dioxide (NO2)
Nitrogen monoxide (nitric oxide NO)
Nitrous oxideN2O
Break down to form NO free radical (unpair electron)
NO NO2
NO2 NO + O2
+
Ozone absorb UV BC
NOx breaks down
How CFC breaks down
High UV BCHow NO radical destroy ozone
Catalytic destruction of ozone
Ozone Depleting Substances (ODS)
NO free radicals form
NO react O3 form NO2 radical
NO2 react O form NO radical again
Net eqn- ozone breaks down
Oxides of Nitrogen
Nitrogen Dioxide (NO2)
Nitrogen monoxide (nitric oxide NO)
Nitrous oxideN2O
Break down to form NO free radical (unpair electron)
NO NO2
NO2 NO + O2
Sources of NOx
Catalytic destruction of ozone
Ozone Depleting Substances (ODS)
Source of ODSbullHalogenated substancebullMan-made halocarbon refrigerant solvent propellantbullFoam-blowing agent (CFCs HCFCs freons halons)
Trichloroflouromethane CFC-11
Dichlorodifluoromethane CFC-12
Chlorodifluoromethane HCFC-22
Catalytic destruction of ozone
Ozone Depleting Substances (ODS)
Source of ODSbullHalogenated substancebullMan-made halocarbon refrigerant solvent propellantbullFoam-blowing agent (CFCs HCFCs freons halons)
CFCbullContain chlorine fluorine and carbon atomsbullExtremely stable with strong bonds long half lifebullStability allows CFC into the stratosphere bullHigh UV radiation reacts with CFCbullHigh UV photons breaks CFC (photochemical decomposition) bull Free Cl radicals form - destroying ozone
Trichloroflouromethane CFC-11
Dichlorodifluoromethane CFC-12
Chlorodifluoromethane HCFC-22
Why halogenate
d CFC used
Less harmful
Very harmful
Catalytic destruction of ozone
Ozone Depleting Substances (ODS)
Source of ODSbullHalogenated substancebullMan-made halocarbon refrigerant solvent propellantbullFoam-blowing agent (CFCs HCFCs freons halons)
Montreal Protocol bans CFC halon and ODS like carbon tetrachloride and trichloroethane
CFCbullContain chlorine fluorine and carbon atomsbullExtremely stable with strong bonds long half lifebullStability allows CFC into the stratosphere bullHigh UV radiation reacts with CFCbullHigh UV photons breaks CFC (photochemical decomposition) bull Free Cl radicals form - destroying ozone
Trichloroflouromethane CFC-11
Dichlorodifluoromethane CFC-12
Chlorodifluoromethane HCFC-22
Why halogenate
d CFC used
Less harmful
Very harmful
Why fluorinated is safer
Delocalization of electrons
Resonance bull Describing delocalization of electrons within a moleculepolyatomic ion where bonding cannot be express by ONE single Lewis structurebullDelocalization of π bond ndash π electrons spread over more than 2 nucleibullπ electrons are sharedbullπ electrons spread ndash more stable
Resonance structures benzene
Benzene6HC6
resonance structure 1 resonance structure 2
bull Unhybridised p orbitalbull Delocalization electrons above below planebull sp2 hybridization on carbon center
Delocalized electrons
Kekuleacute structure Cyclohexa- 135 triene
χ doublesingle bonds bet them
Benzene
Hexagonal planar
Kekule
Delocalization of electrons
Resonance bull Describing delocalization of electrons within a moleculepolyatomic ion where bonding cannot be express by ONE single Lewis structurebullDelocalization of π bond ndash π electrons spread over more than 2 nucleibullπ electrons are sharedbullπ electrons spread ndash more stable
Resonance structures benzene
Benzene6HC6
resonance structure 1 resonance structure 2
Resonance hybrid
bull All bonds C6H6 are identical in length strengthbull Hybrid of 2 resonance structuresbull No C-C (single) or C=C (double) bonds foundbull Only C ----- C bondbull Intermediate character bet singledouble bond
bull Bond Order =
bull Unhybridised p orbitalbull Delocalization electrons above below planebull sp2 hybridization on carbon center
15
Click here to view
Delocalized electrons
Kekuleacute structure Cyclohexa- 135 triene
χ doublesingle bonds bet them
Benzene
Hexagonal planar
Resonance Hybrid more stable than any of the resonance structure
Click here to view
Kekule
ResonanceDelocalization Energy
ΔH cyclohexene = -120kJmol-1
ΔH cyclohexa 13 diene = -240kJmol-1
ΔH cyclohexa 135 triene = -360kJmol-1
ΔH Benzene = -208kJmol-1
Enthalpy change hydrogenation
χ
helliphellip
bull Benzene lower in energy by 150kJbull More stable due to delocalization of π electrons
150kJ-150
3 Evidence for Benzene structure1
ResonanceDelocalization Energy
ΔH cyclohexene = -120kJmol-1
ΔH cyclohexa 13 diene = -240kJmol-1
ΔH cyclohexa 135 triene = -360kJmol-1
ΔH Benzene = -208kJmol-1
Enthalpy change hydrogenation
χ
helliphellip
bull Benzene lower in energy by 150kJbull More stable due to delocalization of π electrons
150kJ-150
C-CSingle bond
C=CDouble bond
C=CBenzene
Bond lengthpm 154 134 140
Bond enthalpykJmol-1
346 614 507
3 Evidence for Benzene structure1
2
bull X ray hit benzene crystalbull Interact with electron (electron density
map) bull X ray diffraction producedbull Bond length measured
X ray crystallography
NO singledouble bond detected
ResonanceDelocalization Energy
ΔH cyclohexene = -120kJmol-1
ΔH cyclohexa 13 diene = -240kJmol-1
ΔH cyclohexa 135 triene = -360kJmol-1
ΔH Benzene = -208kJmol-1
Enthalpy change hydrogenation
χ
helliphellip
bull Benzene lower in energy by 150kJbull More stable due to delocalization of π electrons
150kJ-150
C-CSingle bond
C=CDouble bond
C=CBenzene
Bond lengthpm 154 134 140
Bond enthalpykJmol-1
346 614 507
3 Evidence for Benzene structure1
2
Click here evidence against Kekule
bull X ray hit benzene crystalbull Interact with electron (electron density
map) bull X ray diffraction producedbull Bond length measured
X ray crystallography
NO singledouble bond detected
3 Addition reaction for unsaturated C=C
Addition reaction
Substitution reaction
NO double bond
Acknowledgements
Thanks to source of pictures and video used in this presentation
Thanks to Creative Commons for excellent contribution on licenseshttpspaceplacenasagovgreenhouseenhttpwwwozonedepletioninfoeducationpart3ozonesourceshtmlhttpcreativecommonsorglicenseshttpwwwciesinorgdocs011-462011-462htmlhttpwwwepmagazineorgstorage165benzene-evidenceaspx
Prepared by Lawrence Kok
Check out more video tutorials from my site and hope you enjoy this tutorialhttplawrencekokblogspotcom
Ozone absorb UV radiation
Ozone absorb UV BC
Ozone formation
O=O Double bond
O=O=OInter
mediate
Bond lengthpm 121 127
Bond enthalpykJ mol-1
498 364
Bond order 2 15
Dissociation by UV
lt242nm
lt330nm
Ozone weaker bondbullAbsorb UV AB(wavelength 330nm)
Bonding O2 and O3
Oxygen stronger bondbullAbsorb UV C (wavelength 230nm)
Free radical -reactive species with unpair electron
How ozone layer protect life on earth
Ozone Cycle
How Ozone
protect
Oxygen split by high UV to O (radical)
O radical combine to form ozone
1
2
3 Ozone (stratosphere) absorb UV BC
4Ozone reform again
Ozone cycle
Ozone createddestroyed by Chapman cycle
Oxygen reform again
Ozone absorb UV BC
CFC breaks down
How CFC breaks down
High UV BC
How CI radical destroy ozone
Catalytic destruction of ozone
Ozone Depleting Substances (ODS)
Carbon
Fluorine
Chlorine
Ozone absorb UV BC
CFC breaks down
How CFC breaks down
High UV BC
How CI radical destroy ozone
Catalytic destruction of ozone
Ozone Depleting Substances (ODS)
CI free radicals form
CImiddot react O3 form CIOmiddot radical
CIOmiddot react Omiddot form CImiddot radical again
Net eqn- ozone break down
Carbon
Fluorine
Chlorine
Ozone absorb UV BC
CFC breaks down
How CFC breaks down
High UV BC
How CI radical destroy ozone
Catalytic destruction of ozone
Ozone Depleting Substances (ODS)
How CFC destroys ozone
CI free radicals form
CImiddot react O3 form CIOmiddot radical
CIOmiddot react Omiddot form CImiddot radical again
Net eqn- ozone break down
Carbon
Fluorine
Chlorine
CI radical catalyzes again
Ozone absorb UV BC
How NO radical destroy ozone
Catalytic destruction of ozone
Ozone Depleting Substances (ODS)
Oxides of Nitrogen
Nitrogen Dioxide (NO2)
Nitrogen monoxide (nitric oxide NO)
Nitrous oxideN2O
Break down to form NO free radical (unpair electron)
+
Ozone absorb UV BC
NOx breaks down
How CFC breaks down
High UV BCHow NO radical destroy ozone
Catalytic destruction of ozone
Ozone Depleting Substances (ODS)
NO free radicals form
NO react O3 form NO2 radical
NO2 react O form NO radical again
Net eqn- ozone breaks down
Oxides of Nitrogen
Nitrogen Dioxide (NO2)
Nitrogen monoxide (nitric oxide NO)
Nitrous oxideN2O
Break down to form NO free radical (unpair electron)
NO NO2
NO2 NO + O2
+
Ozone absorb UV BC
NOx breaks down
How CFC breaks down
High UV BCHow NO radical destroy ozone
Catalytic destruction of ozone
Ozone Depleting Substances (ODS)
NO free radicals form
NO react O3 form NO2 radical
NO2 react O form NO radical again
Net eqn- ozone breaks down
Oxides of Nitrogen
Nitrogen Dioxide (NO2)
Nitrogen monoxide (nitric oxide NO)
Nitrous oxideN2O
Break down to form NO free radical (unpair electron)
NO NO2
NO2 NO + O2
Sources of NOx
Catalytic destruction of ozone
Ozone Depleting Substances (ODS)
Source of ODSbullHalogenated substancebullMan-made halocarbon refrigerant solvent propellantbullFoam-blowing agent (CFCs HCFCs freons halons)
Trichloroflouromethane CFC-11
Dichlorodifluoromethane CFC-12
Chlorodifluoromethane HCFC-22
Catalytic destruction of ozone
Ozone Depleting Substances (ODS)
Source of ODSbullHalogenated substancebullMan-made halocarbon refrigerant solvent propellantbullFoam-blowing agent (CFCs HCFCs freons halons)
CFCbullContain chlorine fluorine and carbon atomsbullExtremely stable with strong bonds long half lifebullStability allows CFC into the stratosphere bullHigh UV radiation reacts with CFCbullHigh UV photons breaks CFC (photochemical decomposition) bull Free Cl radicals form - destroying ozone
Trichloroflouromethane CFC-11
Dichlorodifluoromethane CFC-12
Chlorodifluoromethane HCFC-22
Why halogenate
d CFC used
Less harmful
Very harmful
Catalytic destruction of ozone
Ozone Depleting Substances (ODS)
Source of ODSbullHalogenated substancebullMan-made halocarbon refrigerant solvent propellantbullFoam-blowing agent (CFCs HCFCs freons halons)
Montreal Protocol bans CFC halon and ODS like carbon tetrachloride and trichloroethane
CFCbullContain chlorine fluorine and carbon atomsbullExtremely stable with strong bonds long half lifebullStability allows CFC into the stratosphere bullHigh UV radiation reacts with CFCbullHigh UV photons breaks CFC (photochemical decomposition) bull Free Cl radicals form - destroying ozone
Trichloroflouromethane CFC-11
Dichlorodifluoromethane CFC-12
Chlorodifluoromethane HCFC-22
Why halogenate
d CFC used
Less harmful
Very harmful
Why fluorinated is safer
Delocalization of electrons
Resonance bull Describing delocalization of electrons within a moleculepolyatomic ion where bonding cannot be express by ONE single Lewis structurebullDelocalization of π bond ndash π electrons spread over more than 2 nucleibullπ electrons are sharedbullπ electrons spread ndash more stable
Resonance structures benzene
Benzene6HC6
resonance structure 1 resonance structure 2
bull Unhybridised p orbitalbull Delocalization electrons above below planebull sp2 hybridization on carbon center
Delocalized electrons
Kekuleacute structure Cyclohexa- 135 triene
χ doublesingle bonds bet them
Benzene
Hexagonal planar
Kekule
Delocalization of electrons
Resonance bull Describing delocalization of electrons within a moleculepolyatomic ion where bonding cannot be express by ONE single Lewis structurebullDelocalization of π bond ndash π electrons spread over more than 2 nucleibullπ electrons are sharedbullπ electrons spread ndash more stable
Resonance structures benzene
Benzene6HC6
resonance structure 1 resonance structure 2
Resonance hybrid
bull All bonds C6H6 are identical in length strengthbull Hybrid of 2 resonance structuresbull No C-C (single) or C=C (double) bonds foundbull Only C ----- C bondbull Intermediate character bet singledouble bond
bull Bond Order =
bull Unhybridised p orbitalbull Delocalization electrons above below planebull sp2 hybridization on carbon center
15
Click here to view
Delocalized electrons
Kekuleacute structure Cyclohexa- 135 triene
χ doublesingle bonds bet them
Benzene
Hexagonal planar
Resonance Hybrid more stable than any of the resonance structure
Click here to view
Kekule
ResonanceDelocalization Energy
ΔH cyclohexene = -120kJmol-1
ΔH cyclohexa 13 diene = -240kJmol-1
ΔH cyclohexa 135 triene = -360kJmol-1
ΔH Benzene = -208kJmol-1
Enthalpy change hydrogenation
χ
helliphellip
bull Benzene lower in energy by 150kJbull More stable due to delocalization of π electrons
150kJ-150
3 Evidence for Benzene structure1
ResonanceDelocalization Energy
ΔH cyclohexene = -120kJmol-1
ΔH cyclohexa 13 diene = -240kJmol-1
ΔH cyclohexa 135 triene = -360kJmol-1
ΔH Benzene = -208kJmol-1
Enthalpy change hydrogenation
χ
helliphellip
bull Benzene lower in energy by 150kJbull More stable due to delocalization of π electrons
150kJ-150
C-CSingle bond
C=CDouble bond
C=CBenzene
Bond lengthpm 154 134 140
Bond enthalpykJmol-1
346 614 507
3 Evidence for Benzene structure1
2
bull X ray hit benzene crystalbull Interact with electron (electron density
map) bull X ray diffraction producedbull Bond length measured
X ray crystallography
NO singledouble bond detected
ResonanceDelocalization Energy
ΔH cyclohexene = -120kJmol-1
ΔH cyclohexa 13 diene = -240kJmol-1
ΔH cyclohexa 135 triene = -360kJmol-1
ΔH Benzene = -208kJmol-1
Enthalpy change hydrogenation
χ
helliphellip
bull Benzene lower in energy by 150kJbull More stable due to delocalization of π electrons
150kJ-150
C-CSingle bond
C=CDouble bond
C=CBenzene
Bond lengthpm 154 134 140
Bond enthalpykJmol-1
346 614 507
3 Evidence for Benzene structure1
2
Click here evidence against Kekule
bull X ray hit benzene crystalbull Interact with electron (electron density
map) bull X ray diffraction producedbull Bond length measured
X ray crystallography
NO singledouble bond detected
3 Addition reaction for unsaturated C=C
Addition reaction
Substitution reaction
NO double bond
Acknowledgements
Thanks to source of pictures and video used in this presentation
Thanks to Creative Commons for excellent contribution on licenseshttpspaceplacenasagovgreenhouseenhttpwwwozonedepletioninfoeducationpart3ozonesourceshtmlhttpcreativecommonsorglicenseshttpwwwciesinorgdocs011-462011-462htmlhttpwwwepmagazineorgstorage165benzene-evidenceaspx
Prepared by Lawrence Kok
Check out more video tutorials from my site and hope you enjoy this tutorialhttplawrencekokblogspotcom
Ozone absorb UV BC
CFC breaks down
How CFC breaks down
High UV BC
How CI radical destroy ozone
Catalytic destruction of ozone
Ozone Depleting Substances (ODS)
Carbon
Fluorine
Chlorine
Ozone absorb UV BC
CFC breaks down
How CFC breaks down
High UV BC
How CI radical destroy ozone
Catalytic destruction of ozone
Ozone Depleting Substances (ODS)
CI free radicals form
CImiddot react O3 form CIOmiddot radical
CIOmiddot react Omiddot form CImiddot radical again
Net eqn- ozone break down
Carbon
Fluorine
Chlorine
Ozone absorb UV BC
CFC breaks down
How CFC breaks down
High UV BC
How CI radical destroy ozone
Catalytic destruction of ozone
Ozone Depleting Substances (ODS)
How CFC destroys ozone
CI free radicals form
CImiddot react O3 form CIOmiddot radical
CIOmiddot react Omiddot form CImiddot radical again
Net eqn- ozone break down
Carbon
Fluorine
Chlorine
CI radical catalyzes again
Ozone absorb UV BC
How NO radical destroy ozone
Catalytic destruction of ozone
Ozone Depleting Substances (ODS)
Oxides of Nitrogen
Nitrogen Dioxide (NO2)
Nitrogen monoxide (nitric oxide NO)
Nitrous oxideN2O
Break down to form NO free radical (unpair electron)
+
Ozone absorb UV BC
NOx breaks down
How CFC breaks down
High UV BCHow NO radical destroy ozone
Catalytic destruction of ozone
Ozone Depleting Substances (ODS)
NO free radicals form
NO react O3 form NO2 radical
NO2 react O form NO radical again
Net eqn- ozone breaks down
Oxides of Nitrogen
Nitrogen Dioxide (NO2)
Nitrogen monoxide (nitric oxide NO)
Nitrous oxideN2O
Break down to form NO free radical (unpair electron)
NO NO2
NO2 NO + O2
+
Ozone absorb UV BC
NOx breaks down
How CFC breaks down
High UV BCHow NO radical destroy ozone
Catalytic destruction of ozone
Ozone Depleting Substances (ODS)
NO free radicals form
NO react O3 form NO2 radical
NO2 react O form NO radical again
Net eqn- ozone breaks down
Oxides of Nitrogen
Nitrogen Dioxide (NO2)
Nitrogen monoxide (nitric oxide NO)
Nitrous oxideN2O
Break down to form NO free radical (unpair electron)
NO NO2
NO2 NO + O2
Sources of NOx
Catalytic destruction of ozone
Ozone Depleting Substances (ODS)
Source of ODSbullHalogenated substancebullMan-made halocarbon refrigerant solvent propellantbullFoam-blowing agent (CFCs HCFCs freons halons)
Trichloroflouromethane CFC-11
Dichlorodifluoromethane CFC-12
Chlorodifluoromethane HCFC-22
Catalytic destruction of ozone
Ozone Depleting Substances (ODS)
Source of ODSbullHalogenated substancebullMan-made halocarbon refrigerant solvent propellantbullFoam-blowing agent (CFCs HCFCs freons halons)
CFCbullContain chlorine fluorine and carbon atomsbullExtremely stable with strong bonds long half lifebullStability allows CFC into the stratosphere bullHigh UV radiation reacts with CFCbullHigh UV photons breaks CFC (photochemical decomposition) bull Free Cl radicals form - destroying ozone
Trichloroflouromethane CFC-11
Dichlorodifluoromethane CFC-12
Chlorodifluoromethane HCFC-22
Why halogenate
d CFC used
Less harmful
Very harmful
Catalytic destruction of ozone
Ozone Depleting Substances (ODS)
Source of ODSbullHalogenated substancebullMan-made halocarbon refrigerant solvent propellantbullFoam-blowing agent (CFCs HCFCs freons halons)
Montreal Protocol bans CFC halon and ODS like carbon tetrachloride and trichloroethane
CFCbullContain chlorine fluorine and carbon atomsbullExtremely stable with strong bonds long half lifebullStability allows CFC into the stratosphere bullHigh UV radiation reacts with CFCbullHigh UV photons breaks CFC (photochemical decomposition) bull Free Cl radicals form - destroying ozone
Trichloroflouromethane CFC-11
Dichlorodifluoromethane CFC-12
Chlorodifluoromethane HCFC-22
Why halogenate
d CFC used
Less harmful
Very harmful
Why fluorinated is safer
Delocalization of electrons
Resonance bull Describing delocalization of electrons within a moleculepolyatomic ion where bonding cannot be express by ONE single Lewis structurebullDelocalization of π bond ndash π electrons spread over more than 2 nucleibullπ electrons are sharedbullπ electrons spread ndash more stable
Resonance structures benzene
Benzene6HC6
resonance structure 1 resonance structure 2
bull Unhybridised p orbitalbull Delocalization electrons above below planebull sp2 hybridization on carbon center
Delocalized electrons
Kekuleacute structure Cyclohexa- 135 triene
χ doublesingle bonds bet them
Benzene
Hexagonal planar
Kekule
Delocalization of electrons
Resonance bull Describing delocalization of electrons within a moleculepolyatomic ion where bonding cannot be express by ONE single Lewis structurebullDelocalization of π bond ndash π electrons spread over more than 2 nucleibullπ electrons are sharedbullπ electrons spread ndash more stable
Resonance structures benzene
Benzene6HC6
resonance structure 1 resonance structure 2
Resonance hybrid
bull All bonds C6H6 are identical in length strengthbull Hybrid of 2 resonance structuresbull No C-C (single) or C=C (double) bonds foundbull Only C ----- C bondbull Intermediate character bet singledouble bond
bull Bond Order =
bull Unhybridised p orbitalbull Delocalization electrons above below planebull sp2 hybridization on carbon center
15
Click here to view
Delocalized electrons
Kekuleacute structure Cyclohexa- 135 triene
χ doublesingle bonds bet them
Benzene
Hexagonal planar
Resonance Hybrid more stable than any of the resonance structure
Click here to view
Kekule
ResonanceDelocalization Energy
ΔH cyclohexene = -120kJmol-1
ΔH cyclohexa 13 diene = -240kJmol-1
ΔH cyclohexa 135 triene = -360kJmol-1
ΔH Benzene = -208kJmol-1
Enthalpy change hydrogenation
χ
helliphellip
bull Benzene lower in energy by 150kJbull More stable due to delocalization of π electrons
150kJ-150
3 Evidence for Benzene structure1
ResonanceDelocalization Energy
ΔH cyclohexene = -120kJmol-1
ΔH cyclohexa 13 diene = -240kJmol-1
ΔH cyclohexa 135 triene = -360kJmol-1
ΔH Benzene = -208kJmol-1
Enthalpy change hydrogenation
χ
helliphellip
bull Benzene lower in energy by 150kJbull More stable due to delocalization of π electrons
150kJ-150
C-CSingle bond
C=CDouble bond
C=CBenzene
Bond lengthpm 154 134 140
Bond enthalpykJmol-1
346 614 507
3 Evidence for Benzene structure1
2
bull X ray hit benzene crystalbull Interact with electron (electron density
map) bull X ray diffraction producedbull Bond length measured
X ray crystallography
NO singledouble bond detected
ResonanceDelocalization Energy
ΔH cyclohexene = -120kJmol-1
ΔH cyclohexa 13 diene = -240kJmol-1
ΔH cyclohexa 135 triene = -360kJmol-1
ΔH Benzene = -208kJmol-1
Enthalpy change hydrogenation
χ
helliphellip
bull Benzene lower in energy by 150kJbull More stable due to delocalization of π electrons
150kJ-150
C-CSingle bond
C=CDouble bond
C=CBenzene
Bond lengthpm 154 134 140
Bond enthalpykJmol-1
346 614 507
3 Evidence for Benzene structure1
2
Click here evidence against Kekule
bull X ray hit benzene crystalbull Interact with electron (electron density
map) bull X ray diffraction producedbull Bond length measured
X ray crystallography
NO singledouble bond detected
3 Addition reaction for unsaturated C=C
Addition reaction
Substitution reaction
NO double bond
Acknowledgements
Thanks to source of pictures and video used in this presentation
Thanks to Creative Commons for excellent contribution on licenseshttpspaceplacenasagovgreenhouseenhttpwwwozonedepletioninfoeducationpart3ozonesourceshtmlhttpcreativecommonsorglicenseshttpwwwciesinorgdocs011-462011-462htmlhttpwwwepmagazineorgstorage165benzene-evidenceaspx
Prepared by Lawrence Kok
Check out more video tutorials from my site and hope you enjoy this tutorialhttplawrencekokblogspotcom
Ozone absorb UV BC
CFC breaks down
How CFC breaks down
High UV BC
How CI radical destroy ozone
Catalytic destruction of ozone
Ozone Depleting Substances (ODS)
CI free radicals form
CImiddot react O3 form CIOmiddot radical
CIOmiddot react Omiddot form CImiddot radical again
Net eqn- ozone break down
Carbon
Fluorine
Chlorine
Ozone absorb UV BC
CFC breaks down
How CFC breaks down
High UV BC
How CI radical destroy ozone
Catalytic destruction of ozone
Ozone Depleting Substances (ODS)
How CFC destroys ozone
CI free radicals form
CImiddot react O3 form CIOmiddot radical
CIOmiddot react Omiddot form CImiddot radical again
Net eqn- ozone break down
Carbon
Fluorine
Chlorine
CI radical catalyzes again
Ozone absorb UV BC
How NO radical destroy ozone
Catalytic destruction of ozone
Ozone Depleting Substances (ODS)
Oxides of Nitrogen
Nitrogen Dioxide (NO2)
Nitrogen monoxide (nitric oxide NO)
Nitrous oxideN2O
Break down to form NO free radical (unpair electron)
+
Ozone absorb UV BC
NOx breaks down
How CFC breaks down
High UV BCHow NO radical destroy ozone
Catalytic destruction of ozone
Ozone Depleting Substances (ODS)
NO free radicals form
NO react O3 form NO2 radical
NO2 react O form NO radical again
Net eqn- ozone breaks down
Oxides of Nitrogen
Nitrogen Dioxide (NO2)
Nitrogen monoxide (nitric oxide NO)
Nitrous oxideN2O
Break down to form NO free radical (unpair electron)
NO NO2
NO2 NO + O2
+
Ozone absorb UV BC
NOx breaks down
How CFC breaks down
High UV BCHow NO radical destroy ozone
Catalytic destruction of ozone
Ozone Depleting Substances (ODS)
NO free radicals form
NO react O3 form NO2 radical
NO2 react O form NO radical again
Net eqn- ozone breaks down
Oxides of Nitrogen
Nitrogen Dioxide (NO2)
Nitrogen monoxide (nitric oxide NO)
Nitrous oxideN2O
Break down to form NO free radical (unpair electron)
NO NO2
NO2 NO + O2
Sources of NOx
Catalytic destruction of ozone
Ozone Depleting Substances (ODS)
Source of ODSbullHalogenated substancebullMan-made halocarbon refrigerant solvent propellantbullFoam-blowing agent (CFCs HCFCs freons halons)
Trichloroflouromethane CFC-11
Dichlorodifluoromethane CFC-12
Chlorodifluoromethane HCFC-22
Catalytic destruction of ozone
Ozone Depleting Substances (ODS)
Source of ODSbullHalogenated substancebullMan-made halocarbon refrigerant solvent propellantbullFoam-blowing agent (CFCs HCFCs freons halons)
CFCbullContain chlorine fluorine and carbon atomsbullExtremely stable with strong bonds long half lifebullStability allows CFC into the stratosphere bullHigh UV radiation reacts with CFCbullHigh UV photons breaks CFC (photochemical decomposition) bull Free Cl radicals form - destroying ozone
Trichloroflouromethane CFC-11
Dichlorodifluoromethane CFC-12
Chlorodifluoromethane HCFC-22
Why halogenate
d CFC used
Less harmful
Very harmful
Catalytic destruction of ozone
Ozone Depleting Substances (ODS)
Source of ODSbullHalogenated substancebullMan-made halocarbon refrigerant solvent propellantbullFoam-blowing agent (CFCs HCFCs freons halons)
Montreal Protocol bans CFC halon and ODS like carbon tetrachloride and trichloroethane
CFCbullContain chlorine fluorine and carbon atomsbullExtremely stable with strong bonds long half lifebullStability allows CFC into the stratosphere bullHigh UV radiation reacts with CFCbullHigh UV photons breaks CFC (photochemical decomposition) bull Free Cl radicals form - destroying ozone
Trichloroflouromethane CFC-11
Dichlorodifluoromethane CFC-12
Chlorodifluoromethane HCFC-22
Why halogenate
d CFC used
Less harmful
Very harmful
Why fluorinated is safer
Delocalization of electrons
Resonance bull Describing delocalization of electrons within a moleculepolyatomic ion where bonding cannot be express by ONE single Lewis structurebullDelocalization of π bond ndash π electrons spread over more than 2 nucleibullπ electrons are sharedbullπ electrons spread ndash more stable
Resonance structures benzene
Benzene6HC6
resonance structure 1 resonance structure 2
bull Unhybridised p orbitalbull Delocalization electrons above below planebull sp2 hybridization on carbon center
Delocalized electrons
Kekuleacute structure Cyclohexa- 135 triene
χ doublesingle bonds bet them
Benzene
Hexagonal planar
Kekule
Delocalization of electrons
Resonance bull Describing delocalization of electrons within a moleculepolyatomic ion where bonding cannot be express by ONE single Lewis structurebullDelocalization of π bond ndash π electrons spread over more than 2 nucleibullπ electrons are sharedbullπ electrons spread ndash more stable
Resonance structures benzene
Benzene6HC6
resonance structure 1 resonance structure 2
Resonance hybrid
bull All bonds C6H6 are identical in length strengthbull Hybrid of 2 resonance structuresbull No C-C (single) or C=C (double) bonds foundbull Only C ----- C bondbull Intermediate character bet singledouble bond
bull Bond Order =
bull Unhybridised p orbitalbull Delocalization electrons above below planebull sp2 hybridization on carbon center
15
Click here to view
Delocalized electrons
Kekuleacute structure Cyclohexa- 135 triene
χ doublesingle bonds bet them
Benzene
Hexagonal planar
Resonance Hybrid more stable than any of the resonance structure
Click here to view
Kekule
ResonanceDelocalization Energy
ΔH cyclohexene = -120kJmol-1
ΔH cyclohexa 13 diene = -240kJmol-1
ΔH cyclohexa 135 triene = -360kJmol-1
ΔH Benzene = -208kJmol-1
Enthalpy change hydrogenation
χ
helliphellip
bull Benzene lower in energy by 150kJbull More stable due to delocalization of π electrons
150kJ-150
3 Evidence for Benzene structure1
ResonanceDelocalization Energy
ΔH cyclohexene = -120kJmol-1
ΔH cyclohexa 13 diene = -240kJmol-1
ΔH cyclohexa 135 triene = -360kJmol-1
ΔH Benzene = -208kJmol-1
Enthalpy change hydrogenation
χ
helliphellip
bull Benzene lower in energy by 150kJbull More stable due to delocalization of π electrons
150kJ-150
C-CSingle bond
C=CDouble bond
C=CBenzene
Bond lengthpm 154 134 140
Bond enthalpykJmol-1
346 614 507
3 Evidence for Benzene structure1
2
bull X ray hit benzene crystalbull Interact with electron (electron density
map) bull X ray diffraction producedbull Bond length measured
X ray crystallography
NO singledouble bond detected
ResonanceDelocalization Energy
ΔH cyclohexene = -120kJmol-1
ΔH cyclohexa 13 diene = -240kJmol-1
ΔH cyclohexa 135 triene = -360kJmol-1
ΔH Benzene = -208kJmol-1
Enthalpy change hydrogenation
χ
helliphellip
bull Benzene lower in energy by 150kJbull More stable due to delocalization of π electrons
150kJ-150
C-CSingle bond
C=CDouble bond
C=CBenzene
Bond lengthpm 154 134 140
Bond enthalpykJmol-1
346 614 507
3 Evidence for Benzene structure1
2
Click here evidence against Kekule
bull X ray hit benzene crystalbull Interact with electron (electron density
map) bull X ray diffraction producedbull Bond length measured
X ray crystallography
NO singledouble bond detected
3 Addition reaction for unsaturated C=C
Addition reaction
Substitution reaction
NO double bond
Acknowledgements
Thanks to source of pictures and video used in this presentation
Thanks to Creative Commons for excellent contribution on licenseshttpspaceplacenasagovgreenhouseenhttpwwwozonedepletioninfoeducationpart3ozonesourceshtmlhttpcreativecommonsorglicenseshttpwwwciesinorgdocs011-462011-462htmlhttpwwwepmagazineorgstorage165benzene-evidenceaspx
Prepared by Lawrence Kok
Check out more video tutorials from my site and hope you enjoy this tutorialhttplawrencekokblogspotcom
Ozone absorb UV BC
CFC breaks down
How CFC breaks down
High UV BC
How CI radical destroy ozone
Catalytic destruction of ozone
Ozone Depleting Substances (ODS)
How CFC destroys ozone
CI free radicals form
CImiddot react O3 form CIOmiddot radical
CIOmiddot react Omiddot form CImiddot radical again
Net eqn- ozone break down
Carbon
Fluorine
Chlorine
CI radical catalyzes again
Ozone absorb UV BC
How NO radical destroy ozone
Catalytic destruction of ozone
Ozone Depleting Substances (ODS)
Oxides of Nitrogen
Nitrogen Dioxide (NO2)
Nitrogen monoxide (nitric oxide NO)
Nitrous oxideN2O
Break down to form NO free radical (unpair electron)
+
Ozone absorb UV BC
NOx breaks down
How CFC breaks down
High UV BCHow NO radical destroy ozone
Catalytic destruction of ozone
Ozone Depleting Substances (ODS)
NO free radicals form
NO react O3 form NO2 radical
NO2 react O form NO radical again
Net eqn- ozone breaks down
Oxides of Nitrogen
Nitrogen Dioxide (NO2)
Nitrogen monoxide (nitric oxide NO)
Nitrous oxideN2O
Break down to form NO free radical (unpair electron)
NO NO2
NO2 NO + O2
+
Ozone absorb UV BC
NOx breaks down
How CFC breaks down
High UV BCHow NO radical destroy ozone
Catalytic destruction of ozone
Ozone Depleting Substances (ODS)
NO free radicals form
NO react O3 form NO2 radical
NO2 react O form NO radical again
Net eqn- ozone breaks down
Oxides of Nitrogen
Nitrogen Dioxide (NO2)
Nitrogen monoxide (nitric oxide NO)
Nitrous oxideN2O
Break down to form NO free radical (unpair electron)
NO NO2
NO2 NO + O2
Sources of NOx
Catalytic destruction of ozone
Ozone Depleting Substances (ODS)
Source of ODSbullHalogenated substancebullMan-made halocarbon refrigerant solvent propellantbullFoam-blowing agent (CFCs HCFCs freons halons)
Trichloroflouromethane CFC-11
Dichlorodifluoromethane CFC-12
Chlorodifluoromethane HCFC-22
Catalytic destruction of ozone
Ozone Depleting Substances (ODS)
Source of ODSbullHalogenated substancebullMan-made halocarbon refrigerant solvent propellantbullFoam-blowing agent (CFCs HCFCs freons halons)
CFCbullContain chlorine fluorine and carbon atomsbullExtremely stable with strong bonds long half lifebullStability allows CFC into the stratosphere bullHigh UV radiation reacts with CFCbullHigh UV photons breaks CFC (photochemical decomposition) bull Free Cl radicals form - destroying ozone
Trichloroflouromethane CFC-11
Dichlorodifluoromethane CFC-12
Chlorodifluoromethane HCFC-22
Why halogenate
d CFC used
Less harmful
Very harmful
Catalytic destruction of ozone
Ozone Depleting Substances (ODS)
Source of ODSbullHalogenated substancebullMan-made halocarbon refrigerant solvent propellantbullFoam-blowing agent (CFCs HCFCs freons halons)
Montreal Protocol bans CFC halon and ODS like carbon tetrachloride and trichloroethane
CFCbullContain chlorine fluorine and carbon atomsbullExtremely stable with strong bonds long half lifebullStability allows CFC into the stratosphere bullHigh UV radiation reacts with CFCbullHigh UV photons breaks CFC (photochemical decomposition) bull Free Cl radicals form - destroying ozone
Trichloroflouromethane CFC-11
Dichlorodifluoromethane CFC-12
Chlorodifluoromethane HCFC-22
Why halogenate
d CFC used
Less harmful
Very harmful
Why fluorinated is safer
Delocalization of electrons
Resonance bull Describing delocalization of electrons within a moleculepolyatomic ion where bonding cannot be express by ONE single Lewis structurebullDelocalization of π bond ndash π electrons spread over more than 2 nucleibullπ electrons are sharedbullπ electrons spread ndash more stable
Resonance structures benzene
Benzene6HC6
resonance structure 1 resonance structure 2
bull Unhybridised p orbitalbull Delocalization electrons above below planebull sp2 hybridization on carbon center
Delocalized electrons
Kekuleacute structure Cyclohexa- 135 triene
χ doublesingle bonds bet them
Benzene
Hexagonal planar
Kekule
Delocalization of electrons
Resonance bull Describing delocalization of electrons within a moleculepolyatomic ion where bonding cannot be express by ONE single Lewis structurebullDelocalization of π bond ndash π electrons spread over more than 2 nucleibullπ electrons are sharedbullπ electrons spread ndash more stable
Resonance structures benzene
Benzene6HC6
resonance structure 1 resonance structure 2
Resonance hybrid
bull All bonds C6H6 are identical in length strengthbull Hybrid of 2 resonance structuresbull No C-C (single) or C=C (double) bonds foundbull Only C ----- C bondbull Intermediate character bet singledouble bond
bull Bond Order =
bull Unhybridised p orbitalbull Delocalization electrons above below planebull sp2 hybridization on carbon center
15
Click here to view
Delocalized electrons
Kekuleacute structure Cyclohexa- 135 triene
χ doublesingle bonds bet them
Benzene
Hexagonal planar
Resonance Hybrid more stable than any of the resonance structure
Click here to view
Kekule
ResonanceDelocalization Energy
ΔH cyclohexene = -120kJmol-1
ΔH cyclohexa 13 diene = -240kJmol-1
ΔH cyclohexa 135 triene = -360kJmol-1
ΔH Benzene = -208kJmol-1
Enthalpy change hydrogenation
χ
helliphellip
bull Benzene lower in energy by 150kJbull More stable due to delocalization of π electrons
150kJ-150
3 Evidence for Benzene structure1
ResonanceDelocalization Energy
ΔH cyclohexene = -120kJmol-1
ΔH cyclohexa 13 diene = -240kJmol-1
ΔH cyclohexa 135 triene = -360kJmol-1
ΔH Benzene = -208kJmol-1
Enthalpy change hydrogenation
χ
helliphellip
bull Benzene lower in energy by 150kJbull More stable due to delocalization of π electrons
150kJ-150
C-CSingle bond
C=CDouble bond
C=CBenzene
Bond lengthpm 154 134 140
Bond enthalpykJmol-1
346 614 507
3 Evidence for Benzene structure1
2
bull X ray hit benzene crystalbull Interact with electron (electron density
map) bull X ray diffraction producedbull Bond length measured
X ray crystallography
NO singledouble bond detected
ResonanceDelocalization Energy
ΔH cyclohexene = -120kJmol-1
ΔH cyclohexa 13 diene = -240kJmol-1
ΔH cyclohexa 135 triene = -360kJmol-1
ΔH Benzene = -208kJmol-1
Enthalpy change hydrogenation
χ
helliphellip
bull Benzene lower in energy by 150kJbull More stable due to delocalization of π electrons
150kJ-150
C-CSingle bond
C=CDouble bond
C=CBenzene
Bond lengthpm 154 134 140
Bond enthalpykJmol-1
346 614 507
3 Evidence for Benzene structure1
2
Click here evidence against Kekule
bull X ray hit benzene crystalbull Interact with electron (electron density
map) bull X ray diffraction producedbull Bond length measured
X ray crystallography
NO singledouble bond detected
3 Addition reaction for unsaturated C=C
Addition reaction
Substitution reaction
NO double bond
Acknowledgements
Thanks to source of pictures and video used in this presentation
Thanks to Creative Commons for excellent contribution on licenseshttpspaceplacenasagovgreenhouseenhttpwwwozonedepletioninfoeducationpart3ozonesourceshtmlhttpcreativecommonsorglicenseshttpwwwciesinorgdocs011-462011-462htmlhttpwwwepmagazineorgstorage165benzene-evidenceaspx
Prepared by Lawrence Kok
Check out more video tutorials from my site and hope you enjoy this tutorialhttplawrencekokblogspotcom
Ozone absorb UV BC
How NO radical destroy ozone
Catalytic destruction of ozone
Ozone Depleting Substances (ODS)
Oxides of Nitrogen
Nitrogen Dioxide (NO2)
Nitrogen monoxide (nitric oxide NO)
Nitrous oxideN2O
Break down to form NO free radical (unpair electron)
+
Ozone absorb UV BC
NOx breaks down
How CFC breaks down
High UV BCHow NO radical destroy ozone
Catalytic destruction of ozone
Ozone Depleting Substances (ODS)
NO free radicals form
NO react O3 form NO2 radical
NO2 react O form NO radical again
Net eqn- ozone breaks down
Oxides of Nitrogen
Nitrogen Dioxide (NO2)
Nitrogen monoxide (nitric oxide NO)
Nitrous oxideN2O
Break down to form NO free radical (unpair electron)
NO NO2
NO2 NO + O2
+
Ozone absorb UV BC
NOx breaks down
How CFC breaks down
High UV BCHow NO radical destroy ozone
Catalytic destruction of ozone
Ozone Depleting Substances (ODS)
NO free radicals form
NO react O3 form NO2 radical
NO2 react O form NO radical again
Net eqn- ozone breaks down
Oxides of Nitrogen
Nitrogen Dioxide (NO2)
Nitrogen monoxide (nitric oxide NO)
Nitrous oxideN2O
Break down to form NO free radical (unpair electron)
NO NO2
NO2 NO + O2
Sources of NOx
Catalytic destruction of ozone
Ozone Depleting Substances (ODS)
Source of ODSbullHalogenated substancebullMan-made halocarbon refrigerant solvent propellantbullFoam-blowing agent (CFCs HCFCs freons halons)
Trichloroflouromethane CFC-11
Dichlorodifluoromethane CFC-12
Chlorodifluoromethane HCFC-22
Catalytic destruction of ozone
Ozone Depleting Substances (ODS)
Source of ODSbullHalogenated substancebullMan-made halocarbon refrigerant solvent propellantbullFoam-blowing agent (CFCs HCFCs freons halons)
CFCbullContain chlorine fluorine and carbon atomsbullExtremely stable with strong bonds long half lifebullStability allows CFC into the stratosphere bullHigh UV radiation reacts with CFCbullHigh UV photons breaks CFC (photochemical decomposition) bull Free Cl radicals form - destroying ozone
Trichloroflouromethane CFC-11
Dichlorodifluoromethane CFC-12
Chlorodifluoromethane HCFC-22
Why halogenate
d CFC used
Less harmful
Very harmful
Catalytic destruction of ozone
Ozone Depleting Substances (ODS)
Source of ODSbullHalogenated substancebullMan-made halocarbon refrigerant solvent propellantbullFoam-blowing agent (CFCs HCFCs freons halons)
Montreal Protocol bans CFC halon and ODS like carbon tetrachloride and trichloroethane
CFCbullContain chlorine fluorine and carbon atomsbullExtremely stable with strong bonds long half lifebullStability allows CFC into the stratosphere bullHigh UV radiation reacts with CFCbullHigh UV photons breaks CFC (photochemical decomposition) bull Free Cl radicals form - destroying ozone
Trichloroflouromethane CFC-11
Dichlorodifluoromethane CFC-12
Chlorodifluoromethane HCFC-22
Why halogenate
d CFC used
Less harmful
Very harmful
Why fluorinated is safer
Delocalization of electrons
Resonance bull Describing delocalization of electrons within a moleculepolyatomic ion where bonding cannot be express by ONE single Lewis structurebullDelocalization of π bond ndash π electrons spread over more than 2 nucleibullπ electrons are sharedbullπ electrons spread ndash more stable
Resonance structures benzene
Benzene6HC6
resonance structure 1 resonance structure 2
bull Unhybridised p orbitalbull Delocalization electrons above below planebull sp2 hybridization on carbon center
Delocalized electrons
Kekuleacute structure Cyclohexa- 135 triene
χ doublesingle bonds bet them
Benzene
Hexagonal planar
Kekule
Delocalization of electrons
Resonance bull Describing delocalization of electrons within a moleculepolyatomic ion where bonding cannot be express by ONE single Lewis structurebullDelocalization of π bond ndash π electrons spread over more than 2 nucleibullπ electrons are sharedbullπ electrons spread ndash more stable
Resonance structures benzene
Benzene6HC6
resonance structure 1 resonance structure 2
Resonance hybrid
bull All bonds C6H6 are identical in length strengthbull Hybrid of 2 resonance structuresbull No C-C (single) or C=C (double) bonds foundbull Only C ----- C bondbull Intermediate character bet singledouble bond
bull Bond Order =
bull Unhybridised p orbitalbull Delocalization electrons above below planebull sp2 hybridization on carbon center
15
Click here to view
Delocalized electrons
Kekuleacute structure Cyclohexa- 135 triene
χ doublesingle bonds bet them
Benzene
Hexagonal planar
Resonance Hybrid more stable than any of the resonance structure
Click here to view
Kekule
ResonanceDelocalization Energy
ΔH cyclohexene = -120kJmol-1
ΔH cyclohexa 13 diene = -240kJmol-1
ΔH cyclohexa 135 triene = -360kJmol-1
ΔH Benzene = -208kJmol-1
Enthalpy change hydrogenation
χ
helliphellip
bull Benzene lower in energy by 150kJbull More stable due to delocalization of π electrons
150kJ-150
3 Evidence for Benzene structure1
ResonanceDelocalization Energy
ΔH cyclohexene = -120kJmol-1
ΔH cyclohexa 13 diene = -240kJmol-1
ΔH cyclohexa 135 triene = -360kJmol-1
ΔH Benzene = -208kJmol-1
Enthalpy change hydrogenation
χ
helliphellip
bull Benzene lower in energy by 150kJbull More stable due to delocalization of π electrons
150kJ-150
C-CSingle bond
C=CDouble bond
C=CBenzene
Bond lengthpm 154 134 140
Bond enthalpykJmol-1
346 614 507
3 Evidence for Benzene structure1
2
bull X ray hit benzene crystalbull Interact with electron (electron density
map) bull X ray diffraction producedbull Bond length measured
X ray crystallography
NO singledouble bond detected
ResonanceDelocalization Energy
ΔH cyclohexene = -120kJmol-1
ΔH cyclohexa 13 diene = -240kJmol-1
ΔH cyclohexa 135 triene = -360kJmol-1
ΔH Benzene = -208kJmol-1
Enthalpy change hydrogenation
χ
helliphellip
bull Benzene lower in energy by 150kJbull More stable due to delocalization of π electrons
150kJ-150
C-CSingle bond
C=CDouble bond
C=CBenzene
Bond lengthpm 154 134 140
Bond enthalpykJmol-1
346 614 507
3 Evidence for Benzene structure1
2
Click here evidence against Kekule
bull X ray hit benzene crystalbull Interact with electron (electron density
map) bull X ray diffraction producedbull Bond length measured
X ray crystallography
NO singledouble bond detected
3 Addition reaction for unsaturated C=C
Addition reaction
Substitution reaction
NO double bond
Acknowledgements
Thanks to source of pictures and video used in this presentation
Thanks to Creative Commons for excellent contribution on licenseshttpspaceplacenasagovgreenhouseenhttpwwwozonedepletioninfoeducationpart3ozonesourceshtmlhttpcreativecommonsorglicenseshttpwwwciesinorgdocs011-462011-462htmlhttpwwwepmagazineorgstorage165benzene-evidenceaspx
Prepared by Lawrence Kok
Check out more video tutorials from my site and hope you enjoy this tutorialhttplawrencekokblogspotcom
+
Ozone absorb UV BC
NOx breaks down
How CFC breaks down
High UV BCHow NO radical destroy ozone
Catalytic destruction of ozone
Ozone Depleting Substances (ODS)
NO free radicals form
NO react O3 form NO2 radical
NO2 react O form NO radical again
Net eqn- ozone breaks down
Oxides of Nitrogen
Nitrogen Dioxide (NO2)
Nitrogen monoxide (nitric oxide NO)
Nitrous oxideN2O
Break down to form NO free radical (unpair electron)
NO NO2
NO2 NO + O2
+
Ozone absorb UV BC
NOx breaks down
How CFC breaks down
High UV BCHow NO radical destroy ozone
Catalytic destruction of ozone
Ozone Depleting Substances (ODS)
NO free radicals form
NO react O3 form NO2 radical
NO2 react O form NO radical again
Net eqn- ozone breaks down
Oxides of Nitrogen
Nitrogen Dioxide (NO2)
Nitrogen monoxide (nitric oxide NO)
Nitrous oxideN2O
Break down to form NO free radical (unpair electron)
NO NO2
NO2 NO + O2
Sources of NOx
Catalytic destruction of ozone
Ozone Depleting Substances (ODS)
Source of ODSbullHalogenated substancebullMan-made halocarbon refrigerant solvent propellantbullFoam-blowing agent (CFCs HCFCs freons halons)
Trichloroflouromethane CFC-11
Dichlorodifluoromethane CFC-12
Chlorodifluoromethane HCFC-22
Catalytic destruction of ozone
Ozone Depleting Substances (ODS)
Source of ODSbullHalogenated substancebullMan-made halocarbon refrigerant solvent propellantbullFoam-blowing agent (CFCs HCFCs freons halons)
CFCbullContain chlorine fluorine and carbon atomsbullExtremely stable with strong bonds long half lifebullStability allows CFC into the stratosphere bullHigh UV radiation reacts with CFCbullHigh UV photons breaks CFC (photochemical decomposition) bull Free Cl radicals form - destroying ozone
Trichloroflouromethane CFC-11
Dichlorodifluoromethane CFC-12
Chlorodifluoromethane HCFC-22
Why halogenate
d CFC used
Less harmful
Very harmful
Catalytic destruction of ozone
Ozone Depleting Substances (ODS)
Source of ODSbullHalogenated substancebullMan-made halocarbon refrigerant solvent propellantbullFoam-blowing agent (CFCs HCFCs freons halons)
Montreal Protocol bans CFC halon and ODS like carbon tetrachloride and trichloroethane
CFCbullContain chlorine fluorine and carbon atomsbullExtremely stable with strong bonds long half lifebullStability allows CFC into the stratosphere bullHigh UV radiation reacts with CFCbullHigh UV photons breaks CFC (photochemical decomposition) bull Free Cl radicals form - destroying ozone
Trichloroflouromethane CFC-11
Dichlorodifluoromethane CFC-12
Chlorodifluoromethane HCFC-22
Why halogenate
d CFC used
Less harmful
Very harmful
Why fluorinated is safer
Delocalization of electrons
Resonance bull Describing delocalization of electrons within a moleculepolyatomic ion where bonding cannot be express by ONE single Lewis structurebullDelocalization of π bond ndash π electrons spread over more than 2 nucleibullπ electrons are sharedbullπ electrons spread ndash more stable
Resonance structures benzene
Benzene6HC6
resonance structure 1 resonance structure 2
bull Unhybridised p orbitalbull Delocalization electrons above below planebull sp2 hybridization on carbon center
Delocalized electrons
Kekuleacute structure Cyclohexa- 135 triene
χ doublesingle bonds bet them
Benzene
Hexagonal planar
Kekule
Delocalization of electrons
Resonance bull Describing delocalization of electrons within a moleculepolyatomic ion where bonding cannot be express by ONE single Lewis structurebullDelocalization of π bond ndash π electrons spread over more than 2 nucleibullπ electrons are sharedbullπ electrons spread ndash more stable
Resonance structures benzene
Benzene6HC6
resonance structure 1 resonance structure 2
Resonance hybrid
bull All bonds C6H6 are identical in length strengthbull Hybrid of 2 resonance structuresbull No C-C (single) or C=C (double) bonds foundbull Only C ----- C bondbull Intermediate character bet singledouble bond
bull Bond Order =
bull Unhybridised p orbitalbull Delocalization electrons above below planebull sp2 hybridization on carbon center
15
Click here to view
Delocalized electrons
Kekuleacute structure Cyclohexa- 135 triene
χ doublesingle bonds bet them
Benzene
Hexagonal planar
Resonance Hybrid more stable than any of the resonance structure
Click here to view
Kekule
ResonanceDelocalization Energy
ΔH cyclohexene = -120kJmol-1
ΔH cyclohexa 13 diene = -240kJmol-1
ΔH cyclohexa 135 triene = -360kJmol-1
ΔH Benzene = -208kJmol-1
Enthalpy change hydrogenation
χ
helliphellip
bull Benzene lower in energy by 150kJbull More stable due to delocalization of π electrons
150kJ-150
3 Evidence for Benzene structure1
ResonanceDelocalization Energy
ΔH cyclohexene = -120kJmol-1
ΔH cyclohexa 13 diene = -240kJmol-1
ΔH cyclohexa 135 triene = -360kJmol-1
ΔH Benzene = -208kJmol-1
Enthalpy change hydrogenation
χ
helliphellip
bull Benzene lower in energy by 150kJbull More stable due to delocalization of π electrons
150kJ-150
C-CSingle bond
C=CDouble bond
C=CBenzene
Bond lengthpm 154 134 140
Bond enthalpykJmol-1
346 614 507
3 Evidence for Benzene structure1
2
bull X ray hit benzene crystalbull Interact with electron (electron density
map) bull X ray diffraction producedbull Bond length measured
X ray crystallography
NO singledouble bond detected
ResonanceDelocalization Energy
ΔH cyclohexene = -120kJmol-1
ΔH cyclohexa 13 diene = -240kJmol-1
ΔH cyclohexa 135 triene = -360kJmol-1
ΔH Benzene = -208kJmol-1
Enthalpy change hydrogenation
χ
helliphellip
bull Benzene lower in energy by 150kJbull More stable due to delocalization of π electrons
150kJ-150
C-CSingle bond
C=CDouble bond
C=CBenzene
Bond lengthpm 154 134 140
Bond enthalpykJmol-1
346 614 507
3 Evidence for Benzene structure1
2
Click here evidence against Kekule
bull X ray hit benzene crystalbull Interact with electron (electron density
map) bull X ray diffraction producedbull Bond length measured
X ray crystallography
NO singledouble bond detected
3 Addition reaction for unsaturated C=C
Addition reaction
Substitution reaction
NO double bond
Acknowledgements
Thanks to source of pictures and video used in this presentation
Thanks to Creative Commons for excellent contribution on licenseshttpspaceplacenasagovgreenhouseenhttpwwwozonedepletioninfoeducationpart3ozonesourceshtmlhttpcreativecommonsorglicenseshttpwwwciesinorgdocs011-462011-462htmlhttpwwwepmagazineorgstorage165benzene-evidenceaspx
Prepared by Lawrence Kok
Check out more video tutorials from my site and hope you enjoy this tutorialhttplawrencekokblogspotcom
+
Ozone absorb UV BC
NOx breaks down
How CFC breaks down
High UV BCHow NO radical destroy ozone
Catalytic destruction of ozone
Ozone Depleting Substances (ODS)
NO free radicals form
NO react O3 form NO2 radical
NO2 react O form NO radical again
Net eqn- ozone breaks down
Oxides of Nitrogen
Nitrogen Dioxide (NO2)
Nitrogen monoxide (nitric oxide NO)
Nitrous oxideN2O
Break down to form NO free radical (unpair electron)
NO NO2
NO2 NO + O2
Sources of NOx
Catalytic destruction of ozone
Ozone Depleting Substances (ODS)
Source of ODSbullHalogenated substancebullMan-made halocarbon refrigerant solvent propellantbullFoam-blowing agent (CFCs HCFCs freons halons)
Trichloroflouromethane CFC-11
Dichlorodifluoromethane CFC-12
Chlorodifluoromethane HCFC-22
Catalytic destruction of ozone
Ozone Depleting Substances (ODS)
Source of ODSbullHalogenated substancebullMan-made halocarbon refrigerant solvent propellantbullFoam-blowing agent (CFCs HCFCs freons halons)
CFCbullContain chlorine fluorine and carbon atomsbullExtremely stable with strong bonds long half lifebullStability allows CFC into the stratosphere bullHigh UV radiation reacts with CFCbullHigh UV photons breaks CFC (photochemical decomposition) bull Free Cl radicals form - destroying ozone
Trichloroflouromethane CFC-11
Dichlorodifluoromethane CFC-12
Chlorodifluoromethane HCFC-22
Why halogenate
d CFC used
Less harmful
Very harmful
Catalytic destruction of ozone
Ozone Depleting Substances (ODS)
Source of ODSbullHalogenated substancebullMan-made halocarbon refrigerant solvent propellantbullFoam-blowing agent (CFCs HCFCs freons halons)
Montreal Protocol bans CFC halon and ODS like carbon tetrachloride and trichloroethane
CFCbullContain chlorine fluorine and carbon atomsbullExtremely stable with strong bonds long half lifebullStability allows CFC into the stratosphere bullHigh UV radiation reacts with CFCbullHigh UV photons breaks CFC (photochemical decomposition) bull Free Cl radicals form - destroying ozone
Trichloroflouromethane CFC-11
Dichlorodifluoromethane CFC-12
Chlorodifluoromethane HCFC-22
Why halogenate
d CFC used
Less harmful
Very harmful
Why fluorinated is safer
Delocalization of electrons
Resonance bull Describing delocalization of electrons within a moleculepolyatomic ion where bonding cannot be express by ONE single Lewis structurebullDelocalization of π bond ndash π electrons spread over more than 2 nucleibullπ electrons are sharedbullπ electrons spread ndash more stable
Resonance structures benzene
Benzene6HC6
resonance structure 1 resonance structure 2
bull Unhybridised p orbitalbull Delocalization electrons above below planebull sp2 hybridization on carbon center
Delocalized electrons
Kekuleacute structure Cyclohexa- 135 triene
χ doublesingle bonds bet them
Benzene
Hexagonal planar
Kekule
Delocalization of electrons
Resonance bull Describing delocalization of electrons within a moleculepolyatomic ion where bonding cannot be express by ONE single Lewis structurebullDelocalization of π bond ndash π electrons spread over more than 2 nucleibullπ electrons are sharedbullπ electrons spread ndash more stable
Resonance structures benzene
Benzene6HC6
resonance structure 1 resonance structure 2
Resonance hybrid
bull All bonds C6H6 are identical in length strengthbull Hybrid of 2 resonance structuresbull No C-C (single) or C=C (double) bonds foundbull Only C ----- C bondbull Intermediate character bet singledouble bond
bull Bond Order =
bull Unhybridised p orbitalbull Delocalization electrons above below planebull sp2 hybridization on carbon center
15
Click here to view
Delocalized electrons
Kekuleacute structure Cyclohexa- 135 triene
χ doublesingle bonds bet them
Benzene
Hexagonal planar
Resonance Hybrid more stable than any of the resonance structure
Click here to view
Kekule
ResonanceDelocalization Energy
ΔH cyclohexene = -120kJmol-1
ΔH cyclohexa 13 diene = -240kJmol-1
ΔH cyclohexa 135 triene = -360kJmol-1
ΔH Benzene = -208kJmol-1
Enthalpy change hydrogenation
χ
helliphellip
bull Benzene lower in energy by 150kJbull More stable due to delocalization of π electrons
150kJ-150
3 Evidence for Benzene structure1
ResonanceDelocalization Energy
ΔH cyclohexene = -120kJmol-1
ΔH cyclohexa 13 diene = -240kJmol-1
ΔH cyclohexa 135 triene = -360kJmol-1
ΔH Benzene = -208kJmol-1
Enthalpy change hydrogenation
χ
helliphellip
bull Benzene lower in energy by 150kJbull More stable due to delocalization of π electrons
150kJ-150
C-CSingle bond
C=CDouble bond
C=CBenzene
Bond lengthpm 154 134 140
Bond enthalpykJmol-1
346 614 507
3 Evidence for Benzene structure1
2
bull X ray hit benzene crystalbull Interact with electron (electron density
map) bull X ray diffraction producedbull Bond length measured
X ray crystallography
NO singledouble bond detected
ResonanceDelocalization Energy
ΔH cyclohexene = -120kJmol-1
ΔH cyclohexa 13 diene = -240kJmol-1
ΔH cyclohexa 135 triene = -360kJmol-1
ΔH Benzene = -208kJmol-1
Enthalpy change hydrogenation
χ
helliphellip
bull Benzene lower in energy by 150kJbull More stable due to delocalization of π electrons
150kJ-150
C-CSingle bond
C=CDouble bond
C=CBenzene
Bond lengthpm 154 134 140
Bond enthalpykJmol-1
346 614 507
3 Evidence for Benzene structure1
2
Click here evidence against Kekule
bull X ray hit benzene crystalbull Interact with electron (electron density
map) bull X ray diffraction producedbull Bond length measured
X ray crystallography
NO singledouble bond detected
3 Addition reaction for unsaturated C=C
Addition reaction
Substitution reaction
NO double bond
Acknowledgements
Thanks to source of pictures and video used in this presentation
Thanks to Creative Commons for excellent contribution on licenseshttpspaceplacenasagovgreenhouseenhttpwwwozonedepletioninfoeducationpart3ozonesourceshtmlhttpcreativecommonsorglicenseshttpwwwciesinorgdocs011-462011-462htmlhttpwwwepmagazineorgstorage165benzene-evidenceaspx
Prepared by Lawrence Kok
Check out more video tutorials from my site and hope you enjoy this tutorialhttplawrencekokblogspotcom
Catalytic destruction of ozone
Ozone Depleting Substances (ODS)
Source of ODSbullHalogenated substancebullMan-made halocarbon refrigerant solvent propellantbullFoam-blowing agent (CFCs HCFCs freons halons)
Trichloroflouromethane CFC-11
Dichlorodifluoromethane CFC-12
Chlorodifluoromethane HCFC-22
Catalytic destruction of ozone
Ozone Depleting Substances (ODS)
Source of ODSbullHalogenated substancebullMan-made halocarbon refrigerant solvent propellantbullFoam-blowing agent (CFCs HCFCs freons halons)
CFCbullContain chlorine fluorine and carbon atomsbullExtremely stable with strong bonds long half lifebullStability allows CFC into the stratosphere bullHigh UV radiation reacts with CFCbullHigh UV photons breaks CFC (photochemical decomposition) bull Free Cl radicals form - destroying ozone
Trichloroflouromethane CFC-11
Dichlorodifluoromethane CFC-12
Chlorodifluoromethane HCFC-22
Why halogenate
d CFC used
Less harmful
Very harmful
Catalytic destruction of ozone
Ozone Depleting Substances (ODS)
Source of ODSbullHalogenated substancebullMan-made halocarbon refrigerant solvent propellantbullFoam-blowing agent (CFCs HCFCs freons halons)
Montreal Protocol bans CFC halon and ODS like carbon tetrachloride and trichloroethane
CFCbullContain chlorine fluorine and carbon atomsbullExtremely stable with strong bonds long half lifebullStability allows CFC into the stratosphere bullHigh UV radiation reacts with CFCbullHigh UV photons breaks CFC (photochemical decomposition) bull Free Cl radicals form - destroying ozone
Trichloroflouromethane CFC-11
Dichlorodifluoromethane CFC-12
Chlorodifluoromethane HCFC-22
Why halogenate
d CFC used
Less harmful
Very harmful
Why fluorinated is safer
Delocalization of electrons
Resonance bull Describing delocalization of electrons within a moleculepolyatomic ion where bonding cannot be express by ONE single Lewis structurebullDelocalization of π bond ndash π electrons spread over more than 2 nucleibullπ electrons are sharedbullπ electrons spread ndash more stable
Resonance structures benzene
Benzene6HC6
resonance structure 1 resonance structure 2
bull Unhybridised p orbitalbull Delocalization electrons above below planebull sp2 hybridization on carbon center
Delocalized electrons
Kekuleacute structure Cyclohexa- 135 triene
χ doublesingle bonds bet them
Benzene
Hexagonal planar
Kekule
Delocalization of electrons
Resonance bull Describing delocalization of electrons within a moleculepolyatomic ion where bonding cannot be express by ONE single Lewis structurebullDelocalization of π bond ndash π electrons spread over more than 2 nucleibullπ electrons are sharedbullπ electrons spread ndash more stable
Resonance structures benzene
Benzene6HC6
resonance structure 1 resonance structure 2
Resonance hybrid
bull All bonds C6H6 are identical in length strengthbull Hybrid of 2 resonance structuresbull No C-C (single) or C=C (double) bonds foundbull Only C ----- C bondbull Intermediate character bet singledouble bond
bull Bond Order =
bull Unhybridised p orbitalbull Delocalization electrons above below planebull sp2 hybridization on carbon center
15
Click here to view
Delocalized electrons
Kekuleacute structure Cyclohexa- 135 triene
χ doublesingle bonds bet them
Benzene
Hexagonal planar
Resonance Hybrid more stable than any of the resonance structure
Click here to view
Kekule
ResonanceDelocalization Energy
ΔH cyclohexene = -120kJmol-1
ΔH cyclohexa 13 diene = -240kJmol-1
ΔH cyclohexa 135 triene = -360kJmol-1
ΔH Benzene = -208kJmol-1
Enthalpy change hydrogenation
χ
helliphellip
bull Benzene lower in energy by 150kJbull More stable due to delocalization of π electrons
150kJ-150
3 Evidence for Benzene structure1
ResonanceDelocalization Energy
ΔH cyclohexene = -120kJmol-1
ΔH cyclohexa 13 diene = -240kJmol-1
ΔH cyclohexa 135 triene = -360kJmol-1
ΔH Benzene = -208kJmol-1
Enthalpy change hydrogenation
χ
helliphellip
bull Benzene lower in energy by 150kJbull More stable due to delocalization of π electrons
150kJ-150
C-CSingle bond
C=CDouble bond
C=CBenzene
Bond lengthpm 154 134 140
Bond enthalpykJmol-1
346 614 507
3 Evidence for Benzene structure1
2
bull X ray hit benzene crystalbull Interact with electron (electron density
map) bull X ray diffraction producedbull Bond length measured
X ray crystallography
NO singledouble bond detected
ResonanceDelocalization Energy
ΔH cyclohexene = -120kJmol-1
ΔH cyclohexa 13 diene = -240kJmol-1
ΔH cyclohexa 135 triene = -360kJmol-1
ΔH Benzene = -208kJmol-1
Enthalpy change hydrogenation
χ
helliphellip
bull Benzene lower in energy by 150kJbull More stable due to delocalization of π electrons
150kJ-150
C-CSingle bond
C=CDouble bond
C=CBenzene
Bond lengthpm 154 134 140
Bond enthalpykJmol-1
346 614 507
3 Evidence for Benzene structure1
2
Click here evidence against Kekule
bull X ray hit benzene crystalbull Interact with electron (electron density
map) bull X ray diffraction producedbull Bond length measured
X ray crystallography
NO singledouble bond detected
3 Addition reaction for unsaturated C=C
Addition reaction
Substitution reaction
NO double bond
Acknowledgements
Thanks to source of pictures and video used in this presentation
Thanks to Creative Commons for excellent contribution on licenseshttpspaceplacenasagovgreenhouseenhttpwwwozonedepletioninfoeducationpart3ozonesourceshtmlhttpcreativecommonsorglicenseshttpwwwciesinorgdocs011-462011-462htmlhttpwwwepmagazineorgstorage165benzene-evidenceaspx
Prepared by Lawrence Kok
Check out more video tutorials from my site and hope you enjoy this tutorialhttplawrencekokblogspotcom
Catalytic destruction of ozone
Ozone Depleting Substances (ODS)
Source of ODSbullHalogenated substancebullMan-made halocarbon refrigerant solvent propellantbullFoam-blowing agent (CFCs HCFCs freons halons)
CFCbullContain chlorine fluorine and carbon atomsbullExtremely stable with strong bonds long half lifebullStability allows CFC into the stratosphere bullHigh UV radiation reacts with CFCbullHigh UV photons breaks CFC (photochemical decomposition) bull Free Cl radicals form - destroying ozone
Trichloroflouromethane CFC-11
Dichlorodifluoromethane CFC-12
Chlorodifluoromethane HCFC-22
Why halogenate
d CFC used
Less harmful
Very harmful
Catalytic destruction of ozone
Ozone Depleting Substances (ODS)
Source of ODSbullHalogenated substancebullMan-made halocarbon refrigerant solvent propellantbullFoam-blowing agent (CFCs HCFCs freons halons)
Montreal Protocol bans CFC halon and ODS like carbon tetrachloride and trichloroethane
CFCbullContain chlorine fluorine and carbon atomsbullExtremely stable with strong bonds long half lifebullStability allows CFC into the stratosphere bullHigh UV radiation reacts with CFCbullHigh UV photons breaks CFC (photochemical decomposition) bull Free Cl radicals form - destroying ozone
Trichloroflouromethane CFC-11
Dichlorodifluoromethane CFC-12
Chlorodifluoromethane HCFC-22
Why halogenate
d CFC used
Less harmful
Very harmful
Why fluorinated is safer
Delocalization of electrons
Resonance bull Describing delocalization of electrons within a moleculepolyatomic ion where bonding cannot be express by ONE single Lewis structurebullDelocalization of π bond ndash π electrons spread over more than 2 nucleibullπ electrons are sharedbullπ electrons spread ndash more stable
Resonance structures benzene
Benzene6HC6
resonance structure 1 resonance structure 2
bull Unhybridised p orbitalbull Delocalization electrons above below planebull sp2 hybridization on carbon center
Delocalized electrons
Kekuleacute structure Cyclohexa- 135 triene
χ doublesingle bonds bet them
Benzene
Hexagonal planar
Kekule
Delocalization of electrons
Resonance bull Describing delocalization of electrons within a moleculepolyatomic ion where bonding cannot be express by ONE single Lewis structurebullDelocalization of π bond ndash π electrons spread over more than 2 nucleibullπ electrons are sharedbullπ electrons spread ndash more stable
Resonance structures benzene
Benzene6HC6
resonance structure 1 resonance structure 2
Resonance hybrid
bull All bonds C6H6 are identical in length strengthbull Hybrid of 2 resonance structuresbull No C-C (single) or C=C (double) bonds foundbull Only C ----- C bondbull Intermediate character bet singledouble bond
bull Bond Order =
bull Unhybridised p orbitalbull Delocalization electrons above below planebull sp2 hybridization on carbon center
15
Click here to view
Delocalized electrons
Kekuleacute structure Cyclohexa- 135 triene
χ doublesingle bonds bet them
Benzene
Hexagonal planar
Resonance Hybrid more stable than any of the resonance structure
Click here to view
Kekule
ResonanceDelocalization Energy
ΔH cyclohexene = -120kJmol-1
ΔH cyclohexa 13 diene = -240kJmol-1
ΔH cyclohexa 135 triene = -360kJmol-1
ΔH Benzene = -208kJmol-1
Enthalpy change hydrogenation
χ
helliphellip
bull Benzene lower in energy by 150kJbull More stable due to delocalization of π electrons
150kJ-150
3 Evidence for Benzene structure1
ResonanceDelocalization Energy
ΔH cyclohexene = -120kJmol-1
ΔH cyclohexa 13 diene = -240kJmol-1
ΔH cyclohexa 135 triene = -360kJmol-1
ΔH Benzene = -208kJmol-1
Enthalpy change hydrogenation
χ
helliphellip
bull Benzene lower in energy by 150kJbull More stable due to delocalization of π electrons
150kJ-150
C-CSingle bond
C=CDouble bond
C=CBenzene
Bond lengthpm 154 134 140
Bond enthalpykJmol-1
346 614 507
3 Evidence for Benzene structure1
2
bull X ray hit benzene crystalbull Interact with electron (electron density
map) bull X ray diffraction producedbull Bond length measured
X ray crystallography
NO singledouble bond detected
ResonanceDelocalization Energy
ΔH cyclohexene = -120kJmol-1
ΔH cyclohexa 13 diene = -240kJmol-1
ΔH cyclohexa 135 triene = -360kJmol-1
ΔH Benzene = -208kJmol-1
Enthalpy change hydrogenation
χ
helliphellip
bull Benzene lower in energy by 150kJbull More stable due to delocalization of π electrons
150kJ-150
C-CSingle bond
C=CDouble bond
C=CBenzene
Bond lengthpm 154 134 140
Bond enthalpykJmol-1
346 614 507
3 Evidence for Benzene structure1
2
Click here evidence against Kekule
bull X ray hit benzene crystalbull Interact with electron (electron density
map) bull X ray diffraction producedbull Bond length measured
X ray crystallography
NO singledouble bond detected
3 Addition reaction for unsaturated C=C
Addition reaction
Substitution reaction
NO double bond
Acknowledgements
Thanks to source of pictures and video used in this presentation
Thanks to Creative Commons for excellent contribution on licenseshttpspaceplacenasagovgreenhouseenhttpwwwozonedepletioninfoeducationpart3ozonesourceshtmlhttpcreativecommonsorglicenseshttpwwwciesinorgdocs011-462011-462htmlhttpwwwepmagazineorgstorage165benzene-evidenceaspx
Prepared by Lawrence Kok
Check out more video tutorials from my site and hope you enjoy this tutorialhttplawrencekokblogspotcom
Catalytic destruction of ozone
Ozone Depleting Substances (ODS)
Source of ODSbullHalogenated substancebullMan-made halocarbon refrigerant solvent propellantbullFoam-blowing agent (CFCs HCFCs freons halons)
Montreal Protocol bans CFC halon and ODS like carbon tetrachloride and trichloroethane
CFCbullContain chlorine fluorine and carbon atomsbullExtremely stable with strong bonds long half lifebullStability allows CFC into the stratosphere bullHigh UV radiation reacts with CFCbullHigh UV photons breaks CFC (photochemical decomposition) bull Free Cl radicals form - destroying ozone
Trichloroflouromethane CFC-11
Dichlorodifluoromethane CFC-12
Chlorodifluoromethane HCFC-22
Why halogenate
d CFC used
Less harmful
Very harmful
Why fluorinated is safer
Delocalization of electrons
Resonance bull Describing delocalization of electrons within a moleculepolyatomic ion where bonding cannot be express by ONE single Lewis structurebullDelocalization of π bond ndash π electrons spread over more than 2 nucleibullπ electrons are sharedbullπ electrons spread ndash more stable
Resonance structures benzene
Benzene6HC6
resonance structure 1 resonance structure 2
bull Unhybridised p orbitalbull Delocalization electrons above below planebull sp2 hybridization on carbon center
Delocalized electrons
Kekuleacute structure Cyclohexa- 135 triene
χ doublesingle bonds bet them
Benzene
Hexagonal planar
Kekule
Delocalization of electrons
Resonance bull Describing delocalization of electrons within a moleculepolyatomic ion where bonding cannot be express by ONE single Lewis structurebullDelocalization of π bond ndash π electrons spread over more than 2 nucleibullπ electrons are sharedbullπ electrons spread ndash more stable
Resonance structures benzene
Benzene6HC6
resonance structure 1 resonance structure 2
Resonance hybrid
bull All bonds C6H6 are identical in length strengthbull Hybrid of 2 resonance structuresbull No C-C (single) or C=C (double) bonds foundbull Only C ----- C bondbull Intermediate character bet singledouble bond
bull Bond Order =
bull Unhybridised p orbitalbull Delocalization electrons above below planebull sp2 hybridization on carbon center
15
Click here to view
Delocalized electrons
Kekuleacute structure Cyclohexa- 135 triene
χ doublesingle bonds bet them
Benzene
Hexagonal planar
Resonance Hybrid more stable than any of the resonance structure
Click here to view
Kekule
ResonanceDelocalization Energy
ΔH cyclohexene = -120kJmol-1
ΔH cyclohexa 13 diene = -240kJmol-1
ΔH cyclohexa 135 triene = -360kJmol-1
ΔH Benzene = -208kJmol-1
Enthalpy change hydrogenation
χ
helliphellip
bull Benzene lower in energy by 150kJbull More stable due to delocalization of π electrons
150kJ-150
3 Evidence for Benzene structure1
ResonanceDelocalization Energy
ΔH cyclohexene = -120kJmol-1
ΔH cyclohexa 13 diene = -240kJmol-1
ΔH cyclohexa 135 triene = -360kJmol-1
ΔH Benzene = -208kJmol-1
Enthalpy change hydrogenation
χ
helliphellip
bull Benzene lower in energy by 150kJbull More stable due to delocalization of π electrons
150kJ-150
C-CSingle bond
C=CDouble bond
C=CBenzene
Bond lengthpm 154 134 140
Bond enthalpykJmol-1
346 614 507
3 Evidence for Benzene structure1
2
bull X ray hit benzene crystalbull Interact with electron (electron density
map) bull X ray diffraction producedbull Bond length measured
X ray crystallography
NO singledouble bond detected
ResonanceDelocalization Energy
ΔH cyclohexene = -120kJmol-1
ΔH cyclohexa 13 diene = -240kJmol-1
ΔH cyclohexa 135 triene = -360kJmol-1
ΔH Benzene = -208kJmol-1
Enthalpy change hydrogenation
χ
helliphellip
bull Benzene lower in energy by 150kJbull More stable due to delocalization of π electrons
150kJ-150
C-CSingle bond
C=CDouble bond
C=CBenzene
Bond lengthpm 154 134 140
Bond enthalpykJmol-1
346 614 507
3 Evidence for Benzene structure1
2
Click here evidence against Kekule
bull X ray hit benzene crystalbull Interact with electron (electron density
map) bull X ray diffraction producedbull Bond length measured
X ray crystallography
NO singledouble bond detected
3 Addition reaction for unsaturated C=C
Addition reaction
Substitution reaction
NO double bond
Acknowledgements
Thanks to source of pictures and video used in this presentation
Thanks to Creative Commons for excellent contribution on licenseshttpspaceplacenasagovgreenhouseenhttpwwwozonedepletioninfoeducationpart3ozonesourceshtmlhttpcreativecommonsorglicenseshttpwwwciesinorgdocs011-462011-462htmlhttpwwwepmagazineorgstorage165benzene-evidenceaspx
Prepared by Lawrence Kok
Check out more video tutorials from my site and hope you enjoy this tutorialhttplawrencekokblogspotcom
Delocalization of electrons
Resonance bull Describing delocalization of electrons within a moleculepolyatomic ion where bonding cannot be express by ONE single Lewis structurebullDelocalization of π bond ndash π electrons spread over more than 2 nucleibullπ electrons are sharedbullπ electrons spread ndash more stable
Resonance structures benzene
Benzene6HC6
resonance structure 1 resonance structure 2
bull Unhybridised p orbitalbull Delocalization electrons above below planebull sp2 hybridization on carbon center
Delocalized electrons
Kekuleacute structure Cyclohexa- 135 triene
χ doublesingle bonds bet them
Benzene
Hexagonal planar
Kekule
Delocalization of electrons
Resonance bull Describing delocalization of electrons within a moleculepolyatomic ion where bonding cannot be express by ONE single Lewis structurebullDelocalization of π bond ndash π electrons spread over more than 2 nucleibullπ electrons are sharedbullπ electrons spread ndash more stable
Resonance structures benzene
Benzene6HC6
resonance structure 1 resonance structure 2
Resonance hybrid
bull All bonds C6H6 are identical in length strengthbull Hybrid of 2 resonance structuresbull No C-C (single) or C=C (double) bonds foundbull Only C ----- C bondbull Intermediate character bet singledouble bond
bull Bond Order =
bull Unhybridised p orbitalbull Delocalization electrons above below planebull sp2 hybridization on carbon center
15
Click here to view
Delocalized electrons
Kekuleacute structure Cyclohexa- 135 triene
χ doublesingle bonds bet them
Benzene
Hexagonal planar
Resonance Hybrid more stable than any of the resonance structure
Click here to view
Kekule
ResonanceDelocalization Energy
ΔH cyclohexene = -120kJmol-1
ΔH cyclohexa 13 diene = -240kJmol-1
ΔH cyclohexa 135 triene = -360kJmol-1
ΔH Benzene = -208kJmol-1
Enthalpy change hydrogenation
χ
helliphellip
bull Benzene lower in energy by 150kJbull More stable due to delocalization of π electrons
150kJ-150
3 Evidence for Benzene structure1
ResonanceDelocalization Energy
ΔH cyclohexene = -120kJmol-1
ΔH cyclohexa 13 diene = -240kJmol-1
ΔH cyclohexa 135 triene = -360kJmol-1
ΔH Benzene = -208kJmol-1
Enthalpy change hydrogenation
χ
helliphellip
bull Benzene lower in energy by 150kJbull More stable due to delocalization of π electrons
150kJ-150
C-CSingle bond
C=CDouble bond
C=CBenzene
Bond lengthpm 154 134 140
Bond enthalpykJmol-1
346 614 507
3 Evidence for Benzene structure1
2
bull X ray hit benzene crystalbull Interact with electron (electron density
map) bull X ray diffraction producedbull Bond length measured
X ray crystallography
NO singledouble bond detected
ResonanceDelocalization Energy
ΔH cyclohexene = -120kJmol-1
ΔH cyclohexa 13 diene = -240kJmol-1
ΔH cyclohexa 135 triene = -360kJmol-1
ΔH Benzene = -208kJmol-1
Enthalpy change hydrogenation
χ
helliphellip
bull Benzene lower in energy by 150kJbull More stable due to delocalization of π electrons
150kJ-150
C-CSingle bond
C=CDouble bond
C=CBenzene
Bond lengthpm 154 134 140
Bond enthalpykJmol-1
346 614 507
3 Evidence for Benzene structure1
2
Click here evidence against Kekule
bull X ray hit benzene crystalbull Interact with electron (electron density
map) bull X ray diffraction producedbull Bond length measured
X ray crystallography
NO singledouble bond detected
3 Addition reaction for unsaturated C=C
Addition reaction
Substitution reaction
NO double bond
Acknowledgements
Thanks to source of pictures and video used in this presentation
Thanks to Creative Commons for excellent contribution on licenseshttpspaceplacenasagovgreenhouseenhttpwwwozonedepletioninfoeducationpart3ozonesourceshtmlhttpcreativecommonsorglicenseshttpwwwciesinorgdocs011-462011-462htmlhttpwwwepmagazineorgstorage165benzene-evidenceaspx
Prepared by Lawrence Kok
Check out more video tutorials from my site and hope you enjoy this tutorialhttplawrencekokblogspotcom
Delocalization of electrons
Resonance bull Describing delocalization of electrons within a moleculepolyatomic ion where bonding cannot be express by ONE single Lewis structurebullDelocalization of π bond ndash π electrons spread over more than 2 nucleibullπ electrons are sharedbullπ electrons spread ndash more stable
Resonance structures benzene
Benzene6HC6
resonance structure 1 resonance structure 2
Resonance hybrid
bull All bonds C6H6 are identical in length strengthbull Hybrid of 2 resonance structuresbull No C-C (single) or C=C (double) bonds foundbull Only C ----- C bondbull Intermediate character bet singledouble bond
bull Bond Order =
bull Unhybridised p orbitalbull Delocalization electrons above below planebull sp2 hybridization on carbon center
15
Click here to view
Delocalized electrons
Kekuleacute structure Cyclohexa- 135 triene
χ doublesingle bonds bet them
Benzene
Hexagonal planar
Resonance Hybrid more stable than any of the resonance structure
Click here to view
Kekule
ResonanceDelocalization Energy
ΔH cyclohexene = -120kJmol-1
ΔH cyclohexa 13 diene = -240kJmol-1
ΔH cyclohexa 135 triene = -360kJmol-1
ΔH Benzene = -208kJmol-1
Enthalpy change hydrogenation
χ
helliphellip
bull Benzene lower in energy by 150kJbull More stable due to delocalization of π electrons
150kJ-150
3 Evidence for Benzene structure1
ResonanceDelocalization Energy
ΔH cyclohexene = -120kJmol-1
ΔH cyclohexa 13 diene = -240kJmol-1
ΔH cyclohexa 135 triene = -360kJmol-1
ΔH Benzene = -208kJmol-1
Enthalpy change hydrogenation
χ
helliphellip
bull Benzene lower in energy by 150kJbull More stable due to delocalization of π electrons
150kJ-150
C-CSingle bond
C=CDouble bond
C=CBenzene
Bond lengthpm 154 134 140
Bond enthalpykJmol-1
346 614 507
3 Evidence for Benzene structure1
2
bull X ray hit benzene crystalbull Interact with electron (electron density
map) bull X ray diffraction producedbull Bond length measured
X ray crystallography
NO singledouble bond detected
ResonanceDelocalization Energy
ΔH cyclohexene = -120kJmol-1
ΔH cyclohexa 13 diene = -240kJmol-1
ΔH cyclohexa 135 triene = -360kJmol-1
ΔH Benzene = -208kJmol-1
Enthalpy change hydrogenation
χ
helliphellip
bull Benzene lower in energy by 150kJbull More stable due to delocalization of π electrons
150kJ-150
C-CSingle bond
C=CDouble bond
C=CBenzene
Bond lengthpm 154 134 140
Bond enthalpykJmol-1
346 614 507
3 Evidence for Benzene structure1
2
Click here evidence against Kekule
bull X ray hit benzene crystalbull Interact with electron (electron density
map) bull X ray diffraction producedbull Bond length measured
X ray crystallography
NO singledouble bond detected
3 Addition reaction for unsaturated C=C
Addition reaction
Substitution reaction
NO double bond
Acknowledgements
Thanks to source of pictures and video used in this presentation
Thanks to Creative Commons for excellent contribution on licenseshttpspaceplacenasagovgreenhouseenhttpwwwozonedepletioninfoeducationpart3ozonesourceshtmlhttpcreativecommonsorglicenseshttpwwwciesinorgdocs011-462011-462htmlhttpwwwepmagazineorgstorage165benzene-evidenceaspx
Prepared by Lawrence Kok
Check out more video tutorials from my site and hope you enjoy this tutorialhttplawrencekokblogspotcom
ResonanceDelocalization Energy
ΔH cyclohexene = -120kJmol-1
ΔH cyclohexa 13 diene = -240kJmol-1
ΔH cyclohexa 135 triene = -360kJmol-1
ΔH Benzene = -208kJmol-1
Enthalpy change hydrogenation
χ
helliphellip
bull Benzene lower in energy by 150kJbull More stable due to delocalization of π electrons
150kJ-150
3 Evidence for Benzene structure1
ResonanceDelocalization Energy
ΔH cyclohexene = -120kJmol-1
ΔH cyclohexa 13 diene = -240kJmol-1
ΔH cyclohexa 135 triene = -360kJmol-1
ΔH Benzene = -208kJmol-1
Enthalpy change hydrogenation
χ
helliphellip
bull Benzene lower in energy by 150kJbull More stable due to delocalization of π electrons
150kJ-150
C-CSingle bond
C=CDouble bond
C=CBenzene
Bond lengthpm 154 134 140
Bond enthalpykJmol-1
346 614 507
3 Evidence for Benzene structure1
2
bull X ray hit benzene crystalbull Interact with electron (electron density
map) bull X ray diffraction producedbull Bond length measured
X ray crystallography
NO singledouble bond detected
ResonanceDelocalization Energy
ΔH cyclohexene = -120kJmol-1
ΔH cyclohexa 13 diene = -240kJmol-1
ΔH cyclohexa 135 triene = -360kJmol-1
ΔH Benzene = -208kJmol-1
Enthalpy change hydrogenation
χ
helliphellip
bull Benzene lower in energy by 150kJbull More stable due to delocalization of π electrons
150kJ-150
C-CSingle bond
C=CDouble bond
C=CBenzene
Bond lengthpm 154 134 140
Bond enthalpykJmol-1
346 614 507
3 Evidence for Benzene structure1
2
Click here evidence against Kekule
bull X ray hit benzene crystalbull Interact with electron (electron density
map) bull X ray diffraction producedbull Bond length measured
X ray crystallography
NO singledouble bond detected
3 Addition reaction for unsaturated C=C
Addition reaction
Substitution reaction
NO double bond
Acknowledgements
Thanks to source of pictures and video used in this presentation
Thanks to Creative Commons for excellent contribution on licenseshttpspaceplacenasagovgreenhouseenhttpwwwozonedepletioninfoeducationpart3ozonesourceshtmlhttpcreativecommonsorglicenseshttpwwwciesinorgdocs011-462011-462htmlhttpwwwepmagazineorgstorage165benzene-evidenceaspx
Prepared by Lawrence Kok
Check out more video tutorials from my site and hope you enjoy this tutorialhttplawrencekokblogspotcom
ResonanceDelocalization Energy
ΔH cyclohexene = -120kJmol-1
ΔH cyclohexa 13 diene = -240kJmol-1
ΔH cyclohexa 135 triene = -360kJmol-1
ΔH Benzene = -208kJmol-1
Enthalpy change hydrogenation
χ
helliphellip
bull Benzene lower in energy by 150kJbull More stable due to delocalization of π electrons
150kJ-150
C-CSingle bond
C=CDouble bond
C=CBenzene
Bond lengthpm 154 134 140
Bond enthalpykJmol-1
346 614 507
3 Evidence for Benzene structure1
2
bull X ray hit benzene crystalbull Interact with electron (electron density
map) bull X ray diffraction producedbull Bond length measured
X ray crystallography
NO singledouble bond detected
ResonanceDelocalization Energy
ΔH cyclohexene = -120kJmol-1
ΔH cyclohexa 13 diene = -240kJmol-1
ΔH cyclohexa 135 triene = -360kJmol-1
ΔH Benzene = -208kJmol-1
Enthalpy change hydrogenation
χ
helliphellip
bull Benzene lower in energy by 150kJbull More stable due to delocalization of π electrons
150kJ-150
C-CSingle bond
C=CDouble bond
C=CBenzene
Bond lengthpm 154 134 140
Bond enthalpykJmol-1
346 614 507
3 Evidence for Benzene structure1
2
Click here evidence against Kekule
bull X ray hit benzene crystalbull Interact with electron (electron density
map) bull X ray diffraction producedbull Bond length measured
X ray crystallography
NO singledouble bond detected
3 Addition reaction for unsaturated C=C
Addition reaction
Substitution reaction
NO double bond
Acknowledgements
Thanks to source of pictures and video used in this presentation
Thanks to Creative Commons for excellent contribution on licenseshttpspaceplacenasagovgreenhouseenhttpwwwozonedepletioninfoeducationpart3ozonesourceshtmlhttpcreativecommonsorglicenseshttpwwwciesinorgdocs011-462011-462htmlhttpwwwepmagazineorgstorage165benzene-evidenceaspx
Prepared by Lawrence Kok
Check out more video tutorials from my site and hope you enjoy this tutorialhttplawrencekokblogspotcom
ResonanceDelocalization Energy
ΔH cyclohexene = -120kJmol-1
ΔH cyclohexa 13 diene = -240kJmol-1
ΔH cyclohexa 135 triene = -360kJmol-1
ΔH Benzene = -208kJmol-1
Enthalpy change hydrogenation
χ
helliphellip
bull Benzene lower in energy by 150kJbull More stable due to delocalization of π electrons
150kJ-150
C-CSingle bond
C=CDouble bond
C=CBenzene
Bond lengthpm 154 134 140
Bond enthalpykJmol-1
346 614 507
3 Evidence for Benzene structure1
2
Click here evidence against Kekule
bull X ray hit benzene crystalbull Interact with electron (electron density
map) bull X ray diffraction producedbull Bond length measured
X ray crystallography
NO singledouble bond detected
3 Addition reaction for unsaturated C=C
Addition reaction
Substitution reaction
NO double bond
Acknowledgements
Thanks to source of pictures and video used in this presentation
Thanks to Creative Commons for excellent contribution on licenseshttpspaceplacenasagovgreenhouseenhttpwwwozonedepletioninfoeducationpart3ozonesourceshtmlhttpcreativecommonsorglicenseshttpwwwciesinorgdocs011-462011-462htmlhttpwwwepmagazineorgstorage165benzene-evidenceaspx
Prepared by Lawrence Kok
Check out more video tutorials from my site and hope you enjoy this tutorialhttplawrencekokblogspotcom
Acknowledgements
Thanks to source of pictures and video used in this presentation
Thanks to Creative Commons for excellent contribution on licenseshttpspaceplacenasagovgreenhouseenhttpwwwozonedepletioninfoeducationpart3ozonesourceshtmlhttpcreativecommonsorglicenseshttpwwwciesinorgdocs011-462011-462htmlhttpwwwepmagazineorgstorage165benzene-evidenceaspx
Prepared by Lawrence Kok
Check out more video tutorials from my site and hope you enjoy this tutorialhttplawrencekokblogspotcom