2 CH241 Polar Covalent Bonds

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2. Polar Covalent Bonds:

Acids and Bases

Why this chapter?

Description of basic ways chemists account for

chemical reactivity.

Establish foundation for understanding specificreactions discussed in subsequent chapters.



2

2.1 Polar Covalent Bonds:

Electronegativity

Covalent bonds can have ionic character

These are polar covalent bonds

◦ Bonding electrons attracted more strongly by oneatom than by the other

◦ Electron distribution between atoms is notsymmetrical



3

Bond Polarity and Electronegativity

Electronegativity (EN): intrinsic ability of an atomto attract the shared electrons in a covalent bond

Differences in EN produce bond polarity

Arbitrary scale. As shown in Figure 2.2,electronegativities are based on an arbitrary scale

F is most electronegative (EN = 4.0), Cs is least(EN = 0.7)

Metals on left side of periodic table attract electronsweakly, lower EN

Halogens and other reactive nonmetals on rightside of periodic table attract electrons strongly,higher electronegativities

EN of C = 2.5



4

The Periodic Table and Electronegativity



5

Bond Polarity and Inductive Effect

Nonpolar Covalent Bonds: atoms with similar EN

Polar Covalent Bonds: Difference in EN of atoms <2

Ionic Bonds: Difference in EN > 2

◦ C –H bonds, relatively nonpolar C-O, C-X bonds(more electronegative elements) are polar

Bonding electrons toward electronegative atom

◦ C acquires partial positive charge, +

◦ Electronegative atom acquires partial negativecharge, -

Inductive effect: shifting of electrons in a bond inresponse to EN of nearby atoms



CO O

Polarity, Shape

3.5 3.52.5

O=C=O

+ --

Polar Covalent Bonds

Linear Shape (180o)

Electronegativity

Difference

< 0.5

Nonpolar

0.5

-

1.7

Polar

>

1.8

Ionic

Nonpolar Compound

CO2



CH H

O

Polarity, Shape

O=C=O+ --

e-’s in 2 directions = 180

o

Linear

e-’s in 3 directions = 120o

+

-

Trigonal planar

Nonpolar Compound

Polar Compound



F

F B

Polarity, Shape

4.0

4.0

2.0 +

- -

Polar Covalent Bonds

(120o)Trigonal Planar

Nonpolar Compound

BF3

F 4.0F

B

F

F-



Polarity, Shape

CH H

H

Cl

CH H

H

ClH

CH

ClH

OH H

H-O-H

O

H

H

+

+-

+-

e-’s in 4 directions = 109.5o

Tetrahedral

Bent

4 directions = 109.5o



Polarity, Shape

NH H

H +

-

e-’s in 4 directions = 109.5o

Pyramidal

NH H

H

NH

H+

+

(109.5o)Tetrahedral Configuration of Electrons

Trigonal Pyramid Configuration of Atoms



Tetrahedral electron-pair

Geometries

Tetrahedral

PyramidalBent



Electrostatic Potential Maps

Electrostatic potentialmaps show calculated

charge distributions

Colors indicate electron-

rich (red) and electron-

poor (blue) regions

Arrows indicate

direction of bondpolarity



2.2 Polar Covalent Bonds: Dipole Moments Molecules as a whole are often polar from vector summation of

individual bond polarities and lone-pair contributions

Strongly polar substances soluble in polar solvents like water;nonpolar substances are insoluble in water.

Dipole moment () - Net molecular polarity, due to difference insummed charges

◦ - magnitude of charge Q at end of molecular dipole timesdistance r between charges = Q r, in debyes (D), 1 D = 3.336 1030 coulomb meter

length of an average covalent bond, the dipole moment would be 1.60 1029 Cm, or 4.80 D.



17

Dipole Moments in Water and Ammonia

Large dipole moments

◦ EN of O and N > H

◦ Both O and N have lone-pair electrons oriented awayfrom all nuclei



18

Absence of Dipole Moments

In symmetrical molecules, the dipole moments of

each bond has one in the opposite direction

The effects of the local dipoles cancel each other



Which of the above molecules is the most

polar?

1. A

2. B

3. C4. D

5. It cannot be

determined

F

H

H

F

F

H

F

H

H

H

F

F

F

F

F

F

A B C D

Learning Check:



Which of the above molecules is the most

polar?

1. A

2. B

3. C4. D

5. It cannot be

determined

F

H

H

F

F

H

F

H

H

H

F

F

F

F

F

F

A B C D

Solution:



Learning Check:

21

Which of the following molecules isnonpolar?

1.H2O

2. CH3CN

3. CHCl3

4. CH2Cl25. CO2



Solution:

22

Which of the following molecules isnonpolar?

1.H2O

2. CH3CN

3. CHCl3

4. CH2Cl25. CO2



Which of the above molecules has (have) a

dipole moment?

1. A only

2.B only

3. C only

4. A and B

5. B and C

F

F

H

H

C

F

H

H

F

C C

F

H

A B C

H

F

Learning Check:



Which of the above molecules has (have) a

dipole moment?

1. A only

2.B only

3. C only

4. A and B

5. B and C

F

F

H

H

C

F

H

H

F

C C

F

H

A B C

H

F

Solution:



25

2.3 Formal Charges Sometimes it is necessary to have structures with formal charges

on individual atoms We compare the bonding of the atom in the molecule to the

valence electron structure

If the atom has one more electron in the molecule, it is shownwith a ―-‖ charge

If the atom has one less electron, it is shown with a ―+‖ charge

Neutral molecules with both a ―+‖ and a ―-‖ are dipolar



26

• Atomic sulfur has 6

valence electrons.

Dimethyl suloxide

sulfur has only 5.

• It has lost an electron

and has positive

charge.

• Oxygen atom in

DMSO has gained

electron and has (-)

charge.

Formal Charge for Dimethyl Sulfoxide



27



What are the hybridization and a formalcharge, respectively, on boron in BH4

–?

1. sp3, 02. sp3, –1

3. sp3, +1

4. sp2, –1

5. sp2, +1

Learning Check:



What are the hybridization and a formalcharge, respectively, on boron in BH4

–?

1. sp3, 02. sp3, –1

3. sp3, +1

4. sp2, –1

5. sp2, +1

Solution:



30

2.4 Resonance Some molecules are have structures that cannot be shown with

a single representation In these cases we draw structures that contribute to the final

structure but which differ in the position of the bond(s) or lonepair(s)

Such a structure is delocalized and is represented byresonance forms

The resonance forms are connected by a double-headed arrow



31

Resonance Hybrids A structure with resonance forms does not alternate between

the forms Instead, it is a hybrid of the two resonance forms, so the

structure is called a resonance hybrid

For example, benzene (C6H6) has two resonance forms withalternating double and single bonds

◦

In the resonance hybrid, the actual structure, all its C-Cbonds are equivalent, midway between double and single



32

2.5 Rules for Resonance Forms

Individual resonance forms are imaginary - thereal structure is a hybrid (only by knowing the

contributors can you visualize the actual structure)

Resonance forms differ only in the placement of

their or nonbonding electrons Different resonance forms of a substance don’t

have to be equivalent

Resonance forms must be valid Lewis structures:

the octet rule applies The resonance hybrid is more stable than any

individual resonance form would be



33

Curved Arrows and Resonance Forms We can imagine that electrons move in pairs to

convert from one resonance form to another A curved arrow shows that a pair of electrons moves

from the atom or bond at the tail of the arrow to theatom or bond at the head of the arrow



34

2.6 Drawing Resonance Forms

Any three-atom grouping with a multiple

bond has two resonance forms



35

Different Atoms in Resonance Forms Sometimes resonance forms involve different atom types as

well as locations The resulting resonance hybrid has properties associated with

both types of contributors

The types may contribute unequally

The ―enolate‖ derived from acetone is a good illustration, withdelocalization between carbon and oxygen



36

2,4-Pentanedione

The anion derived from 2,4-pentanedione◦ Lone pair of electrons and a formal

negative charge on the central carbon

atom, next to a C=O bond on the left and onthe right

◦ Three resonance structures result



Which of the following statements is falseconcerning resonance structures?

1. The arrangement of nuclei in all contributing structures

must be the same.2. The arrangement of electrons in each contributing

structure is different.

3. Each atom in a contributing structure must have a

completed valence shell.4. The contributing structures may have different

energies.

5. All contributing structures must have the correct

number of valence electrons.

Learning Check:



Which of the following statements is falseconcerning resonance structures?

1. The arrangement of nuclei in all contributing structures

must be the same.2. The arrangement of electrons in each contributing

structure is different.

3. Each atom in a contributing structure must have a

completed valence shell.4. The contributing structures may have different

energies.

5. All contributing structures must have the correct

number of valence electrons.

Solution:



Consider all equivalent resonance structures for thecarbonate anion shown below. If the bond order is defined as

the number of electron pairs shared between two atoms,

what is the average bond order for the C-O1 bond?

1. 2

2. 3/2

3. 4/3

4. 1

5. 1/4

O

O O

1

Learning Check:



Consider all equivalent resonance structures for thecarbonate anion shown below. If the bond order is defined as

the number of electron pairs shared between two atoms,

what is the average bond order for the C-O1 bond?

1. 2

2. 3/2

3. 4/3

4. 1

5. 1/4

O

O O

1

Solution:



Consider all equivalent resonance structures for carbonate anion shown below. What is the

formal charge on O1?

1. –1

2. –2/3

3. –1/2

4. –1/3

5. 0

O

O O

1

Learning Check:



Consider all equivalent resonance structures for carbonate anion shown below. What is the

formal charge on O1?

1. –1

2. –2/3

3. –1/2

4. –1/3

5. 0

O

O O

1

Solution:



Anions with the negative charge residing on carbonsare called carbanions. In the methyl anion the carbon

is sp3 hybridized. What is the hybridization of carbon

1 in the allyl anion?

H

H

H H

H

allyl anion (a carbanion)1

1. sp3

2. sp2

3. sp

4. sp3d

5. carbon 1 is not hybridized

Learning Check:



Anions with the negative charge residing on carbonsare called carbanions. In the methyl anion the carbon

is sp3 hybridized. What is the hybridization of carbon

1 in the allyl anion?

H

H

H H

H

allyl anion (a carbanion)1

1. sp3

2. sp2

3. sp

4. sp3d

5. carbon 1 is not hybridized

Solution:



How many uncharged resonance

structures exist for the following

molecule?

1. Only the one shown above

2. 2

3. 3

4. 4

5. 5

Learning Check:



How many uncharged resonance

structures exist for the following

molecule?

1. Only the one shown above

2. 2

3. 3

4. 4

5. 5

Solution:



47

2.7 Acids and Bases: The Brønsted –

Lowry Definition

The terms ―acid‖ and ―base‖ can have different

meanings in different contexts

For that reason, we specify the usage with more

complete terminology

The idea that acids are solutions containing a lot of

―H+‖ and bases are solutions containing a lot of ―OH-‖

is not very useful in organic chemistry

Instead, Brønsted –Lowry theory defines acids and

bases by their role in reactions that transfer protons(H+) between donors and acceptors



Bronsted-Lowry theory

Acid=a Proton donor

donates a proton, H+, to solvent

Example: HCl

HCl + H2O H3O+ + Cl-

hydronium ion



Example: HNO3

HNO3 is the acid: it donates the proton.


HNO3 + H2O H3O+ + NO3

-



Base = a proton acceptor accepts a Proton, H+, from solvent

NH3

+ H2O NH

4

+ + OH-

Accepted H+


NH3 is the Base: it takes the proton.

Hydroxide ions (OH-) form when water

donates the proton.



Common Acids Battery Acid

Stomach Acid

Coca Cola

Carbonated Water

Vinegar

Citrus fruits

Vitamin C

Grapes

Aspirin

H2SO

4HCl

H3PO4

H2CO3

HC2H3O2

H3C6O7H8

HC6O6H7 H2C4O6H4

H2C9O4H8

Sulfuric AcidHydrochloric Acid

Phosphoric Acid

Carbonic Acid

Acetic Acid

Citric Acid

Ascorbic Acid Tartaric Acid

Acetyl Salicylic Acid



Naming Acids

•Binary Acids = (-ide ending)

HCl

Hydro- ______-ic Acid

= Hydrochlor ic Acid

•Oxoacids = H, Nonmetal & O -ate ending (The higher number of O’s)

= Hydrogen Chlor ide

______________-ic Acid

HNO3

= Hydrogen Nitr ate = Nitr ic Acid

-ite ending (The lower number of O’s)

______________-ous Acid

HNO2 = Hydrogen Nitr ite = Nitr ous Acid



Naming AcidsNon-Acid name Acid Name

H2SO4

H2SO3

H2S

H3PO4

HBr

H2CO3

HNO2 HNO3

Dihydrogen Sulf ate

Hydrogen Bromide

Trihydrogen Phosphate

Dihydrogen carbonate

Acetic Acid

Sulfur ic Acid

Hydrobromic Acid

Phosphor ic Acid

Dihydrogen Sulf ite

Dihydrogen Sulf ide

Sulfur ous Acid

Hydrosulfur ic Acid

Hydrogen Nitr ate

Hydrogen Nitr ite Nitr ous Acid

Nitr ic Acid

Hydrogen AcetateHC2H3O2

Carbonic Acid



Naming AcidsNon-Acid name Acid Name

H2SO4

H2SO3

H2SO2

HCl

HClO

HClO2 HClO3

Dihydrogen Sulf ate

Hydrogen Chlor ide

Hydrogen hypochlor ite

Per chlor ic Acid

Sulfur ic Acid

Hydrochlor ic Acid

Dihydrogen Sulf ite

Dihydrogen Sulf ide

Sulfur ous Acid

Hyposulfur ous Acid

Hydrogen chlor ate

Hydrogen chlor ite Chlor ous Acid

Chlor ic Acid

Hydrogen Per chlor ateHClO4

Hypochlor ous Acid



H2SO

4HCl

H3PO4

H2CO3

HC2H3O2

H3C6O7H8

HC6O6H7 H2C4O6H4

H2C9O4H8

Common AcidsBattery AcidStomach Acid

Coca Cola

Carbonated Water

Vinegar

Citrus fruitsVitamin C

Grapes

Aspirin

Strong•100% ionization•Strong electrolyte

Weak•Partial ionization

•Weak electrolyte

•Taste sour



AcidsH-Cl + H-O-H + Cl-

HO

H

H

+

HO

H

H

+Cl-

H-Cl

H+

HC2H3O2

C2H3O21-

HC2H3O2

H-C2H3O2 + H-O-HH

OH

H

+ + C2H3O2-



Base = gives hydroxide ions in water.(Arrhenius definition)

= takes hydrogen ions in water.(Bronsted-Lowry definition)

Bases

NaOH

Na+ + OH-OH-

OH-

Na+

Na+

NaOH



58

Brønsted Acids and Bases

―Brønsted-Lowry‖ is usuallyshortened to ―Brønsted‖

A Brønsted acid is a substance that

donates a hydrogen ion (H+

) A Brønsted base is a substance that

accepts the H+

◦

―proton‖ is a synonym for H+

- loss of anelectron from H leaving the bare

nucleus—a proton



59

The Reaction of Acid with Base Hydronium ion, product when base H2O gains a proton

HCl donates a proton to water molecule, yielding hydronium ion

(H3O+) [conjugate acid] and Cl [conjugate base]

The reverse is also a Brønsted acid –base reaction of the

conjugate acid and conjugate base



60

2.8 Acid and Base Strength

The equilibrium constant (K eq ) for the reaction of anacid (HA) with water to form hydronium ion and theconjugate base (A-) is a measure related to thestrength of the acid

Stronger acids have larger K eq

Note that brackets [ ] indicate concentration, molesper liter, M.



61

K a – the Acidity Constant

The concentration of water as a solvent does not changesignificantly when it is protonated

The molecular weight of H2O is 18 and one liter weighs 1000grams, so the concentration is ~ 55.4 M at 25°

The acidity constant, K a for HA K eq times 55.6 M (leaving[water] out of the expression)

K a ranges from 1015 for the strongest acids to very small values(10-60) for the weakest



62



63

pK a – the Acid Strength Scale

pK a = -log K a The free energy in an equilibrium is related to –log of

K eq (DG = -RT log K eq)

A smaller value of pK a indicates a stronger acid and

is proportional to the energy difference betweenproducts and reactants

The pK a of water is 15.74

2 9 P di ti A id B R ti



64

2.9 Predicting Acid –Base Reactions

from pK a Values pK

a

values are related as logarithms to equilibrium constants

Useful for predicting whether a given acid-base reaction willtake place

The difference in two pK a values is the log of the ratio of equilibrium constants, and can be used to calculate the extent of transfer

The stronger base holds the proton more tightly



65

2.10 Organic Acids and Organic Bases

Organic Acids:

- characterized by the presence of positively polarized hydrogen atom



66

Organic Acids Those that lose a proton from O –H, such as

methanol and acetic acid Those that lose a proton from C –H, usually from a

carbon atom next to a C=O double bond (O=C –C –H)



67

Organic Bases Have an atom with a lone pair of electrons that can

bond to H+

Nitrogen-containing compounds derived fromammonia are the most common organic bases

Oxygen-containing compounds can react as baseswhen with a strong acid or as acids with strong bases



68

2.11 Acids and Bases: The Lewis Definition

Lewis acids are electron pair acceptors and Lewisbases are electron pair donors

Brønsted acids are not Lewis acids because theycannot accept an electron pair directly (only a proton

would be a Lewis acid) The Lewis definition leads to a general description of

many reaction patterns but there is no scale of strengths as in the Brønsted definition of pK a

Lewis Acids and the Curved Arrow



69

Lewis Acids and the Curved Arrow

Formalism

The Lewis definition of acidity includes metal cations,such as Mg2+

◦ They accept a pair of electrons when they form a bondto a base

Group 3A elements, such as BF3

and AlCl3

, are Lewisacids because they have unfilled valence orbitals and canaccept electron pairs from Lewis bases

Transition-metal compounds, such as TiCl4, FeCl3, ZnCl2,and SnCl4, are Lewis acids

Organic compounds that undergo addition reactions withLewis bases (discussed later) are called electrophiles andtherefore Lewis Acids

The combination of a Lewis acid and a Lewis base canshown with a curved arrow from base to acid

Ill stration of C r ed Arro s in Follo ing



70

Illustration of Curved Arrows in Following

Lewis Acid-Base Reactions



71

Lewis Bases Lewis bases can accept protons as well as Lewis acids,

therefore the definition encompasses that for Brønsted bases Most oxygen- and nitrogen-containing organic compounds are

Lewis bases because they have lone pairs of electrons

Some compounds can act as both acids and bases, dependingon the reaction



All Lewis acids can also be classified

as Brønsted-Lowry acids.

1. True

2. False

Learning Check:



All Lewis acids can also be classified

as Brønsted-Lowry acids.

1. True

2. False

Solution:



Which statement best describes thefollowing reaction?

NH3 + BH3 H3N BH3

1. an acid-base reaction where NH3 acts as a Brønsted-Lowry acid

2. an acid-base reaction where NH3 acts as a Brønsted-

Lowry base

3. an acid-base reaction where NH3 acts as a Lewisacid

4. an acid-base reaction where NH3 acts as a Lewis

base

5. None of these adequately describes the reaction.

Learning Check:



Which statement best describes thefollowing reaction?

NH3 + BH3 H3N BH3

1. an acid-base reaction where NH3 acts as a Brønsted-Lowry acid

2. an acid-base reaction where NH3 acts as a Brønsted-

Lowry base

3. an acid-base reaction where NH3 acts as a Lewisacid

4. an acid-base reaction where NH3 acts as a Lewis

base

5. None of these adequately describes the reaction.

Solution:



What is the main reason why molecule A isless acidic than molecule B?

A: CH3CH2CH2-H B: CH3CH2O-H

1. There are more hydrogens in A.2. The C-H bond is weaker than the O-H bond.

3. The conjugate base of A is more stable than the

conjugate base of B.

4. In the conjugate base of B, the negative charge resideson a more electronegative atom.

5. There is resonance and inductive stabilization of


Learning Check:



What is the main reason why molecule A isless acidic than molecule B?

A: CH3CH2CH2-H B: CH3CH2O-H

1. There are more hydrogens in A.2. The C-H bond is weaker than the O-H bond.

3. The conjugate base of A is more stable than the


4. In the conjugate base of B, the negative charge resideson a more electronegative atom.

5. There is resonance and inductive stabilization of


Solution:



Ammonia can act as all four classifications of acids or bases (Lewis acid, Lewis base,

Brønsted-Lowry acid, and Brønsted-Lowry

base.)

1. True

2. False

Learning Check:



Ammonia can act as all four classifications of acids or bases (Lewis acid, Lewis base,

Brønsted-Lowry acid, and Brønsted-Lowry

base.)

1. True

2. False

Solution:

C



Van der Waals interactions refer to the weak attractiveforces that occur between individual molecules and are

very important in determining the shape and properties

of biological molecules such as proteins. Which of the

following play no role in van der Waals interactions?

1. hydrogen bonding

2. dispersion forces

3. dipole-dipole forces4. magnetic forces

5. All of these are important in van der Waals

interactions.

Learning Check:

S l i



Van der Waals interactions refer to the weak attractiveforces that occur between individual molecules and are

very important in determining the shape and properties

of biological molecules such as proteins. Which of the

following play no role in van der Waals interactions?

1. hydrogen bonding

2. dispersion forces

3. dipole-dipole forces4. magnetic forces

5. All of these are important in van der Waals

interactions.

Solution:

L i Ch k



Which is the correct order of the pK a values?

1. H2O > HO – > H3O+

2. HO – > H3O+ > H2O

3.H3O

+

> HO

–

> H2O4. HO – > H2O > H3O

+

5. H3O+ > H2O > HO –

Learning Check:

S l ti



Which is the correct order of the pK a values?

1. H2O > HO – > H3O+

2. HO – > H3O+ > H2O

3.H3O

+

> HO

–

> H2O4. HO – > H2O > H3O

+

5. H3O+ > H2O > HO –

Solution:

2 12 M l l M d l



84

2.12 Molecular Models

Organic chemistry is 3-D space Molecular shape is critical in determining the

chemistry a compound undergoes in the lab, and inliving organisms

2 13 N l t I t ti



85

2.13 Noncovalent Interactions

Several types:- Dipole-dipole forces

- Dispersion forces

- Hydrogen bonds

Di l Di l



86

Dipole-Dipole

• Occur between polar molecules as a result of electrostaticinteractions among dipoles

• Forces can be attractive of repulsive depending on orientation

of the molecules

Di i F



87

Dispersion Forces

• Occur between all neighboring molecules and arisebecause the electron distribution within molecules

that are constantly changing

H d B d F



88

Hydrogen Bond Forces

• Most important noncovalent interaction in biological molecules

• Forces are result of attractive interaction between a hydrogen

bonded to an electronegative O or N atom and an unshared

electron pair on another O or N atom



89

S



90

Summary Organic molecules often have polar covalent bonds

as a result of unsymmetrical electron sharing causedby differences in the electronegativity of atoms

The polarity of a molecule is measured by its dipolemoment, .

(+) and () indicate formal charges on atoms in

molecules to keep track of valence electrons aroundan atom

Some substances must be shown as a resonancehybrid of two or more resonance forms that differ by the location of electrons.

A Brønsted( –Lowry) acid donates a proton A Brønsted( –Lowry) base accepts a proton

The strength Brønsted acid is related to the -1 timesthe logarithm of the acidity constant, pK a. Weaker acids have higher pK a’s

S ( t’d)



91

Summary (cont’d)

A Lewis acid has an empty orbital that can acceptan electron pair

A Lewis base can donate an unshared electron pair

In condensed structures C-C and C-H are implied

Skeletal structures show bonds and not C or H (C

is shown as a junction of two lines) – other atomsare shown

Molecular models are useful for representingstructures for study

Noncovalent interactions have several types: dipole-

dipole, dispersion, and hydrogen bond forces

Learning Check:



Which statement about the acid-base equilibrium

shown above is incorrect?

1. the equilibrium favors the products

2. water is a conjugate acid in this equilibrium

3. hydroxide is the strongest base present4. phenol is 6 times more acidic than water

5. the negative charge in the phenoxide is resonance

stabilized

OH

+ OH

O

+ H2O

pKa = 10 pKa = 16

phenol hydroxide phenoxide

Learning Check:

Solution:



Which statement about the acid-base equilibrium

shown above is incorrect?

1. the equilibrium favors the products

2. water is a conjugate acid in this equilibrium

3. hydroxide is the strongest base present4. phenol is 6 times more acidic than water

5. the negative charge in the phenoxide is resonance

stabilized

OH

+ OH

O

+ H2O

pKa = 10 pKa = 16

phenol hydroxide phenoxide

Solution:

Learning Check:



What is the most likely product of the following Lewis

acid-base reaction?

1. A

2. B

3. C

4. D

5. E

O

O

+ BF3 product

O

O

O

O

O

O

O

OBF3 BF3

BF3 BF3

O

O BF3

A B C D E

Learning Check:

Solution:



What is the most likely product of the following Lewis

acid-base reaction?

1. A

2. B

3. C

4. D

5. E

O

O

+ BF3 product

O

O

O

O

O

O

O

OBF3 BF3

BF3 BF3

O

O BF3

A B C D E

Solution:

Learning Check:



Which of these structures is not a resonance form of

the others? (The lone pairs are not shown explicitly.)

1. a

2. b

3. c

4. d

5. e

NH

NH

N

H

N N

a) b) c) d) e)

H H

Learning Check:

Solution:



Which of these structures is not a resonance form of

the others? (The lone pairs are not shown explicitly.)

1. a

2. b

3. c

4. d

NH

NH

N

H

N N

a) b) c) d) e)

H H

Solution:

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2 CH241 Polar Covalent Bonds