New Way Chemistry for Hong Kong A-Level Book 3A1 1 R, R’ = alkyl groups with 4-15 carbon atoms 鄰苯二甲酸酯 (phthalate ester) PAE benzoic acid ( 苯甲酸 )

New Way Chemistry for Hong Kong A-Level Book 3A11

R, R’ = alkyl groups with 4-15 carbon atoms

鄰苯二甲酸酯 (phthalate ester)

O

O

OR

OR' PAE

benzoic acid (苯甲酸 )OH

O


R, R’ = alkyl groups with 4-15 carbon atoms


O

O

OR

OR'Used as plasticiser

Potential carcinogen

New car smell

ortho-phthalic acid

benzene-1,2-dicarboxylic acid (鄰苯二甲酸 )

OH

O

O

OH



O

O

OR

OR'Used as plasticiser

Potential carcinogen

Endocrine disruption

New car smell


O

O

O

O

CH3

CH3

O

O

O

O

CH3

CH3

dibutyl benzene-1,2-dicarboxylate

butyl pentyl benzene-1,2-dicarboxylate

space

space


O OH

O

OH

O OH

O OH

isophthalic acid

meta-phthalic acid

間苯二甲酸

terephthalic acid

para-phthalic acid

對苯二甲酸benzene-1,3-dicarboxylic

acid

benzene-1,4-dicarboxylic

acid


CC

O

OH

O

HOn + O C C OH Hn

C

O

O C C OC

O

n

+ (2n - 1)H2O

H

H

H

H

H

H

H

H

polyesterpolyester

Ester Ester linkaglinkagee

(terylene)(terylene)


C

O

O C C O

H

H

H

H

C

O

n

PPolyolyeethylene thylene teterephthalaterephthalate

PET or PETEPET or PETE

CHCH22CHCH2 2 = ethene = = ethene = ethyleneethylene


IsomerismIsomerism


IsomerismIsomerism

Compounds having the same molecular formula but different linkages or spatial arrangements of atoms

Occurs when certain compounds, having the same molecular formula, exist in different forms.

IsomersIsomers


Two main types of isomerism:

1. Structural isomerism

– different linkages of atoms.

2. Stereoisomerism

–different spatial arrangements of atoms

IsomerismIsomerism


Two main types of isomerism:

1. Structural isomerism

– different linkages of atoms.

IsomerismIsomerism

Same molecular formula

Different structural formulae


2. Stereoisomerism

–different spatial arrangements of atoms

IsomerismIsomerism

Same molecular formula

& structural formulae


Categories of Categories of IsomerismIsomerism

Optical isomerismp.24


Categories of Categories of IsomerismIsomerism

Optical isomerism

Diastereoisomerism

Stereoisomerism

Geometrical isomerism

EnantiomerismOptical isomers

that are NOT mirror images of

each other

Optical isomers that are mirror images of each

other


Structural Structural IsomerismIsomerism


1. Chain isomerism1. Chain isomerism

due to the presence of different carbon skeletons.


1. Chain isomerism1. Chain isomerism

C6H14p.2, Q.2


1. Chain isomerism1. Chain isomerism• Different physical properties

b.p. : Straight-chain > branched-chain

Reason : - larger surface area and thus stronger v.d.w. forces

>



-20°C -136°C

>

m.p. : Symmetry of molecule

Packing efficiency

m.p.



-20°C -136°C

>

Notes on ‘Bonding and Structure’

p.81, Q.61


Chain isomers have different physical properties. What about their chemical properties? Would they be different as well?

Chain isomers have similar chemical properties because they have the same functional groups.


2. Position isomerism2. Position isomerism

Same carbon skeleton

Different positions of functional groups


2. Position isomerism2. Position isomerisme.g. Butan-1-ol and butan-2-ol

(molecular formula: C4H10O)


Wrong !

Q.15

Are they position isomers ?

They are chain isomers


3. Functional Group Isomerism3. Functional Group Isomerism

Due to the presence of different functional groups


Functional Group IsomerismFunctional Group Isomerism

C

H

H

H

C

H

H

O H C O C HH

H

H

H

H

Alcohol EtherVs

C2H6O



H C

H

H

C

H

H

C

H

O

H C C C H

O H

H

H

H

Aldehyde KetoneVs

C3H6O



Carboxylic acid EsterVs

C3H6O2

C

H

H

H

C C

O

OH

H

H

H C C O C H

H

H

O H

H


Position isomersPosition isomers

Chain isomer

sC5H10


Functional group isomers


4. Metamerism4. Metamerism

Occurs when the functional group (-oxy or –carbonyl) interrupts the main carbon skeleton at different positions


4. Metamerism4. Metamerisme.g. Methoxypropane and ethoxyethane



4. Metamerism4. Metamerisme.g. Pentan-2-one and pentan-3-one


can also be considered as position isomers


OH

OHPosition isomers

OH

OHPosition isomers

Chain isomers

C4H10O


OH

OHPosition isomers

Metamers

functional group isomers

O O

C4H10O


5. Tautomerism5. Tautomerism

Occurs when functional group isomers are in dynamic equilibrium with each other.



ethenol ethanal

enol – keto tautomeris

m

C C

H

H

H

OH

C C

H

H

H

H

O



ethenol ethanal

Enol is a structure with –OH attached directly to doubly-bonded C

C C

H

H

H

OH

C C

H

H

H

H

O



Not an enol

OH

But-2-en-1-ol

Does not exhibit tautomerism


C

H

O

H

H H

C

H

H

O

H

H

Which one, the enol form or the keto form, is the stronger acid ?

The enol form is the stronger acid because

the H attached to the more electronegative O can be released as H+ more easily.

Q.16


C

H

H

H

O

C

H

O

More stable Less stable

C

H

O

H

H H

C

H

H

O

H

H

Less stable

More stable

The equilibrium position lies to the right

stronger acid weaker acid

Q.16


StereoisomerStereoisomerismism


StereoisomerisStereoisomerismm

occurs when compounds having the same structural formula show different spatial arrangements of atoms.



Two categories of stereoisomerism:

1. Geometrical isomerism

2. Optical isomerism


Geometrical IsomerismGeometrical Isomerismarises from restricted rotation about a C=C double bond.



cannot be inter-converted at lower

temperatures


Rotation about the axis of a double bond through an angle of 90o results in the breaking of the π

bond

maximum overlap of pz orbitals

minimum overlap of pz orbitals


Geometrical Isomerism - CriteriaGeometrical Isomerism - Criteria

d

c

b

a

where a b and c d


E/Z notation

If there are three or four different groups attached to the Cs of C=C double bond

E/Z notation rather than the cis/trans notation is used to name the stereoisomers of a molecule.

E : in opposition to trans

Z : together cis

http://en.wikipedia.org/wiki/Cahn-Ingold-Prelog_priority_rule


Q.17

Cl

H

H

H

H

Cl

H

H

Rotate the molecular plane w.r.t. the axis

by 180

180

The same

a = b


Q.17

H

H

Cl

Cl

Cl

Cl

H

H

180

The same

a = b and c = d


Properties of Geometrical IsomersProperties of Geometrical IsomersThey have significantly different physical properties

H

Cl

H

Cl

H

H

Cl

Cl

m.p. 80C 50C

b.p. 60C 48C

1.


H

Cl

H

Cl

H

H

Cl

Cl

Zero net dipole

moment

van der Waals’ forces : cis > trans

b.p. depends on v.d.w. forces ONLY

b.p. : cis > trans


H

H

Cl

Cl

54

H

Cl

H

Cl

more symmetrical less symmetrical Two planes of

symmetryThree planes of

symmetry


H

Cl

H

Cl

H

H

Cl

Cl

more symmetrical less symmetrical

m.p. is more affected by symmetry of molecules.

m.p. : trans > cis

higher packing efficiency

lower packing efficiency


H COOH

H COOH

H COOH

HOOC H

2.

m.p. 130C << 290C


OH

O

O

OH

less extensive intermolecular hydrogen bond


intra-molecular hydrogen bond


OH

O

O

OH



weaker v.d.w. forces +

lower packing efficiency

much lower m.p.


Some geometrical isomers exhibit significantly different chemical properties1. H COOH

H COOH

H COOH

HOOC H

K1 1.4102 mol dm3 >> 9.3105 mol dm3

K2 8.0107 mol dm3 < 3.6105 mol dm3


O

O

H

OH

O

Formation of intra-molecular hydrogen bond helps to draw electrons from the –OH Weakening O – H

Ease of release of H+

H+

K1 : cis > trans


O

OH

O

O

In other words, the conjugate base is stabilized

Furthermore, the -ve charge produced is stabilized by forming intra-molecular hydrogen bond.

K1 : cis >> trans


O

O

O

O

O

O

H

H

O

O

significant repulsion

repulsion is minimized

K2 : trans >> cis


H COOH

H COOH

H COOH

HOOC H

Solubility in water

(gram of solute per 100 g of water at 25°C)

78.8 0.7

Intra-molecular hydrogen bonds in cis-isomer reduce the extent of formation of intermolecular hydrogen bonds.

Thus, water molecules can separate the acid molecules of the cis-isomer more easily

solubility of the cis-isomer in water is higher

Q.18


C

C

H C

C H

OH

O

HO

O

2.Thermal dehydration of butenedioic acid

150°C

250°C-H2O -H2O

250°Cbreaking and forming of

bond by rotating by 180° about the axis of the C=C double bond

C

C

C H

C H

HO

O

HO

O

C

C

H

H

O

C

O

O


plane-polarized light

Light vibrating in ALL possible planes Light vibrating in

only ONE plane


Optically active

Optically active substance can rotate the plane of polarization of plane-polarized light

Measured by a polarimeter.


Optically active

Dextrorotatory(+) : clockwise (to the right)

Laevorotatory(-): anti-clockwise (to the left)Is the above sample dextrorotatory ?

No. It is laevorotatory


Optical activity arises from

lack of symmetry

asymmetry (不對稱 )

chirality (手性 )

E.g. A molecule with an sp3 carbon atom bonded to FOUR different groups


The molecule has no plane or axis or center of symmetry.

It is asymmetric


It is not superimposable with its mirror image

It exhibits chirality

mirror



C

OH

H CH3

C2H5 C

OH

HH3C

C2H5

Enantiomers (對映異構體 )

Mirror images of each other

Non-superimposable with each other

Rotate plane-polarized light to the same extent but in opposite directions


C

OH

H CH3

C2H5 C

OH

HH3C

C2H5


The direction of optical rotation cannot be predicted from the structural formulae.

It can only be determined experimentally.


C

OH

H CH3

C2H5 C

OH

HH3C

C2H5


(+) or (-)butan-2-ol


C

OH

H CH3

C2H5 C

OH

HH3C

C2H5* *

*C is known as the chiral center or asymmetric centre

AnimationAnimation


Q.19Indicate the asymmetric carbon atom(s) in each of the following molecules. Which of them is/are optically active ?

sp3 hybridized C atoms each bonded to THREE identical H atoms

Not asymmetric


sp2 hybridized C atoms are NOT chiral centers



The molecule can be cut into two identical halves by the molecular plane

It has a plane of symmetry

It is NOT asymmetric



OH

Br

Br

sp3 hybridized C atom bonded to three identical H atoms

Not asymmetric



OH

Br

Br

sp3 hybridized C atom bonded to two identical Br atoms

Not chiral



OH

Br

Br

sp3 hybridized C atom bonded to two identical H atoms

Not chiral



OH

Br

Br

sp3 hybridized C atom bonded to two identical H atoms

Not chiral



Br

Br

sp3 hybridized C atoms bonded to three identical H atoms

Not chiral



Br

Br

sp3 hybridized C atom bonded to two identical CH3 groups

Not chiral



Br

Br

bromo

ethyl

(1-bromoisopropyl)

H



Br

Br

sp3 hybridized C atom bonded to four different groups

*Asymmetric

Optically active(+) or (-)



OH

OH

sp3 hybridized C atoms bonded to three identical H atoms

Not chiral



OH

OH

sp3 hybridized C atoms bonded to four different groups



OH

OH

H

methyl

hydroxy(1-hydroxyethyl)



OH

OH Hmethyl

hydroxy(1-hydroxyethyl)



OH

OH

**Two chiral centers but

optically inactive



OH

HO

free rotation about the axis of bond

The molecule has a plane of symmetry

Not asymmetric

OHHO



OHHO

The optical rotation caused by the left chiral center is cancelled by the optical rotation caused by the right chiral center.


Meso compoun

d

internal cancellation


A meso compound is a compound whose molecules contain 2 or more asymmetric atoms but is optically inactive.


Two identical groups attached to the carbon

Not asymmetric

The same



The molecule has a plane of symmetry

Not asymmetric



Br

Br

Four different groups attached to the carbon

asymmetric

Not the same



*

*

Optically inactive

A meso compound



Optically inactive

A meso compound

**



Properties of enantiomers

Identical physical properties except their optical activities.

(+)butan-2-ol (-)butan-2-ol

m.p. 99.5C 99.5C


Properties of enantiomers

Identical chemical properties except their reactions with optically active substances.


Racemic mixture (racemate)

An equimolar mixture of a pair of enantiomers

Opically inactive

The clockwise rotation caused by the (+)isomer is cancelled by the anti-clockwise rotation caused by the (-)isomer

external cancellation


Racemic mixture (racemate)

The (+)isomer and (-)isomer are different structures

One serves as the impurity of the other in a racemic mixture.

A racemic mixture has a lower m.p. than its components.

(+)butan-2-ol (-)butan-2-ol ()butan-2-ol

m.p. 99.5C 99.5C <99.5C


Identification of solid unknowns

1. By melting point determination

Determine the m.p. of the unknown and compare the result with the m.p. of known compounds


Identification of solid unknowns

2. By mixed melting point determination (more reliable)

Mix the unknown solid with a pure solid with known m.p.

Determine the m.p. of the mixture and compare the result with the m.p. of the known solid.


Q.20

Different structures may have the same melting point.

In mixed melting point determination, different structures with the same melting point behave as impurities to each other.


Structure determination of organic compoundsfrom

(i) molecular formula

(ii) reactions of functional groups (chemical properties)

(iii) physical properties

(iv) Infra-red / Mass spectra


CxHyOwNz X(halo) H

Index of unsaturation = 2

z2y

1x

1. Acyclic with single bonds ONLY

IOU = 0

CH4 02

411 C

H

H

H

H


CxHyOwNz

Index of unsaturated = 2

z2y

1x


IOU = 0

C2H6O 02

612

O

OH


CxHyOwNz

Index of unsaturated = 2

z2y

1x


IOU = 0

C2H6ClN 02

1

2

712 Cl H

NH2

Cl

NH2

Cl

+ three more


N

Cl

NH

Cl

HN Cl

C2H6ClN


2. Acyclic with ONE double bond

IOU = 1

C2H4 12

412 C C

H

H

H

H



IOU = 1

C2H4O 12

412

H3C C

H

O

C C

H

H

H

OH



IOU = 1

CH3O2N 12

1

2

311

H3C N

O

O

HO C

NH2

O


HO C

OH

NH

H C

OH

N OH

H C

H

N O

OH

H C

N

O

OH

H

H C

O

O

NH2

H2C N

OHO

O N

OH3C

* CH3O2N

E/Z

(+)/(-)


3. With ONE triple bond

IOU = 2

C2H2 22

212

C C HH


4. One cyclic

IOU = 1

12

1216 C6H12


THREE C=C bonds + ONE ring

IOU = 4

C6H6 42

616


Q.21

180o

HH

180o

sp hybridized carbon atoms in triple bond should take a linear shape.


180o

H

sp hybridized carbon atoms in triple bond should take a linear shape.

Q.21


C

180o

3 12

The carbon atom at the 2nd position, C2, is sp hybridized it takes a linear shape.

Side-way overlap between py orbitals of C1 and C2 gives a bond between C1 and C2.

Side-way overlap between pz orbitals of C2 and C3 gives another bond between C2 and C3.

Systems with adjacent C=C bonds are less stable than conjugated systems due to a lack of delocalization of electrons.

Q.21


Q.22(a) C3H6O


613

One C=O bond or one C=C bond

O

O

H

propanone

propanal

7 isomers !

1 enol

2 enols


HO

OH

OH

OH

O

(1E)-prop-1-en-1-ol

(1Z)-prop-1-en-1-ol

Prop-1-en-2-ol

prop-2-en-1-ol

methoxyethene

C=C + OH

C=C + -O-

Q.22(a)


Q.22(b) C3H6O2


613

One C=O bond or one C=C bond

24 isomers !


O

OH

O

O

H O

O

Carboxylic acid or ester

propanoic acid

methylethanoate

ethylmethanoate

Q.22(b)


C=C + two -OH Should have ‘e’ for diol

Q.22(b)

H

H

H

OHHO

1 Prop-2-ene-1,1-diol

Prop-1-ene-1,1-diolH

HO

HO1


C=C + two -OH

OH

H

HO

OHH

HO

(1Z)-prop-1-ene-1,2-diol

(1E)-prop-1-ene-1,2-diol

OH

HHO

Q.22(b)


OH

H

H

OH1Prop-2-ene-1,2-diol

Q.22(b)


(1Z)-prop-1-ene-1,3-diol

(1E)-prop-1-ene-1,3-diolH

H

HO

OH

1

3

HH

HO OH1

3Q.22(b)


C=C + OH + -O-

1-methoxyethenol

(Z)-2-methoxyethenol

(E)-2-methoxyethenol

O

HO

H

H1

O

H

H

HO1

H

O

H

HO1

Q.22(b)


O OH

(ethenyloxy)methanol

ethenyl

oxy

Q.22(b)C=C + oxy + -OH


C=O + OH

Ketone + alcohol ketol

1-hydroxypropanone

O

OH1

Q.22(b)


Aldehyde + alcohol aldol

3-hydroxypropanal

HO O

H

1

H O

H3C HOH*

1 HO

CH3HHO *

1

(+) or (-)2-hydroxypropanal

Q.22(b)


Aldehyde + oxy Q.22(b)

H

O

O

2

2-methoxyethanal


ene + peroxyQ.22(b)

O

O

O

OH

prop-2-en-1-yl

hydroperoxide

methyl

peroxy

(methylperoxy)ethene

(methylperoxy)

Ethenyl methyl peroxide


ene + peroxyQ.22(b)

H

H

O OH

O

HH

OH

(1E)-prop-1-en-1-yl hydroperoxide

(1Z)-prop-1-en-1-yl hydroperoxide


H

HOHO

prop-1-en-2-yl hydroperoxide

Q.22(b)


C5H8

Q.22(c)

Alkyne : 3

Diene : 8


CH

CH3

CH3

CH3

CH3

CH

CH3


CH2

CH3

CH2 CH3

CH2 CH2

C

CH3CH3

C CH3CH3

pentadienes

CH2

CH3


CH3

CH2

CH2

CH3

C CH2

CH3

2-methylbuta-1,3-diene

3-methylbuta-1,2-diene


Cycloalkene : 10

Bicyclic : 2

Spiro : 1

C5H8


CH3

CH3 CH3* *


CH3CH3

CH3CH3

CH3 CH3

CH3

CH3

CH3

CH3

* *


bicyclo[2.1.0]pentane

bicyclo[1.1.1]pentane

spiro[2.2]pentane

Documents

New Way Chemistry for Hong Kong A-Level Book 3A1 1 R, R’ = alkyl groups with 4-15 carbon atoms 鄰苯二甲酸酯 (phthalate ester) PAE benzoic acid ( 苯甲酸 )