CHEMISTRY PRESENTATIONBY:-MOIN KHAN HUSSAIN

UID:-14BBT1129

Isomerism

Isomerism

ISOMERS are compounds with the same molecular formula

(but different arrangements of atoms)

Types of Isomerism

1. Structural isomerism2. Stereoisomerism

• Geometric (cis/trans)• Optical

1. Structural isomerism

Structural Isomerism

C2H6O

These two compounds These two compounds are structural isomersare structural isomers

methoxymethane ethanol

Structural IsomerismCH3

N+

O-

O CH3

N+

O-

O

Structural isomers often have Structural isomers often have different chemical & physical different chemical & physical propertiesproperties

CH3

N+

O-

O

o– m– p–

–nitromethylbenzene

Exercise

Q What two compounds, with different functional groups, are isomers with the formula:

C3H6O2

AnswerA carboxylic acid

CH3 OH

O

CH3

O

CH3

O

An ester

2. Stereoisomerism

a. Geometric isomerism

Geometric Isomerism (cis/trans)

If two compounds have the same formulae and the same structural framework, but differ in the spatial arrangement of different atoms or groups about a central atom

CH3CH3

H H

CH3

CH3

H

H

Geometric Isomerism (cis/trans)

or about a double bond,

Geometric Isomerism (cis/trans)

then the compounds are called GEOMETRIC ISOMERS

– Cis– on the same side– Trans– on the opposite side

Geometric Isomerism (cis/trans)

[Pt(NH3)2Cl2]

CisCis––diamminedichloroplatinum(II) diamminedichloroplatinum(II) TransTrans––diamminedichloroplatinum(II)diamminedichloroplatinum(II)

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Geometric Isomerism (cis/trans)

There is restricted rotation about a C=C double bond and the two isomers are not inter-convertible without first breaking the C=C bond

Cis-but-2-ene

Trans-but-2-ene

CH3CH3

H H

CH3

CH3

H

H

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Geometric isomerism helps you see!

This reaction is the central feature of human This reaction is the central feature of human visionvision

11-cis-retinal

11-trans-retinal

11 12

R R’

R’ 11 12

RCis Trans

O

CH3

CH3CH3CH3

CH3

H

O

CH3

CH3CH3CH3 CH3 HL ig h t

2. Stereoisomerism

b. Optical isomerism

Optical Isomerism

Optical isomerism is caused by a lack of symmetry in a molecule’s structure so that the molecule and its mirror image are actually different –like a left hand and a right hand:

They are non-superimposable

For example

Nonsuperimposable mirror images

Optical isomersare called

ENANTIOMERENANTIOMERSS

EnantiomersLabels L– and D– are given

to two enantiomers to distinguish them from

each other

OH

OH O

OHNH2

H

Only one optical isomer of DOPA called L-DOPA, is effective in the treatment of Parkinson’s disease

Asymmetric Carbon

A compound that is NOT SUPERIMPOSABLE on its mirror image is described as being CHIRAL

Many chiral compounds contain an asymmetric carbon atom – a carbon atom with FOUR different groups attached

CHIRAL Carbon

For example – limonene

CH3

CH2

CH3

H

Lemons Oranges

CH3

CH2

CH3

H

For example – limonene

Lemons Oranges

CHIRAL CCHIRAL C