Chemistry. GOC–3. Session Objectives. Session Objectives. Structural isomerism: chain, positional, functional, ring-chain, isomerism, metamerism , tautomerism Homologous series Stereoisomerism: conformational, optical and geometrical isomerism. Isomerism. Isomerism. Next slide.
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Same molecular formulae but differ in the functional groups.
CH3 CH2 OHCH3OCH3
same molecular formulae but differ in the position of the same functional group.
Disubstituted benzene has three positional isomers. e.g.
same molecular formula but the distribution of alkyl groups on either side of the functional group is dissimilar. Occurs in amines, ketones, ethers and esters.
Ring chain isomerism
Due to the difference in linkage of carbon atoms in the form of ring or open chain structure, i.e. C3H6
Existing of single compound in two readily interconvertible structures called as tautomers which appears in acid catalysed or base catalysed conditions.
Contains a keto and an enol group. For example, in the presence of an acidic or basic catalyst a rapid equilibrium is established between an aldehyde or ketone and its isomeric (tautomeric) forms.
Shows keto-enol tautomerism
Does not show keto enol tautomerism
Have the same molecular formula and structure but differ in the arrangement of atoms in space.
Conformations of Cycloalkanes
Number of geometrical isomers =2x x = No. of double bonds
For compounds with two different terminal groups
No. of geometrical isomers =23=8
Criterion for optical activity
For more than one asymmetric centres –
Note: Superimposable mirror images
2. For symmetrical molecule with even number of asymmetric centres :
Number of enantiomers = 2m–1
3. For symmetrical molecule and odd number of asymmetric centres