Structural isomerism.

Isomerism- Definition, type.

1. STRUCTURAL ISOMERISM
IN ORGANIC COMPOUNDS
Nidhi Sharma

2. STRUCTURAL ISOMERISM IN ORGANIC COMPOUNDS
Isomerism in organic chemistry is a phenomenon shown by two or
more organic compounds having the same molecular formula but
different properties due to difference in arrangement of atoms along the
carbon skeleton (structural isomerism) or in space (Stereo isomerism).
The chart summarizes the types of isomerism, and we will discuss
only structural isomerism in greater detail.
STRUCTURAL ISOMERISM
1. Chain Isomerism-
It occurs when carbon atoms are linked to the main chain in different
ways. For example:
Figure 2. Pentane chain isomers

3. Position Isomerism-
It occurs when functional groups are attached on different
positions on a carbon chain. For example:
Figure 3. Positionisomerism
2. Functional Isomerism
Itisaveryinterestingformofisomerismwherethecompoundsare
differentduetodifferentarrangementsofatomsleadingtodifferent
functionalgroups.Asfunctionalgroupsareusuallythereactivecentre
ofamoleculethisleadstoentirelydifferentproperties.Forexample:
Figure 4. Functional isomerism
3. Metamerism Butyraldehyde
Thisformofisomerismisrareandislimitedto
moleculeshavingadivalentatomlikeOorSandalkyl
groupsaroundit.Themainexamplescomefromethers
andthioethers.

4. Figure 5. Metamerism
4. Tautomerism
Thisisomerismisduetospontaneousintreconversionoftwoisomericforms
withdifferentfunctionalgroups.Theprerequisitesforthisisthepresenceofthe
C=O,C==NorN=OintheusualcasesandanalphaHatom.Themostusualis
the‘keto-enol’tautomerism,buttherecanbeotherslikenitro-aciandamine-
imineforms.
Figure 6. Tautomerism
IngeneraltheKetoformismorestable.Enolscanbeformsbyacidorbase
catalysisfromtheketoneandareextensivelyusedinmakingC-Csinglebonds
inorganicsynthesis.
5. Ring-Chain isomerism
Hereoneisomerisanopenchainmoleculeandtheotheracyclicmolecule.
Figure 7. Ring-chain isomerism
Propaneisanalkeneandcyclopropaneanalkane,twodifferentof
compounds.
Butanol
.

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