Question

Differentiate between chain and position isomerism using suitable examples.

Answer 1

Feature	Chain Isomerism	Position Isomerism
Definition	Compounds with the same molecular formula but different arrangements of the carbon skeleton (straight vs. branched).	Compounds with the same molecular formula and carbon skeleton, but a different location of the functional group/double bond.
Parent Carbon Chain	Changes in length or branching style.	Stays exactly the same length.
Position of Group/Bond	Stays the same relative to the chain type.	Changes to a different carbon atom number.
Example Name	Butane (C4H10) isomers	Butene (C4H8) isomers
Isomer 1	n-Butane (4-carbon straight chain): \(\text{CH}_3-\text{CH}_2-\text{CH}_2-\text{CH}_3\)	But-1-ene (Double bond at carbon-1): \[\ce{\overset{1}{\text{CH}_2} = \overset{2}{\text{CH}} - \overset{3}{\text{CH}_2} - \overset{4}{\text{CH}_3}}\]
Isomer 2	Isobutane (3-carbon chain with a branch): \[\begin{array}{cc} \phantom{..}\ce{CH3}\\ |\phantom{..}\\ \ce{CH3 - CH - CH3}\\ \end{array}\]	But-2-ene (Double bond at carbon-2): \[\ce{\overset{1}{\text{CH}_3} - \overset{2}{\text{CH}} = \overset{3}{\text{CH}} - \overset{4}{\text{CH}_3}}\]