Question:

Which of the following pairs of compound are positional isomers?

CH3−CH2−CH2−C||O−CH3andCH3−C|HCH3−CH2−CHO

CH3−CH2−CO−CH2−CH3and(CH3)2−CH−CH2−CHO

CH3−CH2−CH2−C||O−CH3andCH3−CH2−C||O−CH2−CH3

CH3−CH2−CH2−CH2−CHOandCH3−CH2−CH2−O||C−CH3

Solution:

Position isomers differ in the position of the substituent atom or group or an unsaturated linkage in the same carbon chain. Thus, 2-pentanone and 3-pentanone (option A) are the position isomers. They differ in the position of the carbonyl group. In Option B, C, and D all are functional isomers. Hence, the correct option is (A).