When determining the primary structural isomeric relationship between pentan-2-one and pentan-3-one, — Isomerism and Stereochemistry Chemistry Question

💡 Solution & Explanation

The FMCP Priority Rule dictates the hierarchy for naming structural isomers: Functional > Metamerism > Chain > Positional. Both pentan-2-one and pentan-3-one differ in the position of the carbonyl group, but they also differ in the alkyl groups attached to the polyvalent $-CO-$ group (methyl/propyl vs. ethyl/ethyl). Because Metamerism (M) strictly overrules Positional (P) isomerism in the hierarchy, they are officially classified as Metamers.