Which of the following pairs of compounds does NOT represent a pair of functional isomers?

Step-by-step solution

Functional isomers have the same molecular formula but different functional groups. (1) Butan-1-amine is a 1^ amine, while N-methylpropan-1-amine is a 2^ amine. Amines of different degrees are considered different functional groups, so they are functional isomers. (2) Butanamide is a 1^ amide, while N-methylpropanamide is a 2^ amide. Like amines, amides of different degrees are different functional groups, making them functional isomers. (3) Propanoic acid is a carboxylic acid, while methyl ethanoate is an ester. T