Question

Which is a correct statement?

A. The delocalization energy of an ester is about 18 kcal/mol, and the delocalization energy of an amide is about 10 kcal/mol.

B. The delocalization energy of an ester is about 10 kcal/mol, and the delocalization energy of an amide is about 18 kcal/mol.

Short answer

The statement B is correct, that is, the resonance energy of an amide is about 18 kcal/mol and the resonance energy of an ester is about 10 kcal/mol.

Step-by-step solution

Step-by-Step Solution Step 1: Resonance

More the resonance, more will be the stability of the resonance structure. The positive charge is more stabilized on the less electronegative element.

Delocalization energy

Esters and amides each have two resonance contributors. The resonance contributor makes a greater contribution to the hybrid in the amide than in the ester. This is due to the fact that the amide’s resonance contributor is more stable because nitrogen, being less electronegative than oxygen, can better accommodate a positive charge.

Ester

Resonance for ester

Amide

Resonance for amide

The amide is with a resonance of around 18 kcal/mol and it is higher than the corresponding ester due to the less electronegativity of nitrogen. The lone pair on nitrogen involves resonance. The involvement of a lone pair is easier in the resonance. Hence, the resonance energy is more and it also gains more stability.

Thus, statement B is correct that the resonance energy of an amide is about 18 kcal/mol and the resonance energy of an ester is about 10 kcal/mol.