Question

We have learned that the carbonyl oxygen is the most Lewis basic site on a carboxylic acid derivative, owing to the resonance contribution of the heteroatom attached to the carbonyl carbon. Consider the structures of the ester methyl benzoate and the amide N-methylbenzamide. Which carbonyl oxygen is more Lewis basic: the ester or the amide? HINT: consider the electron-donating ability of the heteroatom on the ester (O) vs. amide (N). Pho Ph N methyl benzoate N-methylbenzamide Answer: Explain your answer above in at least one complete sentence. Compared to the starting carboxylic acid, the corresponding ester will always have a lower melting point. A major determinant in the melting point of a compound is its ability to interact with other molecules in the crystal lattice. By esterifying your acid, what key property/intermolecular force have you eliminated from your starting acid that contributes to the lattice energy, and thus the melting point? A. London Dispersion Forces (LDF) B. Dipole-dipole interactions C. H-bond interactions D. None of the above Answer:

Answer 1

Answer

1. Carbonyl oxygen of amide is more basic than esters because N is less electronegative than Oxygen.

2. H-bond interaction is eliminated at -OH of carboxylic acid which contribute to the lattice energy and thus the melting point.

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