In which of the following compounds does the carbonyl stretch in the IR spectrum occur at the lowest wavenumber?

Name: In which of the following compounds does the carbonyl stretch in the IR spectrum occur at the lowest wavenumber?
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Question

Quizplus · Accepted Answer

Pentanamide has the carbonyl stretch at the lowest wavenumber because the presence of a nitrogen atom donating electron density through resonance to the carbonyl group decreases the double bond character of the C=O bond, thus lowering the stretching frequency.

In Which of the Following Compounds Does the Carbonyl Stretch