Why do amide bonds exist as reasonably stable s-cis or s-trans isomers at room temperature?
A)These amide bonds are not stable.
B)There is partial double bond character between the carbonyl carbon and the nitrogen atom.
C)The oxygen atom is hydrogen-bonded with the nitrogen atom.
D)The side-chains can form hydrogen bonds.

Question

Quizplus · Accepted Answer

The amide bond has partial double bond character between the carbonyl carbon and the nitrogen atom, which stabilizes the s-cis or s-trans isomers. This double bond character arises due to resonance of the two major contributing structures, where the nitrogen lone pair donates electron density into the antibonding orbital of the C=O bond, leading to a π-bond between the two atoms. This double bond character restricts rotation around the C-N bond, resulting in the stabilization of s-cis or s-trans isomers.

Why Do Amide Bonds Exist as Reasonably Stable S-Cis or S-Trans