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JEE Main levelSingle correct optionDifficulty 2 of 3bm090

The peptide bond $- CO - NH X^{-}$ has partial double-bond character and the six atoms around it lie in one plane. The cause is

Asteric repulsion between the two alpha-carbon atoms
Bsp $^{3}$ hybridisation of the nitrogen atom
Cresonance delocalisation of the nitrogen lone pair into the carbonyl group
Dhydrogen bonding between N-H and C=O of the same bond

Answer: C

The nitrogen lone pair is delocalised onto the carbonyl:

O = C - N O X^{-} - C = N X^{+}

, so the C-N bond acquires double-bond character, rotation about it is restricted, and the amide unit is planar (trans in most cases).

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