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JEE Main levelSingle correct optionDifficulty 2 of 3o1134

A secondary amine and a ketone give an enamine, not an imine, because in the intermediate iminium ion

Athe nitrogen carries no proton that can be lost, so an alpha C-H proton is removed instead
Bthe nitrogen lone pair is unavailable so water cannot leave
Cthe carbon of C=N is too electron rich to be protonated
Dthe secondary amine is a weaker nucleophile than a primary amine

Answer: A

For

R X_{2} NH + R X_{2}^{'} C = O

the iminium ion is

R X_{2}^{'} C = N X^{+} R X_{2}

. It has no N-H, so it can only become neutral by losing a proton from the alpha carbon, which gives

C = C - NR X_{2}

, the enamine.

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