Aldehydes are more reactive due to both steric and electronic reasons. Sterically, the hindered approach of nucleophile to the carbonyl carbon is less in aldehydes. Electronically, aldehydes are more reactive because two alkyl groups in ketones reduce the electrophilicity of the carbonyl carbon more effectively than in aldehydes.
Why are aldehydes generally more reactive than ketones in nucleophilic addition reactions, and what factors contribute to this difference in reactivity?
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Aldehydes are generally more reactive than ketones in nucleophilic addition reactions due to the structural differences. The carbonyl carbon in aldehydes is bonded to at least one hydrogen, making it more electrophilic and susceptible to nucleophilic attack. In contrast, ketones lack this hydrogen on the carbonyl carbon, reducing their electrophilic character. The presence of the hydrogen enhances the positive charge on the carbonyl carbon, making it more attractive to nucleophiles. This difference in reactivity arises from the electron-withdrawing effect of the additional alkyl group in ketones, making the nucleophilic addition reaction less favorable compared to aldehydes.