Carbonyl Reactions a Why do aldehydes undergo nucleophilic a

Carbonyl Reactions

a.       Why do aldehydes undergo nucleophilic addition faster than ketones? Explain based upon the transition state (applying Hammond

Solution

a) carbonyls undergo nucleophilic additions rather electrophilic additions since in carbonyl functional group i.e.(>C=O) carbon E.N value is less than that of oxygen, so, carbonyl carbon feels electron defeciency and can be attacked by nucleophile better. And between aldehydes and ketones aldehydes undergo faster nucleophilic addition than that of ketones. This is because of +Inductive effect of two alkyl groups in ketone decreases the electrophilic nature of carbonyl carbon, whereas in aldehydes only one alkyl gruop is present. b) These reactions are acid catalysed generally because lone pair of electrons on the oxygen can be donated to the H+ ion thereby electrophilic nature of carbonyl carbon is increased, which leads to faster nucleophilic addition reactions.