Question

(a) Explain the mechanism of nucleophilic attack on a carbonyl group of an aldehyde or a ketone.
(b) How would you bring about the following conversions?
(i) Propanone to Propene
(ii) Ethanol to 3-hydroxybutanal
(iii) Benzaldehyde to Benzophenone.

Answer 1

(a) Mechanism of nucleophilic addition reactions:
A nucleophile attacks the electrophilic carbon atom of the polar carbonyl group from a direction approximately perpendicular to the plane of sp² hybridized orbitals of carbonyl carbon. The hybridization of carbon changes from sp² to sp³ in this process and a tetrahedral intermediate is produced. The intermediate captures a proton from the medium to give the neutral product.