Question

Explain the mechanism of the following reactions:

(i) Addition of Grignard’* reagent to the carbonyl group of a compound forming an adduct followed by hydrolysis.

(ii) Acid catalysed dehydration of an alcohol forming an alkene.

(iii) Acid catalysed hydration of an alkene forming an alcohol.

Answer 1

(i) Step I: Nucleophilic addition of Grignard reagent to Carbonyl group.

Step II: Formation of carbocation: It is the slowest step and hence, the rate determining step.

To drive the equilibrium to the right, ethylene is removed as it is formed.

Mechanism
Step I: Protonation of alkene to form carbocation by electrophilic ** of H3O+.