JEE Main · 2023 · 24 Jan 2023 · Shift 1 · Aldehydes Ketones and Carboxylic Acids

4-Chloroacetophenone adds hydrogen cyanide across its carbonyl in the presence of cyanide and acetic acid, giving the cyanohydrin P, a carbon bearing a hydroxyl, a methyl and a nitrile. Warming with ethanol and acid converts the nitrile into the ethyl ester, so Q is ethyl $2$-(4-chlorophenyl)-$2$-hydroxypropanoate. Two equivalents of methylmagnesium bromide then act on the ester group, which after aqueous work-up becomes a tertiary alcohol carrying two methyls, while the aromatic chlorine is left untouched. The product R is the vicinal diol $4\text{-}\mathrm{Cl}{\mathrm{C}}_6{\mathrm{H}}_4-\mathrm{C}(\mathrm{OH})(\mathrm{C}{\mathrm{H}}_3)-\mathrm{C}(\mathrm{OH})(\mathrm{C}{\mathrm{H}}_3{)}_2$.