JEE Main · 2021 · 25 Jul 2021 · Shift 2 · Aldehydes Ketones and Carboxylic Acids

One equivalent of the Grignard reagent adds to the carbon of the nitrile group, and the magnesium salt of the ketimine so formed is hydrolysed by aqueous acid to a ketone:

P is thus acetophenone, a methyl ketone. A $\mathrm{C}{\mathrm{H}}_3$ group bonded to a carbonyl carbon is halogenated three times by ${\mathrm{I}}_2$ in alkali and the $\mathrm{C}{\mathrm{I}}_3$ group then leaves as a yellow precipitate of iodoform. Schiff's and Tollens' tests both require a free $-\mathrm{CHO}$ group and the ninhydrin test requires an $\alpha$-amino acid, none of which acetophenone possesses. Acetophenone therefore gives a positive iodoform test.