JEE Main · 2021 · 18 Mar 2021 · Shift 1 · Haloalkanes and Haloarenes

A ${\mathrm{C}}_8{\mathrm{H}}_8\mathrm{O}$ compound that reacts with a Grignard reagent at a carbonyl is acetophenone, ${\mathrm{C}}_6{\mathrm{H}}_5\mathrm{COC}{\mathrm{H}}_3$. Addition of ${\mathrm{C}}_2{\mathrm{H}}_5\mathrm{MgBr}$ followed by hydrolysis puts an ethyl group on the carbonyl carbon and gives the tertiary alcohol ${\mathrm{C}}_6{\mathrm{H}}_5\mathrm{C}(\mathrm{OH})(\mathrm{C}{\mathrm{H}}_3){\mathrm{C}}_2{\mathrm{H}}_5$, which is A and has the formula ${\mathrm{C}}_{10}{\mathrm{H}}_{14}\mathrm{O}$. A tertiary benzylic alcohol ionises at once with Lucas reagent because the resulting carbocation is both tertiary and benzylic, so the chloride separates immediately. B is 2-chloro-2-phenylbutane, ${\mathrm{C}}_6{\mathrm{H}}_5\mathrm{C}(\mathrm{Cl})(\mathrm{C}{\mathrm{H}}_3){\mathrm{C}}_2{\mathrm{H}}_5$, of formula ${\mathrm{C}}_{10}{\mathrm{H}}_{13}\mathrm{Cl}$.