Determine the correct decreasing order of reactivity for the following alcohols towards substitution with a mixture of NaBr and H ₂ SO ₄ : (I) (II) (III) (IV)

Step-by-step solution

The reaction of alcohols with a mixture of NaBr and H ₂ SO ₄ generates HBr , which acts as the reagent for the nucleophilic substitution of the - OH group by - Br . Since the substrates are benzylic alcohols, the reaction proceeds primarily via an S_N1 mechanism. The rate-determining step is the formation of a benzylic carbocation intermediate after the protonation of the alcohol and subsequent loss of a water molecule. The reactivity of the alcohols is directly proportional to the stability of the intermediate car