question_answer 60)

  Mark the correct increasing order of reactivity of the following compounds with HBr/HCl. (a)                          (b) (c)                          (d)

Answer:

  (c) All the three benzyl alcohols react with HBr/HCl through intermediate formation of carbocations. Obviously more stable the carbocation, more reactive is the alcohol. Now electron-withdrawing groups, i.e.,  Cl, etc. decrease the stability of carbocations. Since the -  group is a stronger electron- withdrawing group than - Cl, therefore, stability of carbocations increases in the order Therefore, reactivity of the benzyl alcohols increases in the same order, i.e., II < III < I. Thus, option (c) is correct.