question_answer

  Explain (i) Why is orthonitrophenol more acidic than orthomethoxy phenol? (ii) How does the ?OH group attached to a carbon of benzene ring activate it towards electrophonic substitution?                                                                                                                                                                                               [1+1]

Answer:

  (i) ? group is electron-withdrawing group and thus, stability of nitrophenoxide is further increased. - group is electron-repelling group which decreases stability of methoxy peroxide ion. Thus, o-nitro phenol  is more acidic than o-methoxyphenol.                                         [1] Due to resonance electron-density at o ? and p-positions is increased. Resonance hybrid of the above structures is given below Electrophile can attack at these sites which are o- and p- wrt to ?OH group. Thus, ?OH group activates benzene nucleus for o- and p-attack.                                         [1]