Question
Explain giving reasons, why:
Phenol has a smaller dipole moment than methanol?
Solution
Phenol has a smaller dipole moment (1.54 D) than methanol. The smaller dipole moment of phenol is due to the electron withdrawing effect of phenyl group (whereas alkyl group in alcohols has electron releasing effect).
In phenol, the lone pairs of electrons of the oxygen atom are delocalised across the aromatic ring (via electron transfer known as resonance) this reduces the polarity of the C-O bond. Methanol, which has no aromatic ring and the lone pair of electrons from the oxygen are not delocalised meaning that the C-O bond, in this case, has a higher polarity.
