Question

Phenol has a smaller dipole moment than methanol.Give reason.

Answer 1

the -OH group in phenol has -I effect as well as +R effect. Due to the - I effect electrons are drawn towards the -OH group of phenol and due to +R effect electron or lone pair on oxygen atom are delocalize over the ring or in other word electron density is pushes away from the -OH group of phenol. Therefore the bond moments is in opposite direction. As a result the two oppositely acting bond moments nearly cancel each other and hence has very smaller dipole moment.
Whereas in case of methanol due to the +R effect of methyl group the electron are pushes towards the -OH group.In addition to this electronegativity of oxygen is more than that of methyl carbon, which also pulls electron density towards itself(- towards -OH group). No such opposing bond moments are there in methanol,therefore the bond moments is totally towards the -OH group and hence shows considerable and greater dipole moment than in phenol.

Answer 2

Hey !!

In Phenol C ---- O bond is less polar due to electron - withdrawing effect of benzene ring whereas in methanol C ---- O bond is more polar due to electron - releasing effect of ----CH₃ group.

Good luck !!