Question

How are methyl groups electron donating to the phenyl ring? Give a detailed explanation.

Answer 1

Reasons for electron donating nature of methyl group:

1)
Commonly written as Ar-CH3 (Ar-any phenyl ring) is electron donating because of high magnitude of electron cloud  being collected over carbon.
Since carbon is less electronegitive, it do not possess the required nuclear attraction to hold electrons.

2)
They activate the aromatic ring by increasing the electrondensity on the ring through an inductive donatingeffect.
This is the same effect that allows alkyl groups to stabilise simple carbocations.

3)
The electrons in the three C-H bonds of the methyl are drown towards the carbon atom, which causes the fourth valence electron (in the 2px orbital) of the carbon atom to be pushed further away from the nucleus (thus it is at a higher energy level) due to extra repulsion from the C-H electrons.

If this fourth electron is part of a covalent bond (shared pair of electrons) with another atom, y, then the electrons in the C-y bond will be pushed further towards the y atom (again due to the extra repulsion from the three pairs of bonding electrons) making it more delta negative.

Hence, the CH3 group is said to be electron donating.