Question

Classify each substituent as electron donating or electron withdrawing.

Short answer

a. Electron donating substituents.

b. Electron withdrawing substituents.

c. Electron donating substituents.

Step-by-step solution

Substituents

The substituents (placed on the ring) can have an electron attracting tendency or electron-donating tendency. The nature of the substituents depends upon the atoms present in the substituents.

Electron donating and electron-withdrawing groups

• The electron-withdrawing substituents have an electronegative atom that attracts electrons towards themselves. Therefore, the positive charge delocalizes on the ring.

• The electron-donating substituents have an electropositive atom which gives electrons to the ring. Therefore, the negative charge delocalizes on the ring.

Explanation

a. The ${\text{CH}}_{\text{3}}\text{O}$ group is an electron-withdrawing substituent but the oxygen has lone pair of electrons which is donated to the ring. Therefore, here ${\text{CH}}_{\text{3}}\text{O}$group is an electron-donating substituent.

b. The iodine group is an electron-withdrawing substituent because iodine is an electronegative atom.

c. The ${\left({\text{CH}}_{\text{3}}\right)}_3{\text{C}}^{-}$group is an electron-donating substituent because carbon is an electropositive atom.