Question

Which of the following group show -M effect?

• A. -CMe$_3$
• B. -O-SO₂-OR
• C. -NH-C(=O)-CH₃
• D. -SO₂-OR

Answer 1

Answer: (D)

D

Answer 2

-M effect is shown by groups that withdraw electrons from a conjugated system via resonance. This typically occurs when the atom directly attached to the conjugated system is part of a multiple bond with a more electronegative atom, or has vacant d-orbitals to accept electrons.

(A) -CMe₃ is an alkyl group, showing +I effect.

(B) -O-SO₂-OR is attached via oxygen, which has lone pairs, thus showing +M effect.

(C) -NH-C(=O)-CH₃ is attached via nitrogen, which has a lone pair, thus showing +M effect.

(D) -SO₂-OR is attached via sulfur, which is double-bonded to electronegative oxygen atoms and has empty d-orbitals. It can accept electrons from the conjugated system, hence showing a -M effect.