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The mesomeric effect describes how an attached group affects a benzene ring by:
Araising the boiling point of the whole molecule
Bpulling electrons along a chain of sigma bonds
Cphysically blocking the approach of a reagent
Ddonating or withdrawing electrons through the pi system
Answer & Solution
Correct answer: D. donating or withdrawing electrons through the pi system
1. The mesomeric effect concerns delocalised electrons, which live in the pi system.
2. A group attached to a benzene ring can push electrons into that pi system or pull them out of it.
3. That shifts electron density around the ring and so directs where further substitution occurs.
4. Pulling electrons along sigma bonds is the inductive effect instead, and it falls off with distance.
5. A negative inductive effect is that sigma-bond withdrawal by an electronegative group, which is a separate idea from mesomerism.
_Source: NECTA ACSEE 2024 Chemistry 132/1, Question 1: Aliphatic Hydrocarbons_
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