What is mesomeric effect? +M and -M?

What is mesomeric effect?
+M and -M?


3 Answers

Rinkoo Gupta
askIITians Faculty 81 Points
9 years ago
What is a mesomeric effect?"Mesomeric effect" is just a synonym for "resonance effect". If electron density at a particular point in a molecule is higher or lower than what you'd expect from a single Lewis structure, and various canonical structures can be drawn to show how electron delocalization will explain the discrepancy, the difference in electron density is called a "mesomeric effect"
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Rinkoo Gupta
AskIITians Faculty
277 Points
9 years ago
So practically there is no difference in mesomeric effect and resonance?
47 Points
9 years ago
Mesomeric effect or Resonance effect is defined as the ‘polarity produced in the molecule by the interaction of two p-bonds or between a p-bond and lone pair of electrons present on an adjacent atom’. It is designated as R or M effect. Now, a resonance effect can be either positive or negative. Look below positive and negative resonance effects one by one.

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