Organic chemistry

Mesomeric Effect – Definition,Types,Order and Uses

Mesomeric Effect – Definition, Types, Order, and Uses

It is an important topic in organic chemistry like the inductive effect. You must know about the mesomeric effect, so that helps a lot in learning reaction mechanisms in organic chemistry

Mesomeric Effects (or) Resonance Effect:-




       Whilst inductive Effect pulls electrons through the Sigma Bond framework, electrons can also move through the π- bond network. The π-bond can stabilize a negative charge, a positive charge, a lone pair of electrons, or an adjacent bond by Resonance ( i.e. Delocalisation (or) “Spreading out”  of the electrons ).

What are the types of Mesomeric effect ?? (Or) What is meant by +M,-M effects ??

Okay, let’s See for the answers

The Mesomeric effect is divided into two different types:-
1. Positive Mesomeric Effect
2. Negative Mesomeric Effect
Curly Arrows are used to represent the movement of π- electron (or) Non-bonding electrons to give different resonance forms. It is only the electrons, not the nuclei, that move in the resonance forms, and a double-headed arrow is used to show their relationship.


* When a π-system donates electrons, the π-system has a positive Mesomeric effect (+ M – Effect)
The Lone pair of the Hetroatoms can alos be in the part of the Resonance effect if it is present in particular compound



When a π- system accepts electrons, the π- system has a negative mesomeric effect ( – M Effect ).


• The Actual Structures of cations or anions lie somewhere between the two resonance formsMesomeric effect , mesomeric effect vs inductive effect , explain mesomeric effect , mesomerice effect vs resonance effect, importance of Mesomeric effect, effects in organic chemistry, general organic chemistry, mesomeric effect Explained,
Some of the Positive & Negative Mesomeric group are listed below:-



Left Side:  Negative Mesomeric Groups
Right Side: Positive Mesomeric Groups
Credits: Advanced Organic Chemistry By Arun Bahl | B.S Bahl
What is the Order of Mesomeric Effecting Groups ??
The Order of Mesomeric Effect Produced By the Groups Are:-
Order of +M effect &

Order of -M effect:-

Order of Mesomeric Effecting Groups, crackchemistry
Order of Mesomeric Effecting Groups

+ R mentioned in the above image denotes the +M effect.

-R mentioned in the above image denotes the – M effect.

Questions Asked from these parts:-

Stability of Double Bonded Carbocation/Carbanions
Acidity & Basicity
• Resonance Stability of Cyclic (or) Aromatic Compounds
• Stability Of Oxides, Nitrides, etc..,
To see about Mesomeric Effect in Wikipedia – Click here
In this article,you have learned about the Mesomeric Effect – Definition, Types, Order, and Uses
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