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.
1.POSITIVE MESOMERIC EFFECT:-
* 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
2.NEGATIVE MESOMERIC EFFECT;-
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 forms
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 |
+ 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..,
• Polarity
To see about Mesomeric Effect in Wikipedia – Click here
Conclusion:-
In this article,you have learned about the Mesomeric Effect – Definition, Types, Order, and Uses
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Originally posted 2022-10-28 06:57:00.