Electromeric effect and mesomeric effect.

What is electromeric effect ?

This  is a temporary effect involving  the complete transfer of a shared pair of electrons to one or other atom  joined by  a multiple bond that is a double or triple bond.

OR

A temporary but complete displacement of electron pair forming a pi bond between two different atoms, toward the more electronegative atom at the requirement of attacking  species is called   electromeric effect, denoted by the symbol’ E ‘. 

There are two types  of electromeric  effect,  +E  effect   and  - E  effect.

What  is difference  between  electromeric  effect   and  inductive  effect ?

A temporary but complete displacement of electron pair forming a pi bond between two different atoms , toward the more electronegative atom at the requirement of attacking  species is called electromeric  effect.

It is a temporary effect.  It  is the polarizability of a multiple bond. In electromeric  effect , pi bond  bonds are involved. Complete transfer of pi electrons  takes  place  in this effect.

Inductive effect  is  permanent  but partial displacement   of electron along the bond in a molecule  actually toward the more electronegative atom due to electronegative difference of the  atom  forming  the  bond .

It  is a permanent  effect . It is  the  permanent  polarization of  a single bond. In  inductive effect,  sigma  electrons  are involved.  Only  electron  displacement  takes place in this  effect.

What  is  mesomeric  effect ?

The  effect  which helps  redistribution of  electrons  with permanent  polarization in the ground state of an entity  in unsaturated and chiefly in conjugated system  via  pi  orbital  is called  mesomeric  effect , denoted  by  ‘M’ .

There are two type  of  mesomeric  effect ,  +M  effect  and  -M   effect .   

When electron  density of a conjugated system increases by  a group through resonance  then this phenomenon of increasing the electron density is called + M effect.

When electron  density of a conjugated system  decreases by  a group through resonance  then this phenomenon of decreasing  the electron density is called  - M effect.

Summary:



What is electromeric effect ? give example.
What is difference between inductive effect and electromeric effect.
What is mesomeric effect ? 

Click here:Inductive effect and field effect.