what are mesomers?explain briefly with one example?

mesomers are a type of compounds in which net rotation of plane polarised light is zero .  i.e to be simple , mesomers are type of organic compounds where two chiral carbons are present and those two are similar , so net rotation is zero . 

 

   

MESOMER IS ONE TYPE OF STEREO ISOMER A COMPOUND HAVING TWO CHIRAL CENTERS DIVIDE THE THE TWO PARTS IF TWO PARTS ARE EQUAL THEN COMPOUND HAVING MESOCOMPOUND

dear jyothi,

                sterioisomers which are achiral instead of chiral r called as the mesomers

  ….….….alll d best!@

dear iitian............

           Stereoisomers which are achiral inspite of having chiral centres are called mesomers….….….….….….….….….….….….….….….….….….…..

Actually , you messed up a with the differents isomers, no one provided similar answers..

 

The terms "mesomerism" or"resonance “ are both used for the model describing the displacement of electrons or protons (used in diffeaction) in a molecule (π ("pi")electrons of π bonds, lone pairs, and electric charges) which stabilize this molecule.
Mesomerism is an Imaginary model; 2 resonances structures  drawn on paper are not isolables physically because they really don't exist! What exist is the resonance hybrid (the molecule which is the hybrid of those 2 , or more, structures). 

 

By convention we use a simple double arrow head between mesomers in Lewis representation.

 

There is several exemples like :
1) conjugaison between 2 pairs of π electrons 
( buta-1,3-diene)
2)conjugaison between pairs of π electrons and lone pairs
(phenol)
3) conjugaison between a pair of π electrons and an "empty case"
(nitrobenzene)
4) conjugaison between a lone pair and an "empty case"

 

Beware! Often people confound tautomerism and mesomerism, but the former is a constitutional isomer , a real chemical reaction occurs ( in many case result in relocation of a proton-and studied with diffraction) so for two tautomers, there are two isolable forms experimentally with ,of course different properties; also here you use two supperposed arrow with the upper pointing right and the other pointing left.

 

Still, keep in mind that orbitals(AO/MO) , bonds , charges,particles or waves are presented in a classical view that don't describe the quantum realm in the best way, but are useful simplifications taught at school

 

Ps: I couldn’t insert a picture to illustrate my exemples but I think there are plenty elsewhere

Mesomers are compounds that have chiral centres ( more than one ), and also have a plane of symmetry. They are optically inactive. Thus they do not rotate plane polarized light. The effect on plane polarized light due to the various chiral centres cancel out making the compound optically inactive. 

This phenomenon is called internal compensation.

 

hope this helped