Resonance | Mesomeric Effect | Reaction Mechanism |

  • The phenomenon of delocalization of pi electrons in a conjugated system is called resonance.
  • This delocalization of pi electrons in the molecule decresases the energy of molecule and increases the stability of molecules.
  • The decrease in the energy i.e potential energy due to decolazation of pi electrons is known as resonance or also know as mesomeric effect.
  • In resonance the molecule can be represented by more than one structure called as resonating structure which increases the stability.
  • There are different structute , they are called resonating structure or canonical structure or contributing structures.

There are the followings conditions for resonance :

  • Shifting of pi electrons occurs.
  • nuclei remains same in all structures.
  • charged structures are less stable than uncharged.
  • energy content will be almost same.
  • more the number of resonating structure more will be the stability.

Difference between Resonance and Mesomeric effect

  • Resonance involves all types of electron displacements.
  • While the mesomeric effect noticable only in those cases where a multiple bond is in conjugated with a multiple bond or electron pair.

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