Write a short note on RESONANCE EFFECT.

The polarity produced in the molecule by the interaction of two pi bonds or between a pi bond and loan pair of electron present on an adjacent atom is known as RESONANCE EFFECT. There are two types of resonance effect: 

Positive resonance effect ;  (Transfer of electron is away from an atom or substituent group attached to the conjugated system) +R effect e.g. –OH, -OR, -NH₂ 

Negative resonance ;          (Transfer of electron is towards the atom or substituent group attached to the conjugated system) –R effect e.g. –COOH, -CHO, -CN 

Resonance Effect: The polarity produced in the molecule by the interaction of two pi bonds or between a pi bond and lone pair of electron present on an adjacent atom.

(i) Positive resonance effect: In this effect, the transfer of electrons is away from an atom or substituent group attached to the conjugated system. The atoms of groups which show + R effect are halogens, -OH, -OR, -NH₂ etc.

(ii) Negative resonance effect: In this effect, the transfer of electrons is towards the atom or substituent group attached to the conjugated system. The atoms or groups which dhow -R effect is -COOH -CHO, -CH etc.