Resonance Effect

Resonance Effect
It is the polarity induced in a pi Bond and lone pair of electron or between two pi bonds.
Resonance effect is defined as decrease in electron density at and position followed by the increase in electron density at another position.
The effect may be positive or negative.
Figure shows the different resonance Structure of different compounds.

Resonance effect  may be positive or negative.

Positive resonance effect:

Atoms which donate Electrons toward carbonshow +M effect.

Electron donating groups:

For example- -OH, -SH, -OR,-SR.

Negative resonance effect:

Atoms which accept electrons or withdraw electrons from other atoms show negative resonance effect.

For example- -NO2, C=O, -COOH, -C≡N.