91Ó°ÊÓ

In some compounds, when a charge and pi bond is present on adjacent carbon, delocalization of the electrons occurs.

It increases the stability of charges in a compound and the more the number of resonance structures; the more is the stability of the compound.

Resonance structures are represented by Lewis structures.

The resonance structures are called canonical structures and are formed by to delocalization of pi bonds or lone pairs.

The actual structure will be a hybrid of all resonance structures possible for the compound.

(a) The lone pair on the chlorine atom is delocalized between the chlorine atom and the carbon-chlorine bond giving the carbon-chlorine bond a partial double bond character.

Canonical structures of (a)

(b) The pi electrons resonate between the three bonds giving all the three bonds a double bond character.

Canonical structures of (b)

(c) The lone pair on nitrogen and pi electrons take part in resonance to give three canonical structures.

Canonical structures of (c).