91Ó°ÊÓ

An electron-deficient species is known as an electrophile. This chemical entity accepts electrons and is thus a Lewis acid.

For example, a carbon attached to a more electronegative hetero-atom is an electrophilic center.

The species having an excess of electrons are called nucleophiles. These species are called Lewis bases because they tend to donate an electron pair.

For example, all hetero atoms having lone pairs of electrons or species having at least one $\mathrm{Ï€}-\mathrm{bond}$ form a nucleophilic center.

a.

The given compound consists of an electronegative heteroatom, i.e., bromine. Hence, the carbon attached to bromine is electrophilic, while bromine itself is nucleophilic.

Electrophilic and nucleophilic sites in a.

b.

The compound consists of an electronegative atom, i.e., sulfur, and $\mathrm{Ï€}-\mathrm{bond}$both of which form nucleophilic sites. The carbon atoms attached to the hetero atom sulfur form an electrophilic site.

Electrophilic and nucleophilic sites in b.

c.

The compound consists of two electronegative atoms at three sites and a $\mathrm{Ï€}-\mathrm{bond}$; all of them form nucleophilic sites. The carbon atoms directly bonded to these atoms form electrophilic sites.

Electrophilic and nucleophilic sites in c.