91Ó°ÊÓ

The chemical reaction in which a functional group replaces another is termed as substitution reaction.

The reactions involving the loss of atoms/groups (breakage of sigma bond) from a compound leading to the formation of a pi bond is referred to as elimination reactions.

The reactions that involve the addition of atoms/groups to a molecule are termed addition reactions.

An addition reaction is generally characterized by the breakage of a pi bond and the formation of two sigma bonds.

a.

Reaction a

In the given reaction the bromine (Br) atom replaces the hydroxyl (OH) group.

Therefore, the given reaction is a substitution reaction.

b.

Reaction b

In the given reaction, two hydrogen atoms are added to the starting material (one hydrogen is added to the oxygen atom and the other to the carbonyl carbon).

Therefore, the given reaction is an addition reaction.

c.

Reaction c

In the given reaction the hydrogen atom of the methyl group is replaced by a chlorine atom and hence the reaction is a substitution reaction.

d.

Reaction d

The given reaction involves the loss of a water molecule (H + OH) and results in the formation of a pi bond.

Therefore, the given reaction is an elimination reaction.