Write a note on nucleophillc substitution reactions.

Explanation

A reaction in which a nucleophile replaces already existing nucleophile in a molecule is called nucleophilic substitution reactions.
In these reactions, haloalkanes are substrate and the nucleophile reacts with a substrate having a partial positive charge on the carbon atom bonded to halogen atom. A substitution reaction takes place and halogen atom, called a leaving group departs as halide ion. Since the substitution reaction is initiated by a nucleophile, it is called nucleophilic substitution reaction `(S_(N))`.

The nucleophilic substitution reactions are of two types : (i) Unimolecular Nucleophilic Substitution reaction `(S_(N)1)`. (ii) Bimolecular Nucleophilic Substitution reaction `(S_(N)2)`.
Nucleophilic Substitution of Alkyl Halides (R - X)
General Reaction : `R-X+Nu^(-)to R-Nu+X^(-)`