CBSE Class 12-science Answered

The S_N1 reaction is a substitution reaction in organic chemistry. S_N stands for nucleophilic substitution and the 1 represents the fact that the rate-determining step is unimolecular.It involves a carbocation intermediate and is commonly seen in reactions of secondary or tertiary alkyl halides or, under strongly acidic conditions, with secondary or tertiary alcohols

S_N2 reaction (also known as bimolecular nucleophilic substitution) is a type of nucleophilic substitution, where a lone pair from a nucleophile attacks an electron deficient electrophilic center and bonds to it, expelling another group called a leaving group. Thus the incoming group replaces the leaving group in one step.