How would you differentiate betweenS_(N)1 " and " S_(N)2 mechanisms of substitution reactions ? Give one example of each.

How would you differentiate betweenS_(N)1 " and " S_(N)2 mechanisms of

1.	How would you differentiate betweenS_(N)1 " and " S_(N)2 mechanisms of substitution reactions ? Give one example of each.
Answer» Solution :There are TWO different ways in which the substitution reactions of alkyl halides take place. (a) Substitution nucleophilic unimolecular `S_(N)1` : The reaction between tert. butyl chloride and hydroxide ion yields tert-butyl hydroxide and follows first order kinetics `(S_(N)1)` i.e., rate of the reaction depends upon one concentration terms i.e. tert. butyl chloride. The reaction occurs in two steps: `(CH_(3))_(3)C Cl to (CH_(3))_(3)C^(+) + Cl^(-) ` (First step ) Slop step `(CH_(3))_(3)C Cl + OH^(-) to (CH_(3))_(3)COH ` Fast step (b)Substitution nucleophilic bimolecular `S_(N)2` : The reaction between `CH_(3)Cl`and hydroxide ion to yield METHANOL and chloride ion follows a second order kinetics i.e., the rate of reaction depends upon the concentration of both terms. `CH_(3)Cl + OH^(-) overset(S_(N)2) to underset("Intermediate")([HO * * * * CH_(3)* * * * Cl^(-)]^(-)) to CH_(3)OH + CL^(-)` In the first step, `CH_(3)Cl " and " OH^(-)`react to FORM the intermediate compound. This is the slow step. In the second step, which is fast, the intermediate decomposes to yield the PRODUCTS.