The high reactivity of alkyl halides can be explained in terms of nature of C-X bond which is a highly polarised covalent bond. This polarity is responsible for the nucleophilic substitution reaction of alkyl halides which jmostly occur by S_(N^(1)) and S_(N^(2)) mechanisms. S_(N^(1)) reaction is a two step process and in the first step R-X ionises to give carbocation (slow process). IN the second step, the nucleophile attacks the carbocation from either side to form the product (fast process). IN S_(N^(1)) reaction, there can be racemization and inversion. S_(N^(1)) reaction is favoured by heavy (bulky) group on the carbon atom attached to halogens. IN S_(N^(2)) reaction, the strong nucleophile OH^(-) attacks fromt he opposite side Of the halogen atom to give an intermediate (transition state), which breaks to yields to product (alcohol) and leaving group (X^(-)). The alcohol has a configuratio opposite to that of the halide and is said to proceed with inversion of configuration. S_(N^(2)) reaction is favoured by small groups on the carbon atom attached to halogen. Q. Which among the following will not give S_(N^(1)) reaction?

The high reactivity of alkyl halides can be explained in terms of natu

1.	The high reactivity of alkyl halides can be explained in terms of nature of C-X bond which is a highly polarised covalent bond. This polarity is responsible for the nucleophilic substitution reaction of alkyl halides which jmostly occur by S_(N^(1)) and S_(N^(2)) mechanisms. S_(N^(1)) reaction is a two step process and in the first step R-X ionises to give carbocation (slow process). IN the second step, the nucleophile attacks the carbocation from either side to form the product (fast process). IN S_(N^(1)) reaction, there can be racemization and inversion. S_(N^(1)) reaction is favoured by heavy (bulky) group on the carbon atom attached to halogens. IN S_(N^(2)) reaction, the strong nucleophile OH^(-) attacks fromt he opposite side Of the halogen atom to give an intermediate (transition state), which breaks to yields to product (alcohol) and leaving group (X^(-)). The alcohol has a configuratio opposite to that of the halide and is said to proceed with inversion of configuration. S_(N^(2)) reaction is favoured by small groups on the carbon atom attached to halogen. Q. Which among the following will not give S_(N^(1)) reaction?
Answer» `CH_(3)-underset(C_(6)H_(5))underset(\|)(C)H-Br` `(CH_(3))_(3)C-Br` `CH_(3)CH_(2)-I` `(C_(6)H_(5))_(2)underset(CH_(3))underset(\|)(C)-Cl`. SOLUTION :Primary alkyl halides PREFERABLE REACT by `S_(N^(2))` mechanism.