a) i) SN1 reaction is a unimolecular nucleophilic substitution reaction. It involves the substitution of a weaker nucleophile by a stronger one and follows first-order kinetics, i.e., the rate of reaction depends upon the concentration of only one reactant. It occurs in two steps. In step I, the polarised C – X bond undergoes slow cleavage to produce a carbocation.
ii) SN1 reaction follows the order 10 alkyl halides < 2° alkyl halides < 3° alkyl halides.
CH3CH2CH2CH2Br < (CH3)2CHCH2Br < CH3CH2CH(Br)CH3 < (CH3)3CBr
b) By Sandmeyer reaction – When freshly prepared benzene diazonium chloride solution is mixed with cuprous chloride the diazonium group is replaced by -Cl to form chlorobenzene.
OR
By Gatterman reaction – When freshly prepared benzene diazonium chloride solution is treated with hydrochloric acid in presence of copper pow- der the diazonium group is replaced by -Cl to form chlorobenzene.