Question -
Answer -
(i) CH_3Br or CH_3I
(ii) (CH_3)_3CCl or CH_3Cl
Answer
(i) In the SN2 mechanism, thereactivity of halides for the same alkyl group increases in the order. Thishappens because as the size increases, the halide ion becomes a better leavinggroup.
R−F << R−Cl < R−Br < R−I
Therefore, CH3Iwill react faster than CH3Br in SN2 reactions with OH−.
(ii)
The SN2 mechanism involvesthe attack of the nucleophile at the atom bearing the leaving group. But, incase of (CH3)3CCl, the attack of the nucleophile at the carbon atom ishindered because of the presence of bulky substituents on that carbon atombearing the leaving group. On the other hand, there are no bulky substituentson the carbon atom bearing the leaving group in CH3Cl.Hence, CH3Cl reacts faster than (CH3)3CClin SN2 reaction with OH−.