Which alkyl halide from the following pairs would you expect to react more rapidly by an `S_(N)2` mechanism? Explain your answer.
(ii) `CH_(3)CH_(2)underset(Br)underset(|)(C)HCH_(3) or H_(3)C-underset(CH_(3))underset(|)overset(CH_3)overset(|)(C)-Br`.

Explanation

Out of the two isomeric alkyl bromides, the `alpha` -carbon of `2^(@)` alkyl bromide is less hindered and more positively ploarised. Since, overall electron than the overall effect of one ethyl and methyl group, 2-bromobutance reacts more rapidly by `S_(N)2` mechanism.