Question -
Answer -
Explain your answer.
Answer
(i)
2-bromobutane is a 2° alkylhalide whereas1-bromobutane is a 1° alkyl halide. The approaching of nucleophile is morehindered in 2-bromobutane than in 1-bromobutane. Therefore, 1-bromobutanereacts more rapidly than 2-bromobutane by an SN2mechanism.
(ii)
2-Bromobutane is 2° alkylhalide whereas2-bromo-2-methylpropane is 3° alkyl halide. Therefore, greater numbers ofsubstituents are present in 3° alkyl halide than in 2° alkyl halide to hinderthe approaching nucleophile. Hence, 2-bromobutane reacts more rapidly than2-bromo-2-methylpropane by an SN2 mechanism.
(iii)
Both the alkyl halides are primary. However,the substituent −CH3 is at a greater distance to the carbon atom linkedto Br in 1-bromo-3-methylbutane than in 1-bromo-2-methylbutane. Therefore, theapproaching nucleophile is less hindered in case of the former than in case ofthe latter. Hence, the former reacts faster than the latter by SN2mechanism.