Question

CH3 (4) 1. Which of the following alkyl halides would you expect to be most reactive in a unimolecular reaction? a) C&H, CH, CH, CH, BY b) CH 1 CH CH Br C) CH11CCH, Br d) C6H CH2 CH CHỊ CHỊ CH3 CHỊ e) C&H, CCH Br CHE (4) 2. What would you expect to be the chief organic product(s) when tert-butyl bromide reacts with sodium acetylide, i.e., CH3 + - CH2-C-Br + Na :CECH — ? CH a) I b) II c) III d) IV e) None of these (4) 3. Your task is to convert 2-chloropentane into 1-pentene. Which reagents would you choose? a) NaOH/H20 b) KOH/CH3OH c) CH3ONa/CH3OH d) CH3CH2ON/CH3CH2OH e) (CH3)3COK/(CH3)3COH (4) 4. Which alkyl halide would you expect to react more rapidly by an Sy2 mechanism? a) CH2CH2CH2CH_Br or CH2CH2 CHCH3 Br CH2 CH2 CH CH, Br b) CH3 CH CH, CH,Bror CHE CH3

Answer 1

1.

Correct option: d

Option e can be immediately ruled out as it is not an alkyl halide but an alkane.

Alkyl halides in options a to c are primary alkyl halides. Primary alkyl halides are known to undergo bimolecular reactions (e.g. S_N2 and E2) as they give the least stable carbocations.

The alkyl halide in option d is secondary. Hence, it can give a relatively stable secondary carbocation. Thus, the alkyl halide d can form products via E1 and S_N1 mechanism. In S_N1 and E1, the rate of the reaction only depends on the alkyl halide. Therefore, the alkyl halide d is expected to be most reactive in a unimolecular reaction.