Choose the alkyl halide(s) (a, b, c, d, or e) from the following list of C_6H_13
ID: 1009530 • Letter: C
Question
Choose the alkyl halide(s) (a, b, c, d, or e) from the following list of C_6H_13Br isomers that meet each criterion below: give brief reasons for your answer 1-bromohexane 3-bromo-3-methylpentane 1-bromo-2,2-dimethylbutane 3-bromo-2-methylpentane 2-bromo-3-methylpentane the compound that gives the fastest S_N^2 reaction with methanol ii. the compound that is incapable of reacting with sodium methoxide in methanol iii. the compound that gives an E2 reaction but not an S_N^2 reaction with sodium methoxide in methanol iv. the compound that gives an S_N^1 reaction with rearrangement v. the compound that gives only one alkene in the E2 reactionExplanation / Answer
4) We look at the structural formula for the given compounds and try to match them with the given molecular formula, C6H13Br.
(i) Primary halides gives the fastest SN2 reaction; also the lower the branching, the back-side attack by the nucleophile is preferred. Hence, (a) 1-bromohexane will give the fastest SN2 reaction.
(ii) (c) 1-bromo-2,2-dimethylbutane will not react with sodium methoxide in methanol because there are no hydrogen atoms on the carbon adjacent to the C-Br group to give the elimination product.
(iii) (d) 3-bromo-2-methylpentane undergoes ready E2 reaction (since more substituted alkyl halide) with sodium methoxide in methanol. This compound doesn’t undergo SN2 reaction as it has a higher tendency to form a tertiary carbocation on reaction with methoxide.
(iv) (e) 2-bromo-3methylpentane gives an SN1 product with rearrangement. A secondary carbocation is initially formed which rearranges to a more stable tertiary carbocation to give the substitution product.
(v) (b) 3-bromo-3-methylpentane gives only one alkene on elimination since it is a symmetrical alkyl halide.