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Chapter 14: Problem 305

Which compound of each of the following sets would you expect to give the higher yield of substitution product under conditions for bimolecular reaction? (a) ethyl bromide or \(\beta\) -phenylethy 1 bromide; (b) \(\alpha\) -phenylethy 1 bromide or \(\beta\) -phenylethyl bromide; (c) isobutyl bromide or \(\mathrm{n}\) -butyl bromide; (d) isobuty1 bromide or tert-buty1 bromide.

Short Answer

Expert verified
(a) Ethyl bromide: lesser steric hindrance than β-phenylethyl bromide. (b) β-phenylethyl bromide: lesser steric hindrance than α-phenylethyl bromide. (c) n-butyl bromide: lesser steric hindrance than isobutyl bromide. (d) Isobutyl bromide: lesser steric hindrance than tert-butyl bromide.

Step by step solution

01

(a) Compare ethyl bromide and β-phenylethyl bromide

To determine which compound gives a higher yield of substitution product in an S_N2 reaction, we must consider the steric hindrance around the carbon atom attached to the bromine. Ethyl bromide has a smaller steric hindrance compared to β-phenylethyl bromide due to the phenyl group attached to the β-carbon. Therefore, ethyl bromide is expected to give a higher yield of substitution product in an S_N2 reaction.
02

(b) Compare α-phenylethyl bromide and β-phenylethyl bromide

In α-phenylethyl bromide, the phenyl group is directly attached to the carbon bearing the bromine atom, causing greater steric hindrance. On the other hand, in β-phenylethyl bromide, the phenyl group is attached to the neighboring (β) carbon atom, leading to lesser steric hindrance compared to α-phenylethyl bromide. Thus, we can expect that β-phenylethyl bromide will give a higher yield of substitution product under S_N2 conditions.
03

(c) Compare isobutyl bromide and n-butyl bromide

Both isobutyl bromide and n-butyl bromide contain four carbon atoms, but differ in their structural arrangement. The n-butyl bromide has a linear chain structure, while isobutyl bromide has a branched structure. Linear chains have lesser steric hindrance; therefore, n-butyl bromide would give a higher yield of substitution product under S_N2 conditions compared to isobutyl bromide.
04

(d) Compare isobutyl bromide and tert-butyl bromide

Isobutyl bromide and tert-butyl bromide differ in the degree of substitution at the carbon atom attached to the bromine. The carbon in isobutyl bromide is secondary (two alkyl groups attached), while the carbon in tert-butyl bromide is tertiary (three alkyl groups attached). Tertiary carbons have greater steric hindrance and are less likely to undergo S_N2 reactions. Therefore, we can expect that isobutyl bromide will give a higher yield of substitution product under S_N2 conditions compared to tert-butyl bromide.

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Most popular questions from this chapter

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