← Back

Chapter 11: Reactions of Alkyl Halides: Nucleophilic Substitutions and Eliminations

Every problem in the chapter beside the book’s answer, a chapter at a time as you scroll.

Chapter 11: Reactions of Alkyl Halides: Nucleophilic Substitutions and Eliminations

20 problems · 21 figures

11-1 §11.1 source ↗

What product would you expect from a nucleophilic substitution reaction of (S)-2-bromohexane with acetate ion, CH3CO2–? Assume that inversion of configuration occurs, and show the stereochemistry of both the reactant and product.

Answer

(R)-1-Methylpentyl acetate, CH3CO2CH(CH3)CH2CH2CH2CH3

11-2 §11.2 source ↗

What product would you expect to obtain from SN2 reaction of OH– with (R)-2-bromobutane? Show the stereochemistry of both the reactant and product.

Answer

(S)-2-Butanol

11-3 §11.2 source ↗

Assign configuration to the following substance, and draw the structure of the product that would result from nucleophilic substitution reaction with HS– (reddish brown = Br):

Answer

11-4 §11.3 source ↗

What product would you expect from SN2 reaction of 1-bromobutane with each of the following?
(a)
NaI
(b)
KOH
(c)
H−C ≡ C−Li
(d)
NH3

Answer (4 parts)

(a)
1-Iodobutane
(b)
1-Butanol
(c)
1-Hexyne
(d)
Butylammonium bromide

11-5 §11.3 source ↗

Which substance in each of the following pairs is more reactive as a nucleophile? Explain.
(a)
(CH3)2N– or (CH3)2NH
(b)
(CH3)3B or (CH3)3N
(c)
H2O or H2S

Answer (3 parts)

(a)
(CH3)2N−
(b)
(CH3)3N
(c)
H2S

11-6 §11.3 source ↗

Rank the following compounds in order of their expected reactivity toward SN2 reaction:

CH3Br, CH3OTos, (CH3)3CCl, (CH3)2CHCl

Answer

CH3OTos > CH3Br > (CH3)2CHCl > (CH3)3CCl

11-7 §11.3 source ↗

Organic solvents like benzene, ether, and chloroform are neither protic nor strongly polar. What effect would you expect these solvents to have on the reactivity of a nucleophile in SN2 reactions?

Answer

Similar to protic solvents

11-8 §11.4 source ↗

What product(s) would you expect from reaction of (S)-3-chloro-3-methyloctane with acetic acid? Show the stereochemistry of both reactant and product.

Answer

Racemic 1-ethyl-1-methylhexyl acetate

11-9 §11.4 source ↗

Among the many examples of SN1 reactions that occur with incomplete racemization, the optically pure tosylate of 2,2-dimethyl-1-phenyl-1-propanol ([α]D = –30.3) gives the corresponding acetate ([α]D = +5.3) when heated in acetic acid. If complete inversion had occurred, the optically pure acetate would have had [α]D = +53.6. What percentage racemization and what percentage inversion occurred in this reaction?

Answer

90.1% racemization, 9.9% inversion

11-10 §11.4 source ↗

Assign configuration to the following substrate, and show the stereochemistry and identity of the product you would obtain by SN1 reaction with water (reddish brown = Br):

Answer

11-11 §11.5 source ↗

Rank the following substances in order of their expected SN1 reactivity:

Answer

H2C ═ CHCH(Br)CH3 > CH3CH(Br)CH3 > CH3CH2Br > H2C ═ CHBr

11-12 §11.5 source ↗

3-Bromo-1-butene and 1-bromo-2-butene undergo SN1 reaction at nearly the same rate, even though one is a secondary halide and the other is primary. Explain.

Answer

The same allylic carbocation intermediate is formed.

11-13 §11.5 source ↗

Predict whether each of the following substitution reactions is likely to be SN1 or SN2:
(a)
(b)

Answer (2 parts)

(a)
SN1
(b)
SN2

11-14 §11.6 source ↗

Review the mechanism of geraniol biosynthesis shown in Figure 11.16, and propose a mechanism for the biosynthesis of limonene from linalyl diphosphate.
Figure 11.16 in the book ↗
Biosynthesis of geraniol from dimethylallyl diphosphate. Two SN1 reactions occur, both with diphosphate ion as the leaving group.

Answer

11-15 §11.7 source ↗

Ignoring double-bond stereochemistry, what products would you expect from elimination reactions of the following alkyl halides? Which product will be the major product in each case?
(a)
(b)
(c)

Answer (3 parts)

(a)
Major: 2-methyl-2-pentene; minor: 4-methyl-2-pentene
(b)
Major: 2,3,5-trimethyl-2-hexene; minor: 2,3,5-trimethyl-3-hexene and 2-isopropyl-4-methyl-1-pentene
(c)
Major: ethylidenecyclohexane; minor: cyclohexylethylene

11-16 §11.7 source ↗

What alkyl halides might the following alkenes have been made from?
(a)
(b)

Answer (2 parts)

(a)
1-Bromo-3,6-dimethylheptane
(b)
4-Bromo-1,2-dimethylcyclopentane

11-17 §11.8 source ↗

What stereochemistry do you expect for the alkene obtained by E2 elimination of (1R,2R)-1,2-dibromo-1,2-diphenylethane? Draw a Newman projection of the reacting conformation.

Answer

(Z)-1-Bromo-1,2-diphenylethylene

11-18 §11.8 source ↗

What stereochemistry do you expect for the trisubstituted alkene obtained by E2 elimination of the following alkyl halide on treatment with KOH? (reddish brown = Br.)

Answer

(Z)-3-Methyl-2-pentene

11-19 §11.9 source ↗

Which isomer would you expect to undergo E2 elimination faster, trans-1-bromo-4-tert-butylcyclohexane or cis-1-bromo-4-tert-butylcyclohexane? Draw each molecule in its more stable chair conformation, and explain your answer.

Answer

Cis isomer reacts faster because the bromine is axial.

11-20 §11.12 source ↗

Tell whether each of the following reactions is likely to be SN1, SN2, E1, E1cB, or E2:
(a)
(b)
(c)
(d)

Answer (4 parts)

(a)
SN2
(b)
E2
(c)
SN1
(d)
E1cB

Loading chapter 12…

Problems and answers are adapted from Organic Chemistry: A Tenth Edition by John McMurry, OpenStax, and are used under the CC BY-NC-SA 4.0 licence. Access for free at https://openstax.org/books/organic-chemistry/pages/1-why-this-chapter. Illustrations: Copyright Rice University, OpenStax, under CC BY-NC-SA 4.0 license. This adaptation is released under the same licence, is non-commercial, and is neither affiliated with nor endorsed by OpenStax or Rice University.