10.14: Additional Problems

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10 • Additional Problems 10 • Additional Problems

Visualizing Chemistry

Give IUPAC names for the following alkyl halides (green = Cl): (a)

the= (b)

The ball and stick model of an alkyl halide that comprises a seven-carbon chain and one double bond. Black, gray, and green spheres represent carbon, hydrogen, and chlorine, respectively.

(b)

Problem 10-16

The following alkyl bromide can be prepared by reaction of the alcohol (S)-2-pentanol with PBr₃. Name the compound, assign (R) or (S) stereochemistry, and tell whether the reaction of the alcohol results in the same stereochemistry or a change in stereochemistry (reddish brown = Br).

Mechanism Problems

In light of the fact that tertiary alkyl halides undergo spontaneous dissociation to yield a carbocation plus halide ion (see Problem 10-41), propose a mechanism for the following reaction.

Naming Alkyl Halides

(b)
(c)
(d)
(e)

Problem 10-19
Draw structures corresponding to the following IUPAC names: (a)

2,3-Dichloro-4-methylhexane

(b) 4-Bromo-4-ethyl-2-methylhexane (c) 3-Iodo-2,2,4,4-tetramethylpentane (d) cis-1-Bromo-2-ethylcyclopentane

2-methylbutane

(b) methylcyclopropane (c) 2,2-dimethylpentane

Synthesizing Alkyl Halides

Chlorocyclopentane
(b) Methylcyclopentane (c) 3-Bromocyclopentene (d) Cyclopentanol (e) Cyclopentylcyclopentane (f) 1,3-Cyclopentadiene
(b)
(c)
(d)
(e)
(f)
(g)

A chemist requires a large amount of 1-bromo-2-pentene as starting material for a synthesis and decides to carry out an NBS allylic bromination reaction. What is wrong with the following synthesis plan? What side products would form in addition to the desired product?

What product(s) would you expect from the reaction of 1-methylcyclohexene with NBS? Would you use this reaction as part of a synthesis?

What product(s) would you expect from the reaction of 1,4-hexadiene with NBS? What is the structure of the most stable radical intermediate?

What product would you expect from the reaction of 1-phenyl-2-butene with NBS? Explain.

Oxidation and Reduction

(b)

Problem 10-28

Which of the following compounds have the same oxidation level, and which have different levels?

(b)
(c)

General Problems

Problem 10-30
Arrange the following radicals from most stable to least stable. (a)
(b)
(c)

Problem 10-31

Alkylbenzenes such as toluene (methylbenzene) react with NBS to give products in which bromine substitution has occurred at the position next to the aromatic ring (the benzylic position). Explain, based on the bond dissociation energies in Table 6.3.

Draw resonance structures for the benzyl radical, C₆H₅CH₂·, the intermediate produced in the NBS bromination reaction of toluene (Problem 10-31).

(b)
(c)

Problem 10-34

(S)-3-Methylhexane undergoes radical bromination to yield optically inactive 3-bromo-3-methylhexane as the major product. Is the product chiral? What conclusions can you draw about the radical intermediate?

Assume that you have carried out a radical chlorination reaction on (R)-2-chloropentane and have isolated (in low yield) 2,4-dichloropentane. How many stereoisomers of the product are formed, and in what ratio? Are any of the isomers optically active? (See Problem 10-34.)

How would you carry out the following syntheses?

(b)
(c)

Problem 10-38

Why do you suppose it’s not possible to prepare a Grignard reagent from a bromo alcohol such as 4-bromo-1-pentanol? Give another example of a molecule that is unlikely to form a Grignard reagent.

Addition of HBr to a double bond with an ether (−OR) substituent occurs regiospecifically to give a product in which the −Br and −OR are bonded to the same carbon. Draw the two possible carbocation intermediates in this electrophilic addition reaction, and explain using resonance why the observed product is formed.

Identify the reagents a–c in the following scheme:

Tertiary alkyl halides, R₃CX, undergo spontaneous dissociation to yield a carbocation, R₃C⁺, plus halide ion. Which do you think reacts faster, (CH₃)₃CBr or H₂C $\text{=$ ₃)₂Br? Explain.

Carboxylic acids (RCO₂H; pK_a ≈ 5) are approximately 10¹¹ times more acidic than alcohols (ROH; pK_a ≈ 16). In other words, a carboxylate ion (RCO₂⁻) is more stable than an alkoxide ion (RO⁻). Explain, using resonance.

(b)
(c)

Problem 10-44
The relative rate of radical bromination is 1 : 82 : 1640 for 1° : 2° : 3° hydrogens, respectively. Draw all of the monobrominated products that you might obtain from the radical bromination of the compounds below. Calculate the relative percentage of each. (a)
methylcyclobutane
(b) 3,3-dimethylpentane (c) 3-methylpentane
Problem 10-45
Choose the alcohol from each pair below that would react faster with HX to form the corresponding alkyl halide. (a)
(b)
(c)

Problem 10-46
Predict the product and provide the entire catalytic cycle for the following Suzuki–Miyaura reactions. (a)
(b)

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(b)
(c)
(d)
(e)
(f)
(g)

A chemist requires a large amount of 1-bromo-2-pentene as starting material for a synthesis and decides to carry out an NBS allylic bromination reaction. What is wrong with the following synthesis plan? What side products would form in addition to the desired product?

(b)

Problem 10-28

(b)
(c)

General Problems

Problem 10-30
Arrange the following radicals from most stable to least stable. (a)
(b)
(c)

Problem 10-31

(b)
(c)

Problem 10-34

(b)
(c)

Problem 10-38

(b)
(c)

Problem 10-44
The relative rate of radical bromination is 1 : 82 : 1640 for 1° : 2° : 3° hydrogens, respectively. Draw all of the monobrominated products that you might obtain from the radical bromination of the compounds below. Calculate the relative percentage of each. (a)

(b) (c) (d) (e) Problem 10-19 Draw structures corresponding to the following IUPAC names: (a)

(b) (c) (d) (e) (f) (g) A chemist requires a large amount of 1-bromo-2-pentene as starting material for a synthesis and decides to carry out an NBS allylic bromination reaction. What is wrong with the following synthesis plan? What side products would form in addition to the desired product?

(b) Problem 10-28

(b) (c) General Problems Problem 10-30 Arrange the following radicals from most stable to least stable. (a) (b) (c) Problem 10-31

(b) (c) Problem 10-34

(b) (c) Problem 10-38

(b) (c) Problem 10-44 The relative rate of radical bromination is 1 : 82 : 1640 for 1° : 2° : 3° hydrogens, respectively. Draw all of the monobrominated products that you might obtain from the radical bromination of the compounds below. Calculate the relative percentage of each. (a)