Organic Chemistry

Paula Yurkanis Bruice

Chapter 12 Radicals - all with Video Answers

Educators

Chapter Questions

02:23

Problem 1

Write the initiation, propagation, and termination steps for the monochlorination of cyclohexane.

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03:52

Problem 2

Write the steps for formation of tetrachloromethane (CCl, ) from the reaction of methane with $\mathrm{Cl}_{2}+h \nu$.

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01:05

Problem 3

a. Which of the hydrogens in the structure in the margin is the easiest for a chlorine radical to remove?
b. How many secondary hydrogens does the structure have?

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03:01

Problem 4

How many alkyl chlorides are obtained from monochlorination of the following alkanes? Disregard stereoisomers.

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01:23

Problem 5

If cyclopentane reacts with more than one equivalent of $\mathrm{Cl}_{2}$ at a high temperature, how many dichlorocyclopentanes would you expect to obtain as products?

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07:30

Problem 6

How many alkyl halides are obtained from monochlorination of the alkanes in Problem 4 if stereoisomers are included?

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03:40

a. What is the major monobromination product of the following reaction? Disregard stereoisomers.
b. What is the anticipated percent yield of the major product (as a percentage of all the monobrominated products)?

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03:09

Problem 8

a. What is the major product of the reaction in Problem 7 when the alkane reacts with $\mathrm{Cl}_{2}$ instead of with $\mathrm{Br}_{2}$ ? Disregard stereoisomers.
b. What is the anticipated percent yield of the major product?

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02:51

Problem 9

a. Would chlorination or bromination produce a greater yield of 1-halo-2,3-dimethylbutane?
b. Would chlorination or bromination produce a greater yield of 2-halo-2,3-dimethylbutane?
c. Would chlorination or bromination be a better way to make 1-halo-2,2-dimethylpropane?

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01:21

Problem 10

How could butanone be prepared from butane?

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02:15

Problem 11

Show how the following compounds could be prepared from 2 -methylpropane:
a. 2 -bromo- 2 -methylpropane
b. 2-methyl-1-propene
c. 2 -iodo- 2 -methylpropane

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01:15

Problem 12

a. Which ether is most apt to form a peroxide?
b. Which ether is least apt to form a peroxide?

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01:56

Problem 13

Write the propagation steps for the addition of HBr to 1 -methylcyclohexene in the presence of a peroxide.

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01:15

Problem 14

What is the major product of the reaction of 2 -methyl- 2 -butene with each of the following reagents?
a. HBr
b. HCl
c. HBr + peroxide
d. HCl + peroxide

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01:33

Problem 15

a. What hydrocarbon with molecular formula $\mathrm{C}_{4} \mathrm{H}_{10}$ forms only two monochlorinated products? Both products are achiral.
b. What hydrocarbon with the same molecular formula as in part a forms three monochlorinated products? One is achiral and two are chiral.

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01:03

Problem 16

Draw the stereoisomers of the major monobromination products obtained from the following reaction.

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01:39

Problem 17

How many allylic substituted bromoalkenes are formed from the reaction of 2 -pentene with NBS? Disregard stereoisomers.

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01:18

Problem 18

Two products are formed when methylenecyclohexane reacts with NBS? Show how each is formed. Disregard stereoisomers.

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01:21

Problem 19

How many allylic substituted bromoalkenes are formed from the reactions in Problems 17 and 18 if stereoisomers are included?

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01:56

Problem 20

a. How many stereoisomers are formed from the reaction of cyclohexene with NBS?
b. How many stereoisomers are formed from the reaction of 3-methylcyclohexene with NBS?

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02:02

Problem 21

Draw the resonance contributors for the following radicals:

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03:12

Problem 22

a. Draw the major product(s) of the reaction of 1 -methylcyclohexene with the following reagents, disregarding stereoisomers:
1. NBS/ $\Delta /$ peroxide
2. $\mathrm{Br}_{2} / \mathrm{CH}_{2} \mathrm{Cl}_{2}$
3. HBr
4. HBr/peroxide
b. For each reaction, show which stereoisomers are obtained.

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04:18

Problem 23

Design a multistep synthesis to show how the following compounds can be prepared from the given starting material:

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02:03

Problem 24

How many atoms share the unpaired electron in semiquinone?

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02:01

Problem 25

Using resonance structures, explain why a catechin is an antioxidant.

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03:52

Problem 26

What are the product(s) of each of the following reactions? Disregard stereoisomers.

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01:23

Problem 27

a. What alkane, with molecular formula $\mathrm{C}_{5} \mathrm{H}_{12}$, forms only one monochlorinated product when it is heated with $\mathrm{Cl}_{2}$ ?
b. What alkane, with molecular formula $\mathrm{C}_{7} \mathrm{H}_{16}$, forms seven monochlorinated products (disregarding stereoisomers) when heated with $\mathrm{Cl}_{2}$ ?

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01:59

Problem 28

Explain why iodine $\left(\mathrm{I}_{2}\right)$ does not react with ethane, even though $\mathrm{I}_{2}$ is more easily cleaved homolytically than the other halogens.

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02:56

Problem 29

What is the major product obtained from treating an excess of each of the following compounds with $\mathrm{Cl}_{2}$ in the presence of ultraviolet light at room temperature? Disregard stereoisomers.

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02:21

Problem 30

What are the answers to Problem 29 when the same compounds are treated with $\mathrm{Br}_{2}$ at $125^{\circ} \mathrm{C} ?$

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04:07

Problem 31

What is the major product of the following reactions? Disregard stereoisomers:

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02:33

Problem 32

When 2-methylpropane is monochlorinated in the presence of light at room temperature, $36 \%$ of the product is 2 -chloro- 2 -methylpropane and $64 \%$ is 1-chloro-2-mcthylpropane. From these data, calculate how much easier it is to remove a hydrogen atom from a tertiary carbon than from a primary under these conditions.

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02:31

Problem 33

Draw all the monochlorination products, including stereoisomers, that are formed from radical chlorination of the following compound:

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01:47

Problem 34

Propose a mechanism to account for the products formed in the following reaction:

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01:11

Problem 35

The deuterium kinetic isotope effect for the halogenation of an alkane is defined in the following equation, where $X$. $=C 1 \cdot$ or $Br\cdot$
Predict whether chlorination or bromination would have a greater deuterium kinetic isotope effect.

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01:04

Problem 36

What are the major products of the following reaction?

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03:48

Problem 37

a. How many monochlorination products can be obtained from the radical chlorination of methylcyclohexane? Disregard stereoisomers.
b. Which product would be obtained in greatest yield? Explain.
c. How many monochlorination products would be obtained if all stereoisomers are included?

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01:47

Problem 38

a. What five-carbon alkene forms the same product whether it reacts with HBr in the presence of a peroxide or with HBr in the absence of a peroxide?
b. Draw the structures of four six-carbon alkenes that form the same product, whether they react with HBr in the presence of a peroxide or with HBr in the absence of a peroxide.

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02:59

Problem 39

What alkyl halide will be obtained in greatest yield? Ignore stereoisomers.

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03:55

Problem 40

Starting with cyclohexane, how could the following compounds be prepared?

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05:39

Problem 41

a. Propose a mechanism for the following reaction:
b. Given that $\Delta H^{\circ}$ for the reaction is $-42 \mathrm{kcal} / \mathrm{mol}$ and the bond dissociation enthalpies for the$\mathrm{C}-\mathrm{H}, \mathrm{C}-\mathrm{Cl},$ and $\mathrm{O}-\mathrm{H}$ bonds are $101,85,$ and 105 kcal/mol respectively, calculate the bond dissociation enthalpy of the $\mathrm{O}-\mathrm{Cl}$ bond.

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02:28

Problem 42

What stereoisomers are obtained from the following reaction?

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04:09

Problem 43

Using the given starting material and any necessary organic or inorganic reagents, indicate how the desired compounds could be synthesized:

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02:44

Problem 44

A chemist wanted to determine experimentally the relative ease of removing a hydrogen atom from a tertiary, a secondary, and a primary carbon by a chlorine radical. He allowed 2-methylbutane to undergo chlorination at $300^{\circ} \mathrm{C}$ and obtained as products $36 \%$ 1-chloro-2-methylbutane, $18 \%$ 2-choro:2-methylbutane.28\% 2:chloro-3-methylbutane, and 18\% 1-chloro:3-methylbutane. What values did he obtain for the relative ease of removing a hydrogen atom from tertiary, secondary, and primary hydrogen carbons by a chlorine radical under the conditions of his experiment?

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01:31

Problem 45

At $600^{\circ} \mathrm{C},$ the ratio of the relative rates of formation of a tertiary, a secondary, and a primary radical by a chlorine radical is $2.6: 2.1: 1 .$ Explain the change in the degree of regioselectivity compared to what was found in Problem 44.

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03:13

Problem 46

Draw the products of the following reactions, including all stereoisomers:

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03:38

Problem 47

a. Calculate the $\Delta H^{\circ}$ value for the following reaction:
$$\mathrm{CH}_{4}+\mathrm{Cl}_{2} \stackrel{h \nu}{\longrightarrow} \mathrm{CH}_{3} \mathrm{Cl}+\mathrm{HCl}$$
b. Calculate the sum of the $\Delta H^{\circ}$ values for the following two propagation steps:
$$\begin{array}{l}
\mathrm{CH}_{3}-\mathrm{H}+\cdot \mathrm{Cl} \longrightarrow \cdot \mathrm{CH}_{3}+\mathrm{H}-\mathrm{Cl} \\
\cdot \mathrm{CH}_{3}+\mathrm{Cl}-\mathrm{Cl} \longrightarrow \mathrm{CH}_{3}-\mathrm{Cl}+\cdot \mathrm{Cl}
\end{array}$$
c. Why do both calculations give you the same value of $\Delta H^{\circ} ?$

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02:20

Problem 48

A possible alternative mechanism to that shown in Problem 47 for the monochlorination of methane involves the following propagation steps:
$$\begin{array}{llll}
\mathrm{CH}_{3}-\mathrm{H}+\mathrm{Cl} & \longrightarrow & \mathrm{CH}_{3}-\mathrm{Cl}+\cdot \mathrm{H} \\
\cdot \mathrm{H}+\mathrm{Cl}-\mathrm{Cl} & \longrightarrow & \mathrm{H}-\mathrm{Cl}+\cdot \mathrm{Cl}
\end{array}$$
How do you know that the reaction does not take place by this mechanism?

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04:14

Problem 49

Propose a mechanism for the following reaction:

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02:24

Problem 50

Explain why the rate of bromination of methane decreases if $\mathrm{HBr}$ is added to the reaction mixture.

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02:19

Problem 51

Enediynes are natural products with potent antitumor propertics because they are able to cleave DNA (page 288). Their cytotoxic properties are duet the cnediyne undregoing a cyclization to form a highly reactive diradical intermediate. The intermediate abstracts hydrogen atoms from the backbone of DNA, which triggers its damage. Draw the structure of the diratical intermediate.

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