Deck 15: Radical Reactions

Question 1

Which of the following statements about radical reactions is not true?

A) Light or heat provides the energy needed for homolytic bond cleavage to form radicals.
B) Breaking the weak O-O bond of peroxides initiates radical reactions.
C) The diradical O₂ removes radicals from a reaction mixture.
D) Radicals rearrange.

Answer 1

Radicals rearrange.

Question 2

What is the product in the following sequence of reactions?

A) I
B) II
C) III
D) IV

Answer 2

I

Question 3

How many monochlorination products can be formed (constitutional isomers only) from the reaction of CH₃CH₂CH₂CH₂CH₂CH₃ with Cl₂ and hv?

A) 3
B) 4
C) 5
D) 6

Answer 3

3

Question 4

Which of the following is a radical scavenger?

A) O₃
B) O₂
C) Vitamin C
D) CO₂

Question 5

Which of the following statements about the stereochemistry of halogenation reactions is true?

A) An achiral starting material always gives an achiral product only.
B) An achiral starting material always gives a racemic product only.
C) The configuration at a stereogenic center of a product must change even if a reaction does not occur at a stereogenic center.
D) An achiral starting material always gives either an achiral or a racemic product.

Question 6

Which of the following statements about chlorination is true?

A) The rate-determining step in chlorination is endothermic.
B) The transition state resembles the product.
C) The more stable radical is formed faster.
D) A mixture of products results.

Question 7

Which of the following statements about the propagation steps in the chlorination of ethane is true?

A) Radical chlorination consists of two propagation steps.
B) The energy diagram for the propagation steps has three energy barriers.
C) The first of the propagation steps is rate-determining because its transition state is at lower energy.
D) The second of the propagation steps is rate-determining because its transition state is at higher energy.

Question 8

Which step is the rate-determining step in the mechanism of radical halogenation?

A) Initiation
B) Propagation
C) Termination
D) Initiation and Propagation

Question 9

Which of the following statements about carbon radicals is not true?

A) Carbon radicals are classified as primary, secondary, tertiary, or quaternary.
B) A carbon radical is sp² hybridized.
C) The geometry of a carbon radical is trigonal planar.
D) The unhybridized p orbital in a carbon radical contains the unpaired electron.

Question 10

Which of the following statements about radicals is true?

A) Cleavage of a stronger bond forms the more stable radical.
B) The stability of a radical increases as the number of alkyl groups bonded to the radical carbon decreases.
C) The higher the bond dissociation energy for a C-H bond, the more stable the resulting carbon radical.
D) Less stable radicals generally do not rearrange to more stable radicals.

Question 11

How many monochlorination products can be formed (constitutional isomers only) from the reaction of (CH₃)₂CHCH₂CH₃ with Cl₂ and hv?

A) 2
B) 3
C) 4
D) 5

Question 12

Which of the following statements about radicals and radical reactions is not true?

A) Most radicals are unstable.
B) A radical contains an atom that has an octet of electrons.
C) Half-headed arrows are used to show the movement of lone electrons.
D) A radical is formed by homolysis of a covalent bond.

Question 13

Which of the following statements about chlorination and bromination is true?

A) Bromination is unselective, yielding a mixture of products.
B) Chlorination is often selective, yielding one major product.
C) Chlorination is faster than bromination.
D) Bromination is faster than chlorination.

Question 14

How many monochlorination products can be formed from the reaction of (CH₃)₃CH with Cl₂ and hv?

A) 1
B) 2
C) 3
D) 4

Question 15

What is the product in the following sequence of reactions?

A) I
B) II
C) III
D) IV

Question 16

Which of the following compounds contain primary (1°) radical carbons?

A) Only I
B) Only II
C) Only III
D) Only II and IV

Question 17

Which of the following compounds contain tertiary (3°) radical carbons?

A) Only I
B) Only II
C) Only III
D) Only II and IV

Question 18

Which of the following compounds contain secondary (2°) radical carbons?

A) Only I
B) Only II
C) Only III
D) Only II and IV

Question 19

Which of the following statements about bromination is true?

A) The rate-determining step in bromination is exothermic.
B) Both radicals are formed.
C) A mixture of products results.
D) A single radical halogenation product predominates.

Question 20

How many monochlorination products (constitutional isomers and stereoisomers) are formed from the reaction of butane with Cl₂ and hv?

A) 2
B) 3
C) 4
D) 5

Question 21

Identify the monomer used to make the following polymer.

A) I
B) II
C) III
D) IV

Question 22

Determine the monochlorination product(s)

A) Only I
B) Only II
C) Only III
D) Only I and II

Question 23

What is the product of the following reaction?

A) I
B) II
C) III
D) IV

Question 24

Which of the labeled hydrogens is most easily abstracted in a free radical bromination reaction?

A) H_a
B) H_b
C) H_c
D) H_d

Question 25

Identify the monomer used to make the following polymer.

A) I
B) II
C) III
D) IV

Question 26

Rank the following radicals in order of decreasing stability, putting the most stable first. $\mathrm { CH } _ { 3 } \dot { \mathrm { C } } \mathrm { H } _ { 2 }\quad$ $\mathrm { H } _ { 2 } \mathrm { C } = \mathrm { C } \dot { \mathrm { C } } \mathrm { H } _ { 2 }\quad$ $\mathrm { CH } _ { 3 } \dot { \mathrm { C } } \mathrm { HCH } _ { 3 }\quad$ $\left( \mathrm { CH } _ { 3 } \right) _ { 3 } \dot { \mathrm { C } }$
I $\quad\quad\quad\quad\quad\quad\quad$ II $\quad\quad\quad\quad\quad\quad\quad$ III $\quad\quad\quad\quad\quad$ IV

A) II > IV > III > I
B) III > II > IV > I
C) IV > III > II > I
D) IV > III > I > II

Question 27

Rank the following radicals in order of increasing stability, putting the least stable first.

A) III < I < II
B) I < II < III
C) III < II < I
D) I < III < II

Question 28

How many monochlorination products (constitutional isomers and stereoisomers) are formed from the reaction of pentane with Cl₂ and hv?

A) 2
B) 3
C) 4
D) 5

Question 29

A possible reaction of ethane with chlorine is shown below. $$\mathrm { CH } _ { 3 } \mathrm { CH } _ { 3 } + \mathrm { Cl } _ { 2 } \longrightarrow \mathrm { CH } _ { 3 } \mathrm { CH } _ { 2 } \mathrm { Cl } + \mathrm { HCl }$$ This reaction could conceivably occur by the following chain mechanisms [1], [2], and [3]. Determine $\Delta$ H for step [2]. [1] $\quad \mathrm { Cl } _ { 2 } \longrightarrow 2 \mathrm { Cl } \cdot$
[2] $\mathrm { Cl } ^ { \cdot } + \mathrm { CH } _ { 3 } \mathrm { CH } _ { 3 } \stackrel { \text { slow } } { \longrightarrow } \mathrm { HCl } + \mathrm { CH } _ { 3 } \mathrm { CH } _ { 2 } ^ \cdot$
$[ 3 ] \mathrm { CH } _ { 3 } \mathrm { CH } _ { 2 } ^ \cdot + \mathrm { Cl } _ { 2 } \stackrel { \text { fast } } { \longrightarrow } \mathrm { CH } _ { 3 } \mathrm { CH } _ { 2 } \mathrm { Cl } + \mathrm { Cl } ^\cdot$ Bond dissociation energies (kcal/mol): $$\begin{array} { | l l | } \hline \text { Bond A-B } & \Delta \mathrm { H } \\\hline \mathrm { Cl } - \mathrm { Cl } & 58 \\\mathrm { CH } _ { 3 } - \mathrm { H } & 104 \\\mathrm { CH } _ { 3 } \mathrm { CH } _ { 2 } - \mathrm { H } & 98 \\\mathrm { CH } _ { 3 } \mathrm { CH } _ { 3 } & 88 \\\mathrm { CH } _ { 3 } \mathrm { CH } _ { 2 } - \mathrm { Cl } & 81 \\\mathrm { H } - \mathrm { Cl } & 103 \\\hline\end{array}$$

A) -5 kcal/mol
B) +58 kcal/mol
C) -28 kcal/mol
D) None of the choices are correct.

Question 30

Which of the following statements is (are) true about free radical halogenation of alkanes?

A) The first of the chain-propagating steps is rate-determining.
B) The reaction proceeds by way of a flat sp² hybridized free radical.
C) The chain-initiating step involves cleavage of a carbon-hydrogen bond to afford a carbon radical and a hydrogen atom.
D) Statements (The first of the chain-propagating steps is rate-determining) and (The reaction proceeds by way of a flat sp² hybridized free radical) are both true.

Question 31

Identify the monomer used to make the following polymer.

A) I
B) II
C) III
D) IV

Question 32

Determine the product(s) of the following reaction.

A) Only I
B) Only II
C) Only III
D) Only I and II

Question 33

Which of the indicated hydrogens is most readily abstracted in a free radical halogenation reaction?

A) I
B) II
C) III
D) IV

Question 34

A possible reaction of ethane with chlorine is shown below. $$\mathrm { CH } _ { 3 } \mathrm { CH } _ { 3 } + \mathrm { Cl } _ { 2 } \longrightarrow \mathrm { CH } _ { 3 } \mathrm { CH } _ { 2 } \mathrm { Cl } + \mathrm { HCl }$$ This reaction could conceivably occur by the following chain mechanisms [1], [2], and [3]. The chain propagating step(s) is (are) _______. $[ 1 ] \quad \mathrm { Cl } _ { 2 } \longrightarrow 2 \mathrm { Cl } \cdot$
[2] $\mathrm { Cl } \cdot + \mathrm { CH } _ { 3 } \mathrm { CH } _ { 3 } \stackrel { \text { slow } } { \longrightarrow } \mathrm { HCl } + \mathrm { CH } _ { 3 } \mathrm { CH } _ { 2 }^ \cdot$
[3] $\mathrm { CH } _ { 3 } \mathrm { CH } _ { 2 } ^\cdot + \mathrm { Cl } _ { 2 } \stackrel { \text { fast } } { \longrightarrow } \mathrm { CH } _ { 3 } \mathrm { CH } _ { 2 } \mathrm { Cl } + \mathrm { Cl }\cdot$ .

A) Only [1] and [2]
B) Only [2] and [3]
C) Only [1] and [3]
D) Only [3]

Question 35

What is the product of the following reaction?

A) I
B) II
C) III
D) IV

Question 36

How many allylic halides can be formed when 3-methycyclohexene undergoes allylic halogenation with one equivalent of NBS and light?

A) 1
B) 2
C) 3
D) 4

Question 37

What is the product of the following reaction?

A) I
B) II
C) III
D) IV

Question 38

A possible reaction of ethane with chlorine is shown below. $$\mathrm { CH } _ { 3 } \mathrm { CH } _ { 3 } + \mathrm { Cl } _ { 2 } \longrightarrow \mathrm { CH } _ { 3 } \mathrm { CH } _ { 2 } \mathrm { Cl } + \mathrm { HCl }$$ This reaction could conceivably occur by the following chain mechanisms [1], [2], and [3]. Determine $\Delta$ H for step [1]. [1] $\mathrm { Cl } _ { 2 } \longrightarrow 2 \mathrm { Cl } \cdot$
[2] $\mathrm { Cl } \cdot + \mathrm { CH } _ { 3 } \mathrm { CH } _ { 3 } \stackrel { \text { slow } } { \longrightarrow } \mathrm { HCl } + \mathrm { CH } _ { 3 } \mathrm { CH } _ { 2 } ^ \cdot$
[3] $\mathrm { CH } _ { 3 } \mathrm { CH } _ { 2 } ^ \cdot+ \mathrm { Cl } _ { 2 } \stackrel { \text { fast } } { \longrightarrow } \mathrm { CH } _ { 3 } \mathrm { CH } _ { 2 } \mathrm { Cl } + \mathrm { Cl }\cdot$ . Bond dissociation energies (kcal/mol): $$\begin{array} { | l | l | } \hline \text { Bond A-B } & \Delta \mathrm { H } \\\hline \mathrm { Cl } - \mathrm { Cl } & 58 \\\mathrm { CH } _ { 3 } - \mathrm { H } & 104 \\\mathrm { CH } _ { 3 } \mathrm { CH } _ { 2 } - \mathrm { H } & 98 \\\mathrm { CH } _ { 3 } - \mathrm { CH } _ { 3 } & 88 \\\mathrm { CH } _ { 3 } - \mathrm { Cl } & 84 \\\mathrm { H } - \mathrm { Cl } & 103 \\\hline\end{array}$$

A) -5 kcal/mol
B) +58 kcal/mol
C) -28 kcal/mol
D) None of the choices are correct.

Question 39

Determine the product of the following reaction.

A) I
B) II
C) III
D) IV

Question 40

A possible reaction of ethane with chlorine is shown below. $$\mathrm { CH } _ { 3 } \mathrm { CH } _ { 3 } + \mathrm { Cl } _ { 2 } \longrightarrow \mathrm { CH } _ { 3 } \mathrm { CH } _ { 2 } \mathrm { Cl } + \mathrm { HCl }$$ This reaction could conceivably occur by the following chain mechanisms [1], [2], and [3]. The chain initiating step(s) is (are) _____. [1] $\mathrm { Cl } _ { 2 } \longrightarrow 2 \mathrm { Cl }^*$ .
[2] $\mathrm { Cl } ^* + \mathrm { CH } _ { 3 } \mathrm { CH } _ { 3 } \stackrel { \text { slow } } { \longrightarrow } \mathrm { HCl } + \mathrm { CH } _ { 3 } \mathrm { CH } _ { 2 }^*$ .
[3] $\mathrm { CH } _ { 3 } \mathrm { CH } _ { 2 } ^ { * } + \mathrm { Cl } _ { 2 } \stackrel { \text { fast } } { \longrightarrow } \mathrm { CH } _ { 3 } \mathrm { CH } _ { 2 } \mathrm { Cl } + \mathrm { Cl }^*$ .

A) Only [1]
B) Only [2]
C) Only [3]
D) Only [1] and [2]

Question 41

Select the route that would most likely produce the desired results from the given starting material. I. (1) H₂SO₄ and heat; (2) HBr II. (1) KOH in ethanol; (2) HBr
III) (1) H₂SO₄ and heat; (2) HBr + peroxides
IV) (1) potassium tert-butoxide in tert-butanol; (2) HBr + peroxides

A) I
B) II
C) III
D) IV

Question 42

Which of the following alkenes undergoes allylic bromination to form a single monobrominated product?

A) I
B) II
C) III
D) IV

Question 43

What type of reactive intermediate is formed in the reaction of propene with N-bromosuccinimide (NBS) to give 3-bromo-1-propene?

A) Cyclic bromonium ion
B) Allylic carbocation
C) Allylic carbanion
D) Allylic radical