Chapter 10: Free Radicals: Answers
Prof. Jayaraman Sivaguru
Chapter 10: Free Radicals
1. Chlorination of pentane gives a mixture of isomers having the molecular formula
C5H11Cl. The percentage of 1-chloropentane is 22%. Assuming the secondary
hydrogens in pentane are equally reactive to monochlorination, what is the percentage
of 3-chloropentane in the mixture?
A) 48% B) 26% C) 22% D) 14%
Ans: B
2. Which one of the following gives a single monochlorination product?
A) 2,2-dimethylpropane
C) 2,3-dimethylbutane
B) 2,2-dimethylbutane
D) 2-methylpropane
Ans: A
3. Which of the following hydrocarbons has the slowest reaction rate with Br2 and light?
A) CH4 B) CH3CH2CH3 C) CH3CH2CH2CH3 D) (CH3)3CH
Ans: A
4. Which of the following is not a good method to make bromocyclopentane?
A) cyclopentanol plus HBr
C) cyclopentanol plus PBr3
B) cyclopentanol plus NaBr
D) cyclopentane plus Br2 with light
Ans: B
5. How many monochlorination products do you expect in the following reaction?
A) two B) three C) four
Ans: C
D) five
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Chem 341: Organic Chemistry, Prof. Jayaraman Sivaguru, Fall 2016.
Chapter 10: Free Radicals: Answers
Prof. Jayaraman Sivaguru
6. Which of the following is the most stable radical?
A) A B) B
Ans: A
C) C
D) D
7. Which of the following are the chain propagating steps in the free radical chlorination of
methane?
A) I and III
Ans: D
B) II and VI
C) III and IV
D) III and V
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Chem 341: Organic Chemistry, Prof. Jayaraman Sivaguru, Fall 2016.
Chapter 10: Free Radicals: Answers
Prof. Jayaraman Sivaguru
8. Calculate ΔH° of reaction for the free radical bromination of cyclopentane to give
bromocyclopentane.
A) –121 kJ/mol B) –63 kJ/mol C) +121 kJ/mol D) +63 kJ/mol
Ans: B
9. Which constitutional isomer of C6H14 gives only two monochlorination products?
A) 2-methylpentane
C) 2,2-dimethylbutane
B) 3-methylpentane
D) 2,3-dimethylbutane
Ans: D
10. Consider the following reaction (X = Cl or Br).
Which statement(s) is(are) correct?
I. Statistically the 1-halopropane should be the major isomer.
II. The 2-halopropane to 1-halopropane ratio is largest when X=Br.
III. The 2-halopropane to 1-halopropane ratio is the largest when X=Cl.
A) only II B) only III C) I and II D) I and III
Ans: C
11. Studies indicate that the methyl radical is trigonal planar. Based on this, which of the
following best describes the methyl radical?
A) The carbon is sp2 hybridized and the unpaired electron occupies an sp2 orbital.
B) The carbon is sp2 hybridized and the unpaired electron occupies a 2p orbital.
C) The carbon is sp3 hybridized and the unpaired electron occupies an sp3 orbital.
D) The carbon is sp3 hybridized and the unpaired electron occupies a 2p orbital.
Ans: B
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Chem 341: Organic Chemistry, Prof. Jayaraman Sivaguru, Fall 2016.
Chapter 10: Free Radicals: Answers
Prof. Jayaraman Sivaguru
12. Dibromination of isopropylcyclopentane gives a product which can be isolated in good
yields. Which of the following would you predict to be this product?
A) A B) B
Ans: B
C) C
D) D
13. Which of the following is the key intermediate in the chlorination reaction below?
A) A B) B
Ans: B
C) C D) D
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Chem 341: Organic Chemistry, Prof. Jayaraman Sivaguru, Fall 2016.
Chapter 10: Free Radicals: Answers
Prof. Jayaraman Sivaguru
14. Upon free-radical chlorination, the alkane shown would yield
C
C
C
C
C
A) a single monochloride
B) two isomeric dichlorides
Ans: D
C)
D)
three isomeric monochlorides
four isomeric monochlorides
15. What is the major product in the mono-chlorination of pentane?
Cl
Cl
C C C C C
A
A) A B) B
Ans: B
Cl
C C C C C
C C C C C
B
C
C) C
D) D
D. none of these is formed.
16. The reaction shown below is what type?
Cl•
+
CH4
A) addition
Ans: C
B) termination
HCl + H3C•
C) propagation
D) initiation
17. Which halogen forms the weakest bond to carbon?
A) F B) Cl C) Br D) I
Ans: A
18. If you wanted to get the best yield of compound B from compound A, you would:
?
X
compound A
compound B
A) use chlorine + light rather than bromine + light
B) use bromine + light rather than chlorine + light
C) neither would give >50% yield
D) either would give >50% yield
Ans: A
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Chem 341: Organic Chemistry, Prof. Jayaraman Sivaguru, Fall 2016.
Chapter 10: Free Radicals: Answers
Prof. Jayaraman Sivaguru
19. Where would this reaction occur fastest in this molecule?
A
B
Br2
?
light
D
C
A) A B) B
Ans: A
C) C
D) D
20. Which species below is the intermediate in the free radical addition of HBr to 1-butene?
A) A B) B
Ans: C
C) C
D) D
21. Determine the SODAR (sum of double bonds and rings) for a compound with the
formula of C6H9BrO.
A) one B) two C) three D) four
Ans: B
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Chem 341: Organic Chemistry, Prof. Jayaraman Sivaguru, Fall 2016.
Chapter 10: Free Radicals: Answers
Prof. Jayaraman Sivaguru
22. Which of the following does not give 1-bromo-1-methylcyclopentane as the major
product?
A) A B) B
Ans: A
C) C
D) D
23. Identify the following polymer.
A) polyethylene B) polypropylene C) polyisobutylene D) polybutylene
Ans: B
24. The polymerization of styrene gives a polymer that has which structure?
styrene
Ph
A.
Ph
Ph
n
Ph
B.
Ph
Ph
Ph
Ph
n
Ph
Ph
C.
D. none of these
Ph
A) A B) B
Ans: A
Ph
C) C
n
D) D
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Chem 341: Organic Chemistry, Prof. Jayaraman Sivaguru, Fall 2016.