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CHM 332 > Radical Reactions > Flashcards

Radical Reactions Flashcards

1
Q
  1. Which of the following bonds has the lowest bond dissociation enthalpy?
    A. C-H
    B. C-F
    C. C-Br
    D. C-I
A

D. C-I

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2
Q
  1. Which of the following statements is not true?
    A. homolytic cleavage of a bond in a neutral molecule gives two radicals
    B. radicals have one or more unpaired electrons
    C. movement of single electrons is depicted using a “fishhook arrow”
    D. the C-F bond is the weakest bond between carbon atom and a halogen
A

D. the C-F bond is the weakest bond between carbon atom and a halogen

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3
Q
  1. Which halogen is most useful in the regioselective radical halogenation of alkenes??
    A. fluorine
    B. chlorine
    C. bromine
    D. iodine
A

C. bromine

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4
Q
  1. What is the major organic product obtained from the following reaction?
A

B) 2

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5
Q
  1. What is the major organic product obtained from the following reaction?
A

B) 2

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6
Q
  1. What is the major organic product obtained from the following reaction?
A

A) 1

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7
Q
  1. What are the major organic products obtained from the following reaction?
A

C. 1 and 3

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8
Q
  1. What is the correct order of stability of the following radicals (more stable > less stable)?
A

D. 3 > 2 > 1

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9
Q
  1. What is the correct order of stability of the following radicals (more stable > less stable)?
A

C. 2 > 3 > 1

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10
Q
  1. What is the characteristic of a radical chain initiation step?
    A. radicals are formed
    B. substitution products are formed
    C. a radical reacts with a molecule to give a new radical and a new molecule
    D. two radicals combine to give a molecule
A

A. radicals are formed

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11
Q
  1. What is the characteristic of a radical chain propagation step?
    A. radicals are formed
    B. byproducts are formed
    C. a radical reacts with a molecule to give a new radical and a new molecule
    D. two radicals combine to give a molecule
A

C. a radical reacts with a molecule to give a new radical and a new molecule

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12
Q
  1. What is the characteristic of a radical chain termination step?
    A. radicals are formed
    B. substitution products are formed
    C. a radical reacts with a molecule to give a new radical and a new molecule
    D. two radicals combine to give a molecule
A

D. two radicals combine to give a molecule

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13
Q
  1. What type of reactive intermediate is formed in the reaction of propene with N-bromosuccinimide to give 3-bromo-1-propene?
    A. allylic carbocation
    B. allylic carbanion
    C. allylic radical
    D. cyclic bromonium ion
A

C. allylic radical

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14
Q
  1. What type of reactive intermediate is formed upon irradiation of a solution of toluene (Ph-CH3) and bromine?
    A. benzylic carbocation
    B. benzylic carbanion
    C. benzylic radical
    D. cyclic bromonium ion
A

C. benzylic radical

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15
Q
  1. Which of the following alkanes does not undergo monobromination to form a single bromoalkane as the major product?
A

D) 4

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16
Q
  1. Which of the following alkenes undergoes allylic bromination to form a single monobrominated product?
A

A) 1

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17
Q
  1. What is the major product formed upon radical bromination of (S) 3-methylhexane?
    A. (S) 3-bromo-3-methylhexane
    B. (R) 3-bromo-3-methylhexane
    C. a mixture of (R) and (S) 3-bromo-3-methylhexane
    D. (3R) 1-bromo-3-methylhexane
A

C. a mixture of (R) and (S) 3-bromo-3-methylhexane

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18
Q
  1. What is the geometry of the central carbon atom of a tert-butyl radical?
    A. tetrahedral
    B. trigonal planar
    C. trigonal pyramidal
    D. square planar
A

B. trigonal planar

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19
Q
  1. Which of the following statements is not true about the allyl radical
    A. the carbon-carbon bond lengths are identical
    B. the unpaired electron density is shared between carbons 1 and 2.
    C. it undergoes reaction with bromine to give a single product
    D. it is formed by abstraction of a hydrogen atom from the methyl group of propene
A

B. the unpaired electron density is shared between carbons 1 and 2.

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20
Q
  1. How many electrons does the allyl radical have in p orbitals
    A. 1
    B. 2
    C. 3
    D. 4
A

C. 3

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21
Q
  1. How many p-bonding, non-bonding, and antibonding orbitals does the allyl radical possess?
    A. one bonding, one nonbonding, and one antibonding
    B. two bonding, no nonbonding, and no antibonding
    C. two bonding, one nonbonding, and no antibonding
    D. three bonding, no nonbonding, and no antibonding
A

A. one bonding, one nonbonding, and one antibonding

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22
Q
  1. What type of orbitals overlap to provide stability to the tert-butyl radical by hyperconjugation?
    A. 3 C 2p atomic orbital + 3 C sp2 atomic orbital
    B. 3 C 2p atomic orbital + methyl C-H s molecular orbital
    C. 3 C sp2 atomic orbital + methyl C-H s molecular orbital
    D. 3 C 2p atomic orbital + methyl C 2s atomic orbita
A

B. 3 C 2p atomic orbital + methyl C-H s molecular orbital

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23
Q
  1. What type of orbital contains the unpaired electron of the tert-butyl radical?
    A. s
    B. p
    C. sp3
    D. s
A

B. p

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24
Q
  1. Which of the following is an accurate statement of Hammond’s postulate?
    A. the transition state of an exothermic reaction will resemble the starting materials (reactants) more than the product
    B. the transition state of an exothermic reaction will resemble the products more than the starting materials (reactants)
    C. the transition state of an endothermic reaction will resemble the starting materials (reactants) more than the product
    D. the difference in energy between the starting materials (reactants) and transition state controls the rate of a reaction
A

A. the transition state of an exothermic reaction will resemble the starting materials (reactants) more than the product

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25
Q
  1. Which of the following statements is not true regarding the halogenation of alkanes upon treatment with halogen and light?
    A. bromination is more selective for 3 positions than chlorination
    B. the reaction proceeds via a radical intermediate
    C. the reaction proceeds via a chain reaction
    D. this is a useful process for the formation of fluorides, chlorides, bromides and iodides
A

D. this is a useful process for the formation of fluorides, chlorides, bromides and iodides

26
Q
  1. What type of reactive intermediate is formed in the reaction of propene with hydrogen bromide in the presence of peroxides to give 1-bromopropane?
    A. 1 radical
    B. 1 carbocation
    C. 1 radical
    D. 2 radical
A

D. 2 radical

27
Q
  1. What is the major product obtained from the reaction of 2-methyl-2-butene with hydrogen bromide in the presence of peroxides?
    A. 2,3-dibromo-2-methylbutane
    B. 2-bromo-3-methylbutane
    C. 2-bromo-2-methylbutane
    D. (E)-1-bromo-2-methyl-2-butene
A

B. 2-bromo-3-methylbutane

28
Q
  1. Which of the following statements is not true?
    A. Bromine radicals add to the least substituted end of a carbon-carbon double bond of an alkene.
    B. The major anti-Markovnikov product obtained upon addition of HBr to alkenes in the presence of a peroxide is formed in a radical termination step.
    C. Two radicals combine in radical termination steps.
    D. Alkoxy radicals remove a hydrogen atom from HBr to give an alcohol and a bromine atom.
A

B. The major anti-Markovnikov product obtained upon addition of HBr to alkenes in the presence of a peroxide is formed in a radical termination step.

29
Q
  1. Which of the following compounds is most susceptible to autooxidation?
    A. propene
    B. 1,3-butadiene
    C. 1,4-pentadiene
    D. 1,5-hexadiene
A

C. 1,4-pentadiene

30
Q
  1. What is the reactive intermediate in the autooxidation of cyclohexene?
    A. an allylic radical
    B. a 2 carbocation
    C. a carbocation
    D. a diene
A

A. an allylic radical

31
Q
  1. What is the major product of autooxidation of cyclohexene?
A

C) 3

32
Q
  1. What is the major organic product obtained from the following reaction?
A

C) 3

33
Q
  1. What is the major organic product obtained from the following reaction?
A

C. 3

34
Q
  1. What is the major organic product obtained from the following reaction?
A

A. 1

35
Q
  1. What are the major products formed upon treatment of (E) 3-methyl-2-hexene with HBr in the presence of peroxides?
A

D. a mixture of 1, 2, 3, and 4

36
Q
  1. What are the major products formed upon treatment of (E) 3-methyl-2-hexene with HBr in the absence of peroxides?
A

D. only 3

37
Q
  1. Which of the following accounts for the anti-Markovnikov regiochemistry of the reaction of an alkene with HBr in the presence of peroxides?
    A. the alkene reacts with HBr to give a carbocation
    B. the alkene reacts with a bromine atom to give a radical
    C. the alkene reacts with a hydrogen atom to give a radical
    D. the alkene reacts with peroxide to five an allylic radical
A

B. the alkene reacts with a bromine atom to give a radical

38
Q

3) The major type of reactions that alkanes undergo is ________.

A) electrophilic substitution reactions

B) electrophilic addition reactions

C) free radical substitution reactions

D) free radical addition reactions

E) nucleophilic substitution reactions

A

C) free radical substitution reactions

39
Q

4) Which of the following is the initiation step for the monobromination of cyclohexane?

A

D

40
Q

5) Which of the following is the rate-determining step for the monobromination of cyclohexane?

A

B) II

41
Q

10) What is the major product of the following reaction?

A

B) II

42
Q

14) The reaction Br2 + CH3Br → CH2Br2 + HBr was carried out. Which of the following mechanism steps is both productive and relatively likely to occur?

A) Br ∙ + ∙ CH2Br → CH2Br2

B) Br ∙ + ∙ CH3 → CH3Br

C) Br ∙ + Br2 → Br2 + Br ∙

D) Br ∙ + CH3Br → HBr + ∙ CH2Br

A

D) Br ∙ + CH3Br → HBr + ∙ CH2Br

43
Q

15) The reaction Br2 + CH3Br → CH2Br2 + HBr was carried out. Which of the following mechanism steps is productive, but relatively unlikely to occur?

A) Br ∙ + CH3Br → HBr + ∙ CH2Br

B) Br ∙ + ∙ CH2Br → CH2Br2

C) Br ∙ + Br2 → Br2 + Br ∙

D) Br ∙ + ∙ CH3 → CH3Br

A

B) Br ∙ + ∙ CH2Br → CH2Br2

44
Q

16) Which of the following reactions is a termination step in the free radical chlorination of methane?

A) Cl2 + Cl ∙ → Cl ∙ + Cl2

B) Cl2 → 2 Cl ∙

C) ∙ CH3 + Cl ∙ → CH3Cl

D) CH4 + Cl ∙ → HCl + ∙ CH3

A

C) ∙ CH3 + Cl ∙ → CH3Cl

45
Q

17) Which of the following is a chain propagation step in the free radical chlorination of methane?

A) CH4 + Cl ∙ → ∙ CH3 + HCl

B) Cl2 → 2 Cl ∙

C) Cl ∙ + ∙ CH3 → CH3Cl

D) ∙ CH3 + CH4 → CH4 + ∙CH3

A

A) CH4 + Cl ∙ → ∙ CH3 + HCl

46
Q

20) Which of the following does not occur in a propagation step in the free radical bromination of ethane to form bromoethane?

A) a C-H bond breaks

B) a Br-H bond forms

C) a C-Br bond forms

D) a Br-Br bond breaks

E) a C-C bond breaks

A

E) a C-C bond breaks

47
Q

32) Identify as initiation, propagation, or termination.

A

D) initiation = b; propagation = a, f; termination = c, d, e

48
Q

36) Which of the following is the most stable radical?

A

E

49
Q

37) What is the major product of the following reaction?

A

E) V

50
Q

38) Which of the following is not an intermediate or product in the reaction of

A

C) III

51
Q

39) Rank the free radicals (I-III) shown below in order of decreasing stability (i.e., from most stable to least stable).

A

B) II > III > I

52
Q

62) The major monobrominated product which results when methylcyclohexane is subjected to free radical bromination is ________.

A) a primary bromide

B) a secondary bromide

C) a tertiary bromide

D) a quaternary bromide

E) bromomethane

A

C) a tertiary bromide

53
Q

63) Which of the halogens below undergoes free radical halogenation with ethane most rapidly?

A) fluorine

B) chlorine

C) iodine

D) bromine

E) pyridine

A

A) fluorine

54
Q

64) In the free radical chlorination of ethane, the step in which the Cl radical abstracts a H atom from ethane is ________ and the transition state most closely resembles ________.

A) exothermic, the reactants

B) endothermic, the reactants

C) exothermic, the products

D) endothermic, the products

E) endothermic, a carbocation

A

A) exothermic, the reactants

55
Q

70) What is the major product of the following reaction?

A

D) IV

56
Q

71) What is the major product of the following reaction?

A

C) III

57
Q

72) Which of the following is a step in the mechanism of the reaction shown?

A

A

58
Q

73) A radical mechanism is postulated to occur when cyclohexene reacts under which of the following conditions?

A) Br2, CCl4

B) H+, H2O

C) BH3∙THF

D) HBr, peroxide

E) Hg(OAc)2, H2O

A

D) HBr, peroxide

59
Q

74) Which of the following is the best synthesis of 1, 1-dibromopropane?

A

D

60
Q

80) Give the best product for the following reaction.

A

A

61
Q

81) Give the best product for the following reaction.

A

B

62
Q

93) What reagent can best be used to convert cyclopentene to 3-bromocyclopentene in a single step?

A) Br2, hυ

B) NBS, Δ

C) HBr

D) HBr with peroxide

E) none of the above

A

B) NBS, Δ

CHM 332 (12 decks)

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