Deck 12: Radical Reactions

Question 1

What is a radical inhibitor?

A)a chemical species that prevents an initiation step in a radical chain reaction
B)a chemical species that terminates the chain in a radical chain reaction
C)a chemical species that prevents chain termination in a radical chain reaction
D)a chemical species that accelerates one or more propagation steps in a radical chain reaction
E)a chemical species that produces radicals

Answer 1

a chemical species that terminates the chain in a radical chain reaction

Question 2

Which of the following transformations is a disproportionation?

A)
B)
C)
D)
E)

Answer 2

Question 3

Which of the following is least likely to be a radical initiator?

A)
B)
C)
D)
E)

Answer 3

Question 4

Which of the following statements about the anti-Markovnikov addition of HX to alkenes is false?

A)The reaction is typically run in the presence of peroxides and/or other radical initiators.
B)The regiochemistry is the result of the formation of the most substituted carbocation in the rate-limiting step.
C)The halogen atom attaches to the less substituted end of the alkene.
D)The reaction is only successful when HBr is used.
E)An alcohol is formed as a byproduct.

Question 5

Cyclopropylmethyl radical, shown here, decomposes rapidly through a β cleavage process. Which of the following structures is the product of this process?

A)
B)
C)
D)
E)

Question 6

Which is the following would not be a valid resonance form for this radical?

A)
B)
C)
D)
E)

Question 7

Which of the following do you expect is least likely to act as a radical inhibitor?

A)
B)
C)
D)
E) All these molecules are equally likely to act as radical inhibitors.

Question 8

The disproportionation product(s) of the alkyl radical shown here will be

A) two alkanes.
B) an alkane and an alkene.
C) one alkane.
D) one alkene.
E) two alkenes.

Question 9

Which of these would not be expected to be a product from radical reaction of the cyclopentyl radical?

A)

B)

C)

D)

E)

Question 10

Which of the indicated C-C bonds requires the least amount of energy to break homolytically?

A) A
B) B
C) C
D) D
E) E

Question 11

What orbitals are involved in hyperconjugative stabilization of the radical shown here?

A) filled and empty
B) filled and empty
C) filled and half-filled
D) filled and half-filled
E) filled and empty

Question 12

Which of the following monomers will react to provide the polymer shown here?

A)
B)
C)
D)
E)

Question 13

What is the most likely stereochemical outcome of the following reaction?

A) an unequal mixture of enantiomers
B) an equal mixture of enantiomers
C) an unequal mixture of diastereomers
D) an equal mixture of diastereomers
E) Choices b and d are equally likely.

Question 14

Which of the following radicals is most stable?

A)
B)
C)
D)
E)

Question 15

Which of the following methods could not be used to facilitate radical formation?

A)inducing strain in a molecule to weaken sigma bonds
B)treating the molecule with a highly hindered base
C)starting with a molecule that will yield highly stabilized radicals on cleavage
D)starting with a molecule with an exceptionally weak sigma bond
E)treating the starting material with a radical initiator

Question 16

What is the name of the process shown here?

A) disproportionation
B) hydrogen abstraction
C) β cleavage
D) dimerization
E) pyrolysis

Question 17

Which of the following is a termination step in a radical chain reaction?

A)
B)
C)
D)
E)

Question 18

Which of these would be the expected product of the following reaction?

A)
B)
C)
D)
E)

Question 19

Which bond is easiest to break homolytically? (For clarity, not all bonds in the molecule are shown.)

A) A
B) B
C) C
D) D
E) E

Question 20

What are the products of β cleavage of the radical species shown?

A)
B)
C)
D)
E)

Question 21

Which of the following concepts should be used to correctly describe the reason for enhanced regioselectivity of photobromination versus photochlorination?

A) relative bond strengths of Cl₂ and Br₂.
B) energy released on termination steps
C) overall enthalpy of reaction
D) Hammond postulate
E) steric hindrance

Question 22

Which of the following statements about allylic bromination using NBS is false?

A)Molecular bromine concentration must be low.
B)Allylic rearrangements may occur.
C)HBr is required in trace amounts.
D)Symmetrical alkenes are the most suitable substrates for the reaction to avoid mixtures of products.
E)Bromine radical is produced by homolytic cleavage of the N-Br bond in N-bromosuccinimide.

Question 23

Predict the product of the following reaction.

A)
B)
C)
D)
E) both b and d

Question 24

Which of the following is a propagation sep?

A)
B)
C)
D)
E)

Question 25

Predict the product of the following reaction.

Question 26

Draw an arrow-pushing mechanism for the transformation shown here.

Question 27

What would be expected to be the major organic product from the following reaction?

A)
B)
C)
D)
E)

Question 28

When a sample of diethyl ether is allowed to stand, over time it reacts with molecular
oxygen to form peroxides.
Propose an arrow-pushing mechanism to illustrate the formation of the peroxide from the ether starting material. Use as the initiator. Show all curved arrows and single electrons.

Question 29

Which of the following monobrominated products forms fastest under the conditions shown?

A)
B)
C)
D)
E) All form at equal rates.

Question 30

Which of the following compounds is the product of this reaction?

A)
B)
C)
D)
E) Both a and b would be produced.

Question 31

Predict the most likely products of β cleavage of the radical shown here and draw an arrow-pushing mechanism to illustrate their formation.

Question 32

Which of the following statements about rearrangements is false?

A)Hydrogen atom shifts in radicals are not observed.
B)1,2-vinyl group shifts in radicals have been observed.
C)Methyl group shifts in radicals are not observed.
D)Radical rearrangements are disfavored because the transition state for the rearrangement is destabilized.
E)Carbocation rearrangements are favored because the transition state for the rearrangement is stabilized.

Question 33

What is the stereochemical outcome of the following reaction?

A)Enantiomers are produced in equal amounts.
B)Diastereomers are produced in equal amounts.
C)A single product forms.
D)Enantiomers are produced in unequal amounts.
E)Diastereomers are produced in unequal amounts.

Question 34

Devise a multistep synthesis of the target molecule from the given starting material.Show the
reagents needed for each step and the product of each step.

Question 35

Devise a multistep synthesis of the target molecule from the given starting material. Show the reagents needed for each step and the product of each step.

Question 36

Devise a multistep synthesis of the target molecule from the given starting material.Show the
reagents needed for each step and the product of each step.

Question 37

For the free radical chloriation of 2-methylbutane, estimate the expected percentage of each product shown.

A) A -25 % ; B -17 % ; C -8 % ; D -50 %
B) A-13 % ; B-44 % ; C-17 % ; D-26 %
C) A - 28 % ; B - 14 % ; C - 2 % ; D - 56 %
D) A - 14 % ; B -36 % ; C -23 % ; D -27 %
E) A -28 % ; B -5 % ; C -12 % ; D -55 %

Question 38

Unsaturated fats in food react with oxygen to form alkylperoxy radicals.These radicals can then
react further with compounds in the food to degrade its taste.To prevent this process,
preservatives like BHT (butylated hydroxytoluene) that act as radical inhibitors are added to some
foods.

Question 39

Draw the products of the following reaction.

Question 40

Predict the major product from addition of two equivalents of HBr in the following reaction.

A)
B)
C)
D)
E)

Question 41

Draw all the constitutional isomers of the monochloroalkane generated from the free radical
chlorination of methylcyclohexane.Which of the constitutional isomers would also have
stereoisomers?

Question 42

S-6-Bromo-1,6-dimethylcyclohexene reacts with hydrogen bromide in the absence of
radical-inducing conditions to produce two major isomers, one of which is optically active; the
other is meso.Draw the stereoisomers that can be produced if the same reaction is performed in
the presence of the radical initiator AIBN.

Question 43

Devise a multistep synthesis of the target molecule from the given starting material.Show the
reagents needed for each step and the product of each step.

Question 44

A chemist would like to prepare a tertiary alcohol via the following reaction sequence.

What halogen X should be used to ensure the maximum selectivity for the intermediate haloalkane?

Question 45

Draw the two organic products formed from the reaction between 3-methylcyclohexene and
N-bromosuccinimide under the conditions shown.

Question 46

Draw the stepwise mechanism for the free radical chlorination of cyclobutane to produce
chlorocyclobutane.Identify initiation and propagation steps; give one example of a termination
step.Use single-side curved arrows to show the movement of single electrons.

Question 47

Anti-Markovnikov addition of HX to an alkene only works with HBr in the presence of peroxides
as a radical initiator.Use the bond dissociation data provided to explain why the reaction fails
with HCl and HI.

Question 48

What is the principal monobrominated product that would result from the conditions shown?

Question 49

Provide an arrow-pushing mechanism for the formation of polystyrene from styrene in the presence of AIBN.

Question 50

Predict the product of the following reaction.

Question 51

Draw an arrow-pushing mechanism to show the transformation of dibromomethane to bromoform in
the presence of molecular bromine and bromine radical.

Question 52

Using the bond dissociation energies provided below, draw an energy diagram for the two
propagation steps in the following reaction.
Show the correct relative energies of intermediates, starting materials and products. Estimate the
Bond dissociation energies (kcal/mol)

Question 53

Provide the structures of all monochlorinated products that would result from the conditions
shown.Assume that all chiral products are formed as racemic mixtures.

Question 54

Predict the product of the following reaction.

Question 55

Draw the products of the following reaction; indicate major and minor products.

Question 56

In a radical chain reaction, termination steps are exothermic, yet propagation steps can be
endothermic.Despite this energetic difference, propagation steps can compete successfully to
continue the chain reaction, resulting in the eventual product.Explain.

Question 57

Devise a multistep synthesis of the target molecule from the given starting material.Show the
reagents needed for each step and the product of each step.Explain why the target cannot be made
from the starting material in one step.

Question 58

Draw the mechanism for the following free radical chain reaction.Clearly indicate initiation and
propagation steps; show one possible termination step.

Question 59

Devise a multistep synthesis of the target molecule from the given starting material.Show the
reagents needed for each step and the product of each step.Explain why the first step requires free
radical conditions.

Question 60

Draw the major product of this synthetic sequence.

Question 61

Predict the major organic product and provide a mechanism to illustrate its formation under the conditions shown.Show all curved arrows, lone pairs, and single electrons, and any nonzero formal charges.

Question 62

In an allylic bromination, why is it essential to keep the concentration of molecular bromine relatively low?

Question 63

Devise a multistep synthesis of the target molecule from the given starting material.Show the
reagents needed for each step and the product of each step.

Question 64

Devise a multistep synthesis of the target molecule from the given starting material.Show the
reagents needed for each step and the product of each step.

Question 65

Predict the product of the following sequence of reactions.