Q: Which of the following correctly ranks the stability of alkyl radicals from least to most stable?

$$\text{Methyl} \u003c \text{Primary} \u003c \text{Secondary} \u003c \text{Tertiary}$$

Question 1

Which of the following statements best describes a free radical?

Accepted Answer

A species with an unpaired electron and is neutral.

Question 2

Which of the following correctly ranks the stability of alkyl radicals from least to most stable?

Accepted Answer

$$	ext{Methyl} \u003c 	ext{Primary} \u003c 	ext{Secondary} \u003c 	ext{Tertiary}$$

Question 3

What is the main difference between homolytic and heterolytic bond cleavage?

Accepted Answer

Homolytic cleavage produces two radicals, while heterolytic cleavage produces a cation and an anion.

Question 4

Which of the following best explains why bromination of alkanes is more regioselective than chlorination?

Accepted Answer

Bromine is less reactive and more selective, favoring the formation of the most stable radical intermediate.

Question 5

During the free-radical halogenation of methane, which step is responsible for the propagation of the chain reaction?

Accepted Answer

Hydrogen atom abstraction from methane by a chlorine atom, forming methyl radical and HCl.

Question 6

In the free-radical addition of HBr to 1-butene in the presence of peroxides, what is the major product and why?

Accepted Answer

1-Bromobutane, because anti-Markovnikov addition occurs due to the free radical mechanism.

Question 7

Which of the following best describes the hybridization and geometry of the methyl radical ($$\cdot\mathrm{CH}_3$$)?

Accepted Answer

sp$$^2$$ hybridized, planar geometry

Question 8

Which of the following statements about bond dissociation enthalpy (BDE) is correct?

Accepted Answer

A lower BDE means the bond is weaker and easier to break homolytically.

Question 9

A chemist wants to synthesize 1-bromo-2,3,3-trimethylbutane from 2,2,3-trimethylbutane. Which sequence of reactions would achieve this transformation?

Accepted Answer

Brominate 2,2,3-trimethylbutane at the 1-position using Br$$_2$$ and light.

Question 10

Which of the following is a correct statement about the sodium-ammonia reduction of alkynes?

Accepted Answer

It produces trans-alkenes as the major product.

Question 11

In the free-radical polymerization of ethylene, what is the role of the peroxide?

Accepted Answer

It initiates the reaction by generating free radicals.

Question 12

Which of the following best explains why tertiary alkyl radicals are more stable than primary alkyl radicals?

Accepted Answer

Tertiary radicals are stabilized by hyperconjugation and alkyl group electron donation.

Question 13

A student is asked to propose a synthesis of trans-1,2-dichlorocyclopentane from cyclopentane. Which of the following is the best approach?

Accepted Answer

Chlorinate cyclopentane to form cyclopentene, then add Cl$$_2 to $$the double bond to get the trans-dichloride.

Question 14

Which of the following is a real-world application of free radical chemistry?

Accepted Answer

The synthesis of polyethylene plastics via free-radical polymerization of ethylene.

Question 15

Which of the following best describes the selectivity of chlorination versus bromination in the halogenation of alkanes?

Accepted Answer

Bromination is more selective than chlorination due to the higher activation energy for hydrogen abstraction.

Question 16

In the free-radical addition of HBr to an alkene in the presence of peroxides, which step determines the regioselectivity of the product?

Accepted Answer

Addition of the bromine atom to the alkene, forming the most stable radical intermediate.

Question 17

Which of the following is the correct mechanism for the propagation steps in the free-radical chlorination of methane?

Accepted Answer

$$\mathrm{Cl}^\cdot + \mathrm{CH}_4 \rightarrow \mathrm{CH}_3^\cdot + \mathrm{HCl}$$ followed by $$\mathrm{CH}_3^\cdot + \mathrm{Cl}_2 \rightarrow \mathrm{CH}_3\mathrm{Cl} + \mathrm{Cl}^\cdot$$

Question 18

Which of the following best explains why the addition of HBr to alkenes in the presence of peroxides gives anti-Markovnikov products?

Accepted Answer

The reaction proceeds via a free radical mechanism, where the bromine radical adds to the less substituted carbon to form the more stable radical.

Question 19

Which of the following is NOT a free radical?

Accepted Answer

$$\mathrm{CO}_2$$

Chapter 10: Introduction to Free Radicals and Their Reactions

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