Question 1

Which of the following statements best explains the peroxide effect in the addition of HBr to alkenes?

Accepted Answer

Peroxides reverse the regioselectivity, causing bromine to add to the less substituted carbon due to the stability of the resulting radical.

Question 2

Which arrow notation is used to represent the movement of a single electron in a homolytic bond cleavage?

Accepted Answer

Fishhook arrow

Question 3

What is the correct order of the three steps in a free-radical chain reaction?

Accepted Answer

Initiation, Propagation, Termination

Question 4

Why is propagation more likely than termination in free-radical chain reactions?

Accepted Answer

Free-radical intermediates are present in very low concentrations, making their collisions rare.

Question 5

Which of the following best describes the trend in free-radical stability?

Accepted Answer

Tertiary \u003e Secondary \u003e Primary

Question 6

What is the main difference between electrophilic and radical addition of HBr to an alkene?

Accepted Answer

Electrophilic addition adds a proton first to give the more stable carbocation, while radical addition adds bromine first to give the more stable carbon radical.

Question 7

Which equation correctly defines the bond-dissociation energy (BDE)?

Accepted Answer

$$X-Y \rightarrow X^\cdot + Y^\cdot$$

Question 8

Why is the peroxide effect not observed with HI?

Accepted Answer

The propagation steps for HI are energetically unfavorable because $$\Delta H^\circ is $$positive.

Question 9

Which reagent and conditions are used to convert internal alkynes into trans alkenes?

Accepted Answer

Na in liquid $$NH_3$$

Question 10

During the free-radical polymerization of ethylene, what is the role of the initiator?

Accepted Answer

It provides the radical that starts the chain reaction.

Question 11

Which of the following best describes an isotactic polymer?

Accepted Answer

All substituents are on the same side of the polymer chain.

Question 12

What is the major product when isobutane reacts with Br$$_2$$ under free-radical conditions?

Accepted Answer

tert-Butyl bromide

Question 13

Why is bromination of alkanes more selective than chlorination?

Accepted Answer

Bromine is less reactive, so the transition state resembles the radical intermediate, favoring the more stable radical.

Question 14

Which of the following is a propagation step in the free-radical halogenation of methane?

Accepted Answer

$$Cl^\cdot + CH_4$ \rightarrow HCl + CH_3$^\cdot$$

Question 15

Which of the following best describes the product distribution when methane is treated with excess chlorine under free-radical conditions?

Accepted Answer

A mixture of methyl chloride, methylene chloride, chloroform, and carbon tetrachloride is formed.

Question 16

Which of the following is NOT a characteristic of free-radical polymerization?

Accepted Answer

It always produces isotactic polymers.

Question 17

What is the main reason that trans alkenes are favored in the reduction of alkynes with sodium in liquid ammonia?

Accepted Answer

Trans radicals are more stable due to reduced steric repulsion between R groups.

Question 18

Which of the following best describes the effect of steric hindrance in the peroxide effect mechanism?

Accepted Answer

Steric hindrance favors the formation of tertiary radicals because they are less crowded in the transition state.

Free-Radical Reactions: Mechanisms, Polymerization, and Alkane Halogenation

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