Q: Which of the following is the correct order of stability for carbon radicals?

$$3^\circ \u003e 2^\circ \u003e 1^\circ \u003e \text{methyl}$$

Question 1

Which of the following statements best explains why bromination is more selective than chlorination in free radical halogenation of alkanes?

Accepted Answer

Bromine radicals are less reactive and have a higher activation energy, favoring formation of the most stable radical.

Question 2

During the free radical chlorination of propane, the expected ratio of products based on the number of hydrogens is 2:6 (25%:75%), but the actual ratio is closer to 45%:55%. What does this indicate about the reactivity of the hydrogens?

Accepted Answer

Secondary hydrogens are more reactive than primary hydrogens.

Question 3

Which of the following is the correct order of stability for carbon radicals?

Accepted Answer

$$3^\circ \u003e 2^\circ \u003e 1^\circ \u003e 	ext{methyl}$$

Question 4

Why is free radical iodination of alkanes not practical?

Accepted Answer

The first step of the mechanism is endothermic and not favorable.

Question 5

Which reagent is commonly used to generate bromine radicals for allylic bromination in the presence of light or peroxide?

Accepted Answer

N-Bromosuccinimide (NBS)

Question 6

In the free radical addition of HBr to an alkene in the presence of peroxides, which product is favored?

Accepted Answer

Anti-Markovnikov product, where Br adds to the less substituted carbon

Question 7

Which of the following is a common impurity in old bottles of ethers and alkenes that can initiate free radical reactions?

Accepted Answer

Hydroperoxides ($$ROOH)$$

Question 8

What is the main safety concern with storing ethereal solvents for long periods?

Accepted Answer

Formation of peroxides that can detonate

Question 9

Which of the following is a commonly used radical initiator in organic synthesis and acne treatment?

Accepted Answer

Benzoyl peroxide

Question 10

Why does the free-radical mechanism for HBr addition to alkenes require the presence of peroxides?

Accepted Answer

Peroxides generate radicals that initiate the chain reaction.

Question 11

Which of the following statements about the stability of benzylic radicals is correct?

Accepted Answer

Benzylic radicals are more stable than tertiary alkyl radicals due to resonance stabilization.

Question 12

Which of the following best describes the difference between the properties of carbon cations, radicals, and anions?

Accepted Answer

Carbon cations are electron poor and rearrange; radicals are less electron poor and do not rearrange; anions are electron rich and do not rearrange.

Question 13

Which of the following is true about the activation energy in kinetic vs. thermodynamic control of a reaction?

Accepted Answer

Kinetic products form faster due to lower activation energy, while thermodynamic products are more stable but may require higher activation energy.

Question 14

Which of the following is a reason why mineral oil is more shelf-stable than vegetable oil?

Accepted Answer

Mineral oil is composed of saturated alkanes, which are less susceptible to radical cross-linking.

Question 15

In the free radical halogenation of isobutane, which product is favored in bromination?

Accepted Answer

Tertiary bromide

Question 16

Which of the following is a correct description of the propagation step in free radical chlorination?

Accepted Answer

A chlorine radical abstracts a hydrogen atom from the alkane, forming HCl and an alkyl radical.

Question 17

Which of the following is a reason why free radical polymerization is important in industry?

Accepted Answer

It allows the production of addition polymers such as polyethylene and polystyrene.

Question 18

Which of the following statements about the use of NBS in allylic bromination is correct?

Accepted Answer

NBS provides a low, steady concentration of Br$$_2$$ for selective allylic bromination.

Question 19

Which of the following is a correct statement about the termination step in a free radical chain reaction?

Accepted Answer

Two radicals combine to form a stable molecule, ending the chain reaction.

Unit 13: More Radical Chemistry – Free Radical Reactions in Organic Chemistry

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