Q: In the free radical chlorination of methane, which step is considered the initiation step?

$$Cl_2$$ \xrightarrow{\Delta \text{ or } h\nu} Cl\cdot + Cl\cdot$$

Question 1

Which of the following best describes homolytic bond cleavage?

Accepted Answer

Each atom takes one electron from the bond, forming two radicals.

Question 2

In the free radical chlorination of methane, which step is considered the initiation step?

Accepted Answer

$$Cl_2$$ \xrightarrow{\Delta 	ext{ or } h
u} Cl\cdot + Cl\cdot$$

Question 3

Which of the following statements about radical stability is correct?

Accepted Answer

Radical stability increases with increasing alkyl substitution.

Question 4

During the propagation step of free radical halogenation, which of the following reactions occurs?

Accepted Answer

$$CH_3$$\cdot + $$Cl_2$$ \rightarrow CH_3Cl + Cl\cdot$$

Question 5

Which halogen is the most selective in free radical halogenation reactions?

Accepted Answer

Bromine ($$Br_2)$$

Question 6

Given the following relative rates of hydrogen abstraction by chlorine: $$3^\circ : 2^\circ : 1^\circ = 5 : 3.8 : 1$$, what percentage of the product will be formed from secondary hydrogens if there are 2 secondary and 6 primary hydrogens?

Accepted Answer

$$55.9\%$$

Question 7

Which of the following best explains why bromine is more selective than chlorine in free radical halogenation?

Accepted Answer

Bromine radicals are less reactive and favor formation of the most stable radical.

Question 8

In the free radical bromination of cyclopentane, which position will be brominated to give the major product?

Accepted Answer

The most substituted carbon.

Question 9

Which of the following is a termination step in a free radical halogenation mechanism?

Accepted Answer

$$CH_3$$\cdot + $$CH_3$$\cdot \rightarrow $$CH_3$$-$$CH_3$$

Question 10

What is the effect of increasing alkyl substitution on the stability of carbocations and radicals?

Accepted Answer

Both carbocations and radicals become more stable.

Question 11

Which of the following best describes heterolytic bond cleavage?

Accepted Answer

Both electrons from the bond go to one atom, forming ions.

Question 12

In the free radical halogenation of propane with chlorine, which product will be the major one?

Accepted Answer

2-chloropropane

Question 13

Which of the following energy diagrams correctly represents the activation energy for hydrogen abstraction by chlorine radicals from primary, secondary, and tertiary hydrogens?

Accepted Answer

The activation energy is lowest for tertiary hydrogens and highest for primary hydrogens.

Question 14

Which of the following statements about the selectivity of halogenation is correct?

Accepted Answer

Bromine is more selective than chlorine.

Question 15

In a free radical halogenation reaction, what is the role of light ($$h
u) or $$heat ($$\Delta$$)?

Accepted Answer

To initiate the formation of free radicals by homolytic cleavage.

Question 16

Which of the following is NOT a propagation step in the free radical chlorination of methane?

Accepted Answer

$$Cl_2$$ \xrightarrow{\Delta 	ext{ or } h
u} Cl\cdot + Cl\cdot$$

Question 17

Which of the following best explains why tertiary radicals are formed faster than primary radicals in halogenation reactions?

Accepted Answer

Tertiary radicals are more stable due to hyperconjugation and alkyl group electron donation.

Question 18

In the bromination of methylcyclopentane, which product will be the major one?

Accepted Answer

Bromination at the most substituted carbon of the cyclopentane ring.

Question 19

Which of the following is true about the difference between carbocations and carbanions?

Accepted Answer

Carbocations are stabilized by alkyl groups, carbanions are destabilized by alkyl groups.

Free Radical Halogenation and Radical Stability in Organic Chemistry

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