Q: Which of the following is required for the initiation step in the radical halogenation of alkanes?

Light ($$h\nu) or $$heat ($$\Delta)$$

Question 1

Which of the following statements best describes the difference between homolytic and heterolytic bond cleavage?

Accepted Answer

Homolytic cleavage results in two radicals, each atom taking one electron, while heterolytic cleavage results in ions, with both electrons going to one atom.

Question 2

What is the hybridization and geometry of a carbon-centered radical?

Accepted Answer

sp2 hybridized, trigonal planar

Question 3

Which of the following radicals is the most stable?

Accepted Answer

Tertiary alkyl radical ($$\mathrm{R_3C\cdot})$$

Question 4

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

Accepted Answer

Tertiary radicals are stabilized by hyperconjugation and inductive effects from surrounding alkyl groups.

Question 5

Which of the following is required for the initiation step in the radical halogenation of alkanes?

Accepted Answer

Light ($$h
u) or $$heat ($$\Delta)$$

Question 6

In the radical halogenation of methane with chlorine, which step is rate-determining?

Accepted Answer

Propagation step 1 (abstraction of H atom to form carbon radical)

Question 7

Why does radical halogenation with $$\mathrm{Cl_2$} or$$ $$\mathrm{Br_2$}$$ often produce a mixture of products when applied to alkanes with different types of hydrogens?

Accepted Answer

Because $$\mathrm{Cl_2$}$$ and $$\mathrm{Br_2$}$$ react with every type of hydrogen present, leading to multiple possible alkyl halide products.

Question 8

Which of the following best describes the role of a radical initiator such as a peroxide ($$\mathrm{ROOR}) in $$radical reactions?

Accepted Answer

It provides a weak bond that homolyzes to generate radicals, starting the chain reaction.

Question 9

Which of the following statements about the termination step in radical halogenation is correct?

Accepted Answer

Termination involves the combination of two radicals to form a stable bond, often resulting in side-products.

Question 10

Consider the following reaction: $$\mathrm{CH_3CH_2CH_3 + Cl_2$ \xrightarrow{h
u} CH_3CHClCH_3 + HCl}. $$Which hydrogen is most likely to be abstracted in the propagation step?

Accepted Answer

A hydrogen from the secondary carbon ($$\mathrm{CH})$$

Question 11

Which of the following best explains why weaker C–H bonds are more readily halogenated in radical reactions?

Accepted Answer

Weaker C–H bonds require less energy to break, making hydrogen abstraction easier.

Question 12

Which of the following is a correct representation of the propagation steps in the radical halogenation of methane with chlorine?

Accepted Answer

$$\mathrm{CH_4$ + Cl\cdot ightarrow CH_3$\cdot + HCl}$$ 
 $$\mathrm{CH_3$\cdot + Cl_2$ ightarrow CH_3Cl + Cl\cdot}$$

Question 13

In the energy diagram for the radical halogenation of ethane, what does the first energy barrier (Ea[1]) correspond to?

Accepted Answer

The energy required for the abstraction of a hydrogen atom by a chlorine radical.

Question 14

Which of the following best describes why radical halogenation is considered a chain reaction?

Accepted Answer

Because each propagation step generates a new radical that continues the reaction sequence.

Question 15

Which of the following is NOT a possible outcome of the termination step in a radical halogenation reaction?

Accepted Answer

Formation of an alkyl halide.

Question 16

Which of the following best explains why peroxide ($$\mathrm{ROOR}) is an $$effective radical initiator?

Accepted Answer

It has a weak O–O bond that readily undergoes homolysis to generate radicals.

Question 17

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

Accepted Answer

Synthesis of polyethylene plastics from ethylene monomers.

Question 18

Which of the following best describes the effect of increasing alkyl substitution on radical stability?

Accepted Answer

Increasing alkyl substitution increases radical stability due to hyperconjugation.

Question 19

Which of the following is true regarding the rearrangement of radicals during halogenation?

Accepted Answer

Secondary and primary radicals do NOT undergo rearrangement.

Radical Reactions in Organic Chemistry: Structure, Stability, and Halogenation Mechanisms

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