Question 1

Which factor most strongly stabilizes a benzylic radical compared to a tertiary alkyl radical?

Accepted Answer

Resonance delocalization with the aromatic ring

Question 2

In the radical chlorination of methane, what is the role of light (photon, $$h
u) in $$the initiation step?

Accepted Answer

It breaks the Cl-Cl bond to generate chlorine radicals

Question 3

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

Accepted Answer

Methyl \u003c Primary \u003c Secondary \u003c Tertiary

Question 4

According to the Hammond postulate, the transition state of an exothermic radical halogenation reaction resembles which species?

Accepted Answer

The reactants

Question 5

Why is radical bromination of alkanes more selective than radical chlorination?

Accepted Answer

Bromine radicals are less reactive and the activation energy for H-abstraction is higher, making the transition state more product-like

Question 6

Given the bond dissociation energies: $$\mathrm{Cl-Cl} = 58\ \mathrm{kcal/mol}$$ and $$\mathrm{Br-Br} = 46\ \mathrm{kcal/mol}$$, which halogen is easier to homolytically cleave during radical initiation?

Accepted Answer

Bromine

Question 7

In the radical chlorination of propane, what is the expected major product and why?

Accepted Answer

2-chloropropane, because secondary hydrogens are more reactive and lead to a more stable radical

Question 8

Which propagation step is rate-determining in radical halogenation reactions?

Accepted Answer

First propagation (hydrogen abstraction)

Question 9

What is the effect of hyperconjugation on the stability of alkyl radicals?

Accepted Answer

It stabilizes the radical by delocalizing electrons from adjacent C-H bonds into the empty p orbital

Question 10

A student performs radical bromination of toluene using NBS. What is the major product?

Accepted Answer

Benzyl bromide

Question 11

Which equation best describes the rate constant for a radical halogenation reaction?

Accepted Answer

$$k_r = Ae$$^{-E_a/RT}$$

Question 12

During radical chlorination of propane, the activation energy for abstraction of a secondary hydrogen is lower than for a primary hydrogen. What does this imply about the relative rates?

Accepted Answer

Secondary hydrogens react faster

Question 13

Which termination step is possible in the radical chlorination of methane?

Accepted Answer

Combination of two methyl radicals to form ethane

Question 14

Why is the radical chain reaction for halogenation considered exothermic?

Accepted Answer

The overall enthalpy change $$\Delta H^\circ is $$negative

Question 15

Which of the following best explains the selectivity of bromine in radical halogenation?

Accepted Answer

Bromine reacts more slowly, allowing for greater discrimination between different types of hydrogens

Question 16

In radical polymerization, what is the role of the radical initiator?

Accepted Answer

It generates radicals that start the chain reaction

Question 17

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

Accepted Answer

Both are stabilized by resonance delocalization

Question 18

During the radical halogenation of propane, what is the ratio of reactivity of secondary to primary hydrogens?

Accepted Answer

4.5:1

Question 19

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

Accepted Answer

$$\mathrm{CH_4$} + \mathrm{Cl^\cdot} \rightarrow \mathrm{CH_3$^\cdot} + \mathrm{HCl}$$

Question 20

Which of the following best describes the effect of the transition state structure on selectivity in radical halogenation?

Accepted Answer

A product-like transition state increases selectivity for the most stable radical

Free Radical Halogenation and Organic Radical Chemistry

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