Q: Which of the following is the correct expression for the enthalpy change ($$\Delta H) of a $$radical propagation step?

$$\Delta H = \sum \text{(bonds broken)} - \sum \text{(bonds formed)}$$

Question 1

Which of the following best describes a radical in organic chemistry?

Accepted Answer

An uncharged intermediate with an unpaired electron.

Question 2

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

Accepted Answer

Tertiary radicals are more stable than secondary radicals.

Question 3

In the radical chlorination of methane, which step is responsible for generating the chlorine radicals?

Accepted Answer

Initiation

Question 4

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

Accepted Answer

Bromine radicals are less reactive and the transition state is more product-like, favoring the most stable radical.

Question 5

What is the role of N-bromosuccinimide (NBS) in allylic bromination reactions?

Accepted Answer

It provides a low, steady concentration of Br$$_2 to $$favor allylic bromination over addition to the double bond.

Question 6

Which of the following is the correct expression for the enthalpy change ($$\Delta H) of a $$radical propagation step?

Accepted Answer

$$\Delta H = \sum 	ext{(bonds broken)} - \sum 	ext{(bonds formed)}$$

Question 7

Which of the following is a termination step in a radical chain reaction?

Accepted Answer

$$\mathrm{Cl}^\cdot + \mathrm{CH}_3^\cdot \rightarrow \mathrm{CH}_3\mathrm{Cl}$$

Question 8

In the radical addition of HBr to an alkene in the presence of peroxides (ROOR), what is the major product?

Accepted Answer

The anti-Markovnikov product

Question 9

Which of the following best describes homolytic cleavage?

Accepted Answer

Bond electrons are distributed equally, forming radicals.

Question 10

Which of the following statements about the Hammond Postulate is correct in the context of radical halogenation?

Accepted Answer

The transition state of an exothermic step resembles the reactants more than the products.

Question 11

Which propagation step occurs during the radical chlorination of methane?

Accepted Answer

$$\mathrm{Cl}^\cdot + \mathrm{CH}_4 \rightarrow \mathrm{CH}_3^\cdot + \mathrm{HCl}$$

Question 12

Why does radical bromination of alkanes favor the most substituted carbon?

Accepted Answer

The most substituted radical is the most stable due to hyperconjugation.

Question 13

Which of the following is NOT a feature of a free radical chain reaction?

Accepted Answer

All steps must generate more radicals than they consume.

Question 14

Which of the following best explains why the reaction of alkanes with I$$_2$$ does not proceed via a radical mechanism?

Accepted Answer

$$\Delta H_{rxn}$$ for the propagation step is positive (endothermic).

Question 15

Which of the following is the correct order of C–H bond strengths (from weakest to strongest) for the following types: methyl, primary, secondary, tertiary?

Accepted Answer

Tertiary \u003c Secondary \u003c Primary \u003c Methyl

Question 16

In the NBS bromination of toluene, which position is selectively brominated?

Accepted Answer

The benzylic position

Question 17

Which of the following is a correct statement about the effect of temperature on the selectivity of radical halogenation?

Accepted Answer

Increasing temperature decreases selectivity.

Question 18

Which of the following best describes the product distribution in the radical chlorination of propane?

Accepted Answer

A mixture of 1-chloropropane and 2-chloropropane, with more 2-chloropropane due to the more stable secondary radical.

Question 19

Which of the following is true regarding the use of NBS in radical bromination?

Accepted Answer

NBS is used to maintain a low concentration of Br$$_2$$ and prevent addition to double bonds.

Radical Reactions: Mechanisms, Selectivity, and Applications

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