Question 1

Which of the following statements best explains why bromination of isobutane with $$\mathrm{Br_2$}$$ and light gives tert-butyl bromide as the major product?

Accepted Answer

Bromine radicals are less reactive and more selective, favoring the formation of the most stable (tertiary) radical intermediate.

Question 2

In the free radical halogenation of cyclohexane with $$\mathrm{Cl_2$}$$ and light, why is a mixture of products formed?

Accepted Answer

All hydrogens in cyclohexane are equivalent, so chlorination is not selective.

Question 3

Which position is most likely to be brominated in the reaction of cyclohexene with $$\mathrm{Br_2$}$$ and light?

Accepted Answer

The allylic position (carbon adjacent to the double bond)

Question 4

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

Accepted Answer

It maintains a low, steady concentration of $$\mathrm{Br_2$}$$ for selective allylic bromination.

Question 5

Which of the following best describes the mechanism of the $$\mathrm{S_N2}$$ reaction?

Accepted Answer

A concerted, one-step process where the nucleophile attacks as the leaving group departs.

Question 6

Given the reaction: $$\mathrm{CH_3I + OH^- \rightarrow CH_3OH + I^-}$$, what is the rate law for this $$\mathrm{S_N2}$$ reaction?

Accepted Answer

$$\mathrm{rate = k[CH_3I][OH^-]}$$

Question 7

Why are allylic radicals more stable than alkyl radicals?

Accepted Answer

They are stabilized by resonance with the adjacent double bond.

Question 8

Which of the following is a correct statement about the selectivity of halogenation reactions?

Accepted Answer

Bromination is more selective than chlorination, favoring the most substituted carbon.

Question 9

In the $$\mathrm{S_N2}$$ reaction mechanism, what happens to the stereochemistry of the substrate?

Accepted Answer

It is inverted (backside attack).

Question 10

Which of the following best explains why $$\mathrm{S_N2}$$ reactions are faster with methyl and primary alkyl halides than with tertiary alkyl halides?

Accepted Answer

There is less steric hindrance for the nucleophile to attack.

Question 11

A student attempts to brominate cyclohexene using $$\mathrm{Br_2$}$$ and light, but instead of the expected allylic bromide, they obtain a dibromide. What is the most likely reason?

Accepted Answer

Too high a concentration of $$\mathrm{Br_2$}$$ leads to addition across the double bond.

Question 12

Which of the following is NOT a feature of the $$\mathrm{S_N2}$$ reaction mechanism?

Accepted Answer

Formation of a carbocation intermediate.

Question 13

What is the main advantage of using NBS over $$\mathrm{Br_2$} in $$allylic bromination?

Accepted Answer

NBS prevents addition of bromine across the double bond by keeping $$\mathrm{Br_2$}$$ concentration low.

Question 14

Which of the following best describes the transition state in an $$\mathrm{S_N2}$$ reaction?

Accepted Answer

A pentavalent carbon with partial bonds to both the nucleophile and leaving group.

Question 15

In the reaction of 2,3-dimethylbut-2-ene with NBS and light, which product is favored?

Accepted Answer

Allylic bromide at the methyl group adjacent to the double bond.

Question 16

Which of the following is the correct order of reactivity for free radical bromination of alkanes?

Accepted Answer

$$3^\circ \u003e 2^\circ \u003e 1^\circ$$

Question 17

Which of the following best describes the leaving group in an $$\mathrm{S_N2}$$ reaction?

Accepted Answer

It departs with a pair of electrons as the nucleophile attacks.

Question 18

Which of the following is a common misconception about the $$\mathrm{S_N2}$$ reaction?

Accepted Answer

It proceeds faster with tertiary alkyl halides due to increased stability.

Question 19

In the mechanism of allylic bromination, what is the first step?

Accepted Answer

Abstraction of an allylic hydrogen by a bromine radical.

Question 20

Which of the following best explains why $$\mathrm{S_N2}$$ reactions are not suitable for tertiary alkyl halides?

Accepted Answer

Steric hindrance prevents the nucleophile from attacking the carbon center.

Preparation and Reactions of Alkyl Halides: Free Radical Halogenation and SN2 Mechanism

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