Question 1

Which of the following statements best explains why the major product in the addition of HBr to 2-methylpropene in the presence of peroxides is 1-bromopropane rather than 2-bromopropane?

Accepted Answer

The peroxide effect leads to anti-Markovnikov addition, where the Br radical adds to the less substituted carbon to form a more stable radical intermediate.

Question 2

Which of the following is the best description of a nucleophile in organic chemistry?

Accepted Answer

A species that donates a pair of electrons to an electrophile.

Question 3

In the radical bromination of cyclohexene using N-bromosuccinimide (NBS) and light, which position is most likely to be brominated?

Accepted Answer

The allylic position, because the resulting radical is resonance stabilized.

Question 4

Which of the following is a common feature of a good leaving group in nucleophilic substitution reactions?

Accepted Answer

It forms a relatively stable, weak base after departure.

Question 5

Consider the following reaction: $$\mathrm{CH_3CH_2Br} + \mathrm{OH^-} \rightarrow \mathrm{CH_3CH_2OH} + \mathrm{Br^-}. $$Which mechanism is most likely for this reaction?

Accepted Answer

SN2 substitution

Question 6

Why is a tertiary carbocation ($$3^\circ) $$more stable than a secondary or primary carbocation?

Accepted Answer

Because of the inductive and hyperconjugation effects from the surrounding alkyl groups.

Question 7

Which of the following is the best explanation for the anti-Markovnikov addition of HBr to alkenes in the presence of peroxides?

Accepted Answer

The reaction proceeds via a bromine radical, which adds to the less substituted carbon to form the more stable radical intermediate.

Question 8

Which of the following is NOT a common nucleophile in organic reactions?

Accepted Answer

$$\mathrm{BF_3$}$$

Question 9

In an SN1 reaction, which step is rate-determining?

Accepted Answer

Loss of the leaving group to form the carbocation.

Question 10

Which of the following statements about N-bromosuccinimide (NBS) is correct?

Accepted Answer

NBS is an ideal source of low, steady concentrations of Br$$_2$$ for allylic bromination.

Question 11

Which of the following best explains why SN2 reactions are faster with methyl and primary alkyl halides than with tertiary alkyl halides?

Accepted Answer

Steric hindrance is lower in methyl and primary alkyl halides, allowing easier backside attack by the nucleophile.

Question 12

Which of the following is the correct order of carbocation stability?

Accepted Answer

$$3^\circ \u003e 2^\circ \u003e 1^\circ \u003e \mathrm{CH_3$^+}$$

Question 13

A student attempts to brominate cyclohexene using Br$$_2 in $$the dark. What is the most likely product?

Accepted Answer

A vicinal dibromide, with Br atoms added across the double bond.

Question 14

Which of the following best describes the role of peroxides in the addition of HBr to alkenes?

Accepted Answer

They initiate a free radical chain mechanism.

Question 15

Which of the following is a common leaving group in nucleophilic substitution reactions?

Accepted Answer

$$\mathrm{Br^-}$$

Question 16

Which of the following statements about the SN1 and SN2 mechanisms is correct?

Accepted Answer

SN2 reactions proceed with inversion of configuration at the reaction center.

Question 17

Which of the following best explains why the allylic position is especially reactive in radical bromination?

Accepted Answer

The allylic radical is stabilized by resonance.

Question 18

Which of the following is the best example of a nucleophilic substitution reaction?

Accepted Answer

$$\mathrm{CH_3Br} + \mathrm{OH^-} \rightarrow \mathrm{CH_3OH} + \mathrm{Br^-}$$

Question 19

Which of the following is a correct statement about the Markovnikov rule in the addition of HBr to alkenes?

Accepted Answer

The Br atom adds to the more substituted carbon of the double bond.

Alkene Reactions and Nucleophilic Substitution Mechanisms

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