Question 1

Which of the following statements best explains why tertiary alkyl halides react faster via the $$S_N1$$ mechanism than primary alkyl halides?

Accepted Answer

Tertiary alkyl halides form more stable carbocations due to hyperconjugation and inductive effects from alkyl groups.

Question 2

A reaction between 2-bromopropane and sodium hydroxide in ethanol produces a racemic mixture of products. Which mechanism is most likely?

Accepted Answer

$$S_N1$$ mechanism, because the reaction forms a planar carbocation intermediate allowing attack from either face.

Question 3

Which of the following best describes the effect of polar protic solvents on $$S_N2$$ reactions?

Accepted Answer

They decrease the rate by solvating the nucleophile, making it less reactive.

Question 4

Which of the following nucleophiles would react fastest with methyl bromide ($$CH_3Br) in $$dimethyl sulfoxide (DMSO)?

Accepted Answer

$$HO^-$$

Question 5

Why does the reaction of 1-bromobutane with sodium methoxide in DMSO proceed via an $$S_N2$$ mechanism?

Accepted Answer

Because the primary substrate is unhindered and the strong nucleophile can attack directly.

Question 6

Which of the following statements about the stereochemical outcome of $$S_N2$$ reactions is correct?

Accepted Answer

$$S_N2$$ reactions result in inversion of configuration at the carbon center.

Question 7

Which of the following is the best leaving group for nucleophilic substitution reactions?

Accepted Answer

$$H_2O$$

Question 8

A chemist wants to convert an alcohol into a good leaving group for an $$S_N2$$ reaction. Which reagent would be most effective?

Accepted Answer

Tosyl chloride ($$TsCl) in $$pyridine

Question 9

Which of the following statements best explains why benzyl bromide reacts rapidly in $$S_N1$$ reactions?

Accepted Answer

The benzyl carbocation is stabilized by resonance with the aromatic ring.

Question 10

Which product is favored in an E2 elimination of 2-bromopentane with sodium ethoxide, and why?

Accepted Answer

The more substituted alkene, due to Zaitsev's rule.

Question 11

Which of the following best describes the regioselectivity observed in the acid-catalyzed opening of an epoxide?

Accepted Answer

Nucleophilic attack occurs at the most substituted carbon due to carbocation-like character.

Question 12

Which of the following substituents on a benzene ring will activate the ring and direct new substituents to the ortho and para positions?

Accepted Answer

$$OH$$

Question 13

A chemist treats cyclohexanol with $$HBr. $$What is the first step in the mechanism?

Accepted Answer

Protonation of the alcohol to make a better leaving group.

Question 14

Which of the following is a consequence of using a bulky base such as tert-butoxide in an E2 elimination?

Accepted Answer

The Hofmann product (less substituted alkene) is favored due to steric hindrance.

Question 15

Which of the following best explains why $$S_N2$$ reactions do not occur with tertiary alkyl halides?

Accepted Answer

Steric hindrance prevents the nucleophile from attacking the electrophilic carbon.

Question 16

Which of the following statements about electrophilic aromatic substitution is correct?

Accepted Answer

Aromatic rings undergo substitution reactions to retain aromaticity.

Question 17

Which of the following is true regarding the effect of electron-withdrawing groups (EWGs) on electrophilic aromatic substitution?

Accepted Answer

EWGs deactivate the ring and direct substitution to the meta position.

Question 18

Which of the following best describes the stereochemical outcome of bromination of an alkene?

Accepted Answer

Anti addition, bromines add to opposite faces due to the bromonium ion intermediate.

Question 19

Which of the following statements about the Mitsunobu reaction is correct?

Accepted Answer

It converts alcohols into good leaving groups and results in inversion of configuration.

Nucleophilic Substitution and Elimination Reactions: Mechanisms, Factors, and Applications

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