Question 1

Which of the following statements best describes the rate law for an $$S_N1$$ reaction involving an alkyl halide and a nucleophile?

Accepted Answer

Rate $$=$$ $$k[	ext{alkyl halide}]$$

Question 2

During the $$S_N1$$ reaction of $$(S)-1-$$bromopropylbenzene with water, which intermediate is formed after the departure of the leaving group?

Accepted Answer

A carbocation stabilized by resonance with the benzene ring

Question 3

Why does 3-bromopentan-2-one not react with nucleophiles by an $$S_N1$$ mechanism?

Accepted Answer

The resulting carbocation is destabilized by the electron-withdrawing carbonyl group

Question 4

In the $$S_N2$$ reaction of 3-bromopentan-2-one with NaN$$_3$$, what feature of the transition state stabilizes the reaction?

Accepted Answer

Orbital overlap between the nucleophile and the antibonding orbital of the C-Br bond, facilitated by the electron-withdrawing carbonyl group

Question 5

Which of the following best explains why $$S_N1 is $$favored over $$S_N2$$ for the reaction of $$(S)-1-$$bromopropylbenzene with water?

Accepted Answer

The benzylic carbocation intermediate is stabilized by resonance, making $$S_N1$$ favorable

Question 6

In the acid-catalyzed elimination of 2-methyl-2-butanol with H$$_2SO$_4$$, which is the major product and why?

Accepted Answer

2-methyl-2-butene, because it is the more substituted (Zaitsev) alkene

Question 7

When converting a secondary alcohol to an alkyl chloride using SOCl$$_2$$ and pyridine, what is the role of pyridine?

Accepted Answer

It acts as a base to neutralize HCl formed during the reaction

Question 8

Which of the following solvents would be most appropriate for the second step in the conversion of an alkyl chloride to an alkene via elimination?

Accepted Answer

A polar aprotic solvent such as DMSO

Question 9

In the reaction of a secondary alcohol with HBr, what is the expected major product?

Accepted Answer

The corresponding alkyl bromide formed via an $$S_N1$$ mechanism

Question 10

In the acid-catalyzed elimination of 2-methyl-2-butanol, what feature of the energy profile diagram explains the major product distribution?

Accepted Answer

The lower activation energy for formation of the more substituted alkene

Question 11

In a POCl$$_3/$$pyridine-mediated elimination of a secondary alcohol, what is the major product and what selectivity is relevant?

Accepted Answer

The more substituted alkene due to Zaitsev selectivity

Question 12

When using POCl$$_3/$$pyridine to dehydrate diastereomeric alcohols, what determines the stereochemistry of the major alkene product?

Accepted Answer

The anti-periplanar arrangement of the leaving group and hydrogen in the E2 mechanism

Question 13

In the hydroxide-mediated opening of an epoxide, which carbon does the nucleophile attack?

Accepted Answer

The less substituted carbon due to steric and electronic effects

Question 14

What is the relationship between the stereoisomeric products formed in the base-catalyzed opening of a chiral epoxide?

Accepted Answer

They are enantiomers

Question 15

Which of the following best describes the transition state of an $$S_N2$$ reaction?

Accepted Answer

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

Question 16

In the $$S_N1$$ reaction mechanism, which step is rate-determining?

Accepted Answer

Loss of the leaving group to form the carbocation

Question 17

Which of the following is a common misconception about the $$S_N1$$ mechanism?

Accepted Answer

The nucleophile determines the rate of the reaction

Question 18

Which of the following statements about the energy profile of an $$S_N1$$ reaction is correct?

Accepted Answer

There are two energy maxima corresponding to two transition states

Question 19

In the acid-catalyzed elimination of alcohols, what is the role of the acid?

Accepted Answer

It protonates the alcohol to make it a better leaving group

Nucleophilic Substitution and Elimination Reactions: Mechanisms, Energy Profiles, and Stereochemistry

Study Guide - Practice Questions