$$\text{Rate} = k[\mathrm{CH_3Br}][\mathrm{OH^-}]$$

Question 1

Which of the following statements best describes the stereochemical outcome of an $$\mathrm{S_N2}$$ reaction at a chiral center?

Accepted Answer

The configuration is inverted at the chiral center.

Question 2

In an $$\mathrm{S_N1}$$ reaction, which of the following factors most strongly influences the rate of the reaction?

Accepted Answer

Stability of the carbocation intermediate

Question 3

Which of the following is the best leaving group for both $$\mathrm{S_N1}$$ and $$\mathrm{S_N2}$$ reactions?

Accepted Answer

$$\mathrm{I^-}$$

Question 4

A student attempts an $$\mathrm{S_N2}$$ reaction using tert-butyl bromide and sodium methoxide in DMSO. What is the most likely outcome?

Accepted Answer

The reaction is very slow or does not occur due to steric hindrance.

Question 5

Which solvent would most likely accelerate an $$\mathrm{S_N1}$$ reaction?

Accepted Answer

Water

Question 6

What is the rate law for an $$\mathrm{S_N2}$$ reaction between $$\mathrm{CH_3Br}$$ and $$\mathrm{OH^-}$$?

Accepted Answer

$$	ext{Rate} = k[\mathrm{CH_3Br}][\mathrm{OH^-}]$$

Question 7

Which of the following best explains why polar aprotic solvents favor $$\mathrm{S_N2}$$ reactions?

Accepted Answer

They solvate cations but not anions, leaving the nucleophile 'naked' and more reactive.

Question 8

A reaction produces a racemic mixture of enantiomers. Which mechanism is most likely responsible?

Accepted Answer

$$\mathrm{S_N1}$$

Question 9

Which of the following alkyl halides will react fastest in an $$\mathrm{S_N1}$$ reaction?

Accepted Answer

tert-butyl bromide

Question 10

What is the main reason that $$\mathrm{OH^-} is a $$poor leaving group in nucleophilic substitution reactions?

Accepted Answer

It is a strong base and forms an unstable anion.

Question 11

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

Accepted Answer

The nucleophile and leaving group are both partially bonded to the substrate carbon.

Question 12

Which of the following nucleophiles would be most effective in an $$\mathrm{S_N2}$$ reaction in DMSO?

Accepted Answer

$$\mathrm{CH_3O^-}$$

Question 13

A chemist wants to maximize the rate of an $$\mathrm{S_N2}$$ reaction. Which combination of substrate and solvent should they choose?

Accepted Answer

Primary alkyl halide in DMSO

Question 14

Which of the following statements about the rate-determining step (r.d.s.) in an $$\mathrm{S_N1}$$ reaction is correct?

Accepted Answer

It is the loss of the leaving group to form a carbocation.

Question 15

Which of the following best explains why $$\mathrm{S_N1}$$ reactions are faster in polar protic solvents?

Accepted Answer

Polar protic solvents stabilize the carbocation and transition state.

Question 16

Which of the following is a key difference between $$\mathrm{S_N1}$$ and $$\mathrm{S_N2}$$ mechanisms?

Accepted Answer

$$\mathrm{S_N1}$$ reactions involve a carbocation intermediate, while $$\mathrm{S_N2}$$ reactions do not.

Question 17

A reaction of 2-bromopropane with water produces a racemic mixture of alcohols. Which mechanism is most likely?

Accepted Answer

$$\mathrm{S_N1}$$

Question 18

Which of the following best describes the effect of resonance on carbocation stability?

Accepted Answer

Resonance stabilizes carbocations by delocalizing positive charge.

Question 19

Which of the following statements is true regarding the nucleophile in an $$\mathrm{S_N2}$$ reaction?

Accepted Answer

The nucleophile attacks from the side opposite the leaving group.

Question 20

Which of the following best explains why methyl halides react faster than tertiary halides in $$\mathrm{S_N2}$$ reactions?

Accepted Answer

Methyl halides are less sterically hindered, allowing easier nucleophilic attack.

Nucleophilic Substitution: SN1 and SN2 Mechanisms

Study Guide - Practice Questions