Question 1

Which of the following statements best explains why $$S_N2$$ reactions are faster in polar aprotic solvents than in polar protic solvents?

Accepted Answer

Polar aprotic solvents do not solvate the nucleophile strongly, allowing it to remain highly reactive.

Question 2

Given the following rate law for an $$S_N2$$ reaction: $$	ext{Rate} = k[	ext{alkyl halide}][	ext{nucleophile}]$$, what would happen to the rate if the concentration of the nucleophile is tripled?

Accepted Answer

The rate would increase by a factor of 3.

Question 3

Which substrate would react fastest in an $$S_N2$$ reaction with iodide ion as the nucleophile?

Accepted Answer

Methyl bromide $$(CH_3Br)$$

Question 4

In the energy diagram for the $$S_N2$$ reaction of $$CH_3Cl$$ with hydroxide, the free energy of activation $$(\Delta G$$^{\ddagger}$$) is 103 kJ/$$mol. What is the practical implication of this value for the reaction conditions?

Accepted Answer

The reaction will require heating to proceed at a reasonable rate.

Question 5

Which of the following is the best leaving group for $$S_N2$$ reactions, based on the provided data?

Accepted Answer

$$I^-$$

Question 6

A student attempts an $$S_N2$$ reaction using neopentyl chloride and a strong nucleophile in DMSO. What is the expected outcome?

Accepted Answer

The reaction will be extremely slow due to steric hindrance at the substrate.

Question 7

Which of the following best describes the mechanism of an $$S_N2$$ reaction?

Accepted Answer

A concerted mechanism with simultaneous bond formation and bond breaking.

Question 8

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

Accepted Answer

Formation of the carbocation intermediate.

Question 9

Which of the following statements about $$S_N1$$ and $$S_N2$$ reactions is correct?

Accepted Answer

$$S_N2$$ reactions are favored by strong nucleophiles and polar aprotic solvents.

Question 10

Which of the following would most likely increase the rate of an $$S_N1$$ reaction?

Accepted Answer

Using a polar protic solvent.

Question 11

A reaction of $$(CH_3$)_2CHBr ($$isopropyl bromide) with water can proceed by either $$S_N1 or$$ $$S_N2$$ mechanism. Which condition will favor the $$S_N2$$ pathway?

Accepted Answer

Using a strong nucleophile such as $$OH^- in a $$polar aprotic solvent.

Question 12

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

Accepted Answer

Steric hindrance prevents the nucleophile from attacking the carbon.

Question 13

Which of the following nucleophiles would react fastest in an $$S_N2$$ reaction in a protic solvent?

Accepted Answer

$$I^-$$

Question 14

In an $$S_N1$$ reaction, what is the expected stereochemical outcome if the substrate is chiral?

Accepted Answer

Racemic mixture due to planar carbocation intermediate.

Question 15

Which factor most strongly influences the rate of $$S_N1$$ reactions?

Accepted Answer

Stability of the carbocation intermediate.

Question 16

A chemist wants to increase the rate of an $$S_N2$$ reaction. Which of the following changes would be most effective?

Accepted Answer

Using a less hindered (primary) alkyl halide.

Question 17

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

Accepted Answer

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

Question 18

Why do alkyl iodides react faster than alkyl chlorides in both $$S_N1$$ and $$S_N2$$ reactions?

Accepted Answer

Iodide is a better leaving group due to its larger size and weaker bond to carbon.

Question 19

Which of the following changes will NOT affect the rate of an $$S_N1$$ reaction?

Accepted Answer

Changing the concentration of the nucleophile.

Nucleophilic Substitution Reactions: $S_N2$ and $S_N1$ Mechanisms

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