Q: Which of the following is the correct rate law for an $$S_N2$$ reaction?

$$\text{rate} = k[\text{alkyl halide}][\text{nucleophile}]$$

Question 1

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

Accepted Answer

Tertiary alkyl halides are too sterically hindered for the nucleophile to perform a backside attack.

Question 2

Which of the following is the correct rate law for an $$S_N2$$ reaction?

Accepted Answer

$$	ext{rate} = k[	ext{alkyl halide}][	ext{nucleophile}]$$

Question 3

A student is attempting to carry out an $$S_N1$$ reaction with 2-bromo-2-methylpropane in water. Which of the following best describes the expected stereochemical outcome if the starting material is chiral?

Accepted Answer

The product will be a racemic mixture due to attack from both sides of the planar carbocation.

Question 4

Which of the following nucleophiles would react fastest in an $$S_N2$$ reaction with methyl bromide ($$CH_3Br) in a $$polar aprotic solvent?

Accepted Answer

$$CH_3O^-$$

Question 5

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

Accepted Answer

$$Br^-$$

Question 6

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

Accepted Answer

$$S_N2$$, because the substrate is primary and the nucleophile is strong.

Question 7

Which of the following factors increases the rate of an $$S_N1$$ reaction?

Accepted Answer

Increasing the stability of the carbocation intermediate.

Question 8

A secondary alkyl halide reacts with sodium iodide in acetone. Which mechanism is favored and why?

Accepted Answer

$$S_N2$$, because acetone is a polar aprotic solvent and iodide is a strong nucleophile.

Question 9

Which of the following statements about carbocation rearrangements in $$S_N1$$ reactions is correct?

Accepted Answer

Carbocation rearrangements can involve hydride or methyl shifts to form more stable carbocations.

Question 10

Which of the following best explains why $$I^- is a $$better nucleophile than $$F^- in $$polar protic solvents?

Accepted Answer

$$I^- is $$larger and less solvated, so it is more available to attack the substrate.

Question 11

A chiral secondary alkyl bromide undergoes an $$S_N2$$ reaction with $$CN^- as $$the nucleophile. What is the expected stereochemical outcome?

Accepted Answer

Inversion of configuration.

Question 12

Which of the following solvents would most likely favor an $$S_N1$$ mechanism over an $$S_N2$$ mechanism?

Accepted Answer

Water

Question 13

Which of the following statements about nucleophilicity and basicity is correct?

Accepted Answer

Strong bases are often strong nucleophiles, but not all strong nucleophiles are basic.

Question 14

Which of the following alkyl halides will react fastest in an $$S_N1$$ reaction?

Accepted Answer

tert-butyl chloride ($$t-$$BuCl)

Question 15

A primary alkyl halide is treated with a strong nucleophile in a polar aprotic solvent. Which mechanism is most likely and why?

Accepted Answer

$$S_N2$$, because primary alkyl halides are less hindered and the nucleophile is strong.

Question 16

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

Accepted Answer

The carbon is planar and both the nucleophile and leaving group are partially bonded.

Question 17

Which of the following is a common real-world application of $$S_N2$$ reactions?

Accepted Answer

Preparation of ethers via Williamson ether synthesis.

Question 18

Which of the following statements about the effect of solvent on nucleophilicity is correct?

Accepted Answer

Nucleophilicity increases in polar aprotic solvents because nucleophiles are less solvated.

Question 19

A student attempts to react tert-butyl bromide with sodium methoxide in methanol. Which product and mechanism are most likely?

Accepted Answer

Substitution via $$S_N1 to $$give tert-butyl methyl ether.

Question 20

Which of the following best explains why $$S_N1$$ reactions often result in racemization at a chiral center?

Accepted Answer

The carbocation intermediate is planar, allowing attack from either side.

Nucleophilic Substitution Reactions of Alkyl Halides (SN1 and SN2 Mechanisms)

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