Question 1

Which of the following statements best describes the rate law for an $$S_N2$$ reaction involving an alkyl halide and a nucleophile?

Accepted Answer

The rate is second order overall: first order in alkyl halide and first order in nucleophile.

Question 2

A student performs an $$S_N2$$ reaction using 1-bromobutane and sodium cyanide in DMSO. Which product is expected?

Accepted Answer

Butanenitrile ($$CH_3CH_2CH_2CH_2CN)$$

Question 3

Which of the following alkyl halides is LEAST reactive in an $$S_N2$$ reaction?

Accepted Answer

Neopentyl bromide

Question 4

What effect does increasing the concentration of the nucleophile have on the rate of an $$S_N2$$ reaction?

Accepted Answer

It increases the rate.

Question 5

Which of the following is a poor leaving group in nucleophilic substitution reactions?

Accepted Answer

Hydroxide ($$HO^-)$$

Question 6

Why do polar aprotic solvents such as DMSO increase the rate of $$S_N2$$ reactions?

Accepted Answer

They solvate cations but leave nucleophilic anions free to attack.

Question 7

Which of the following statements about $$S_N1$$ reactions is TRUE?

Accepted Answer

The rate depends only on the concentration of the alkyl halide.

Question 8

A tertiary alkyl halide reacts with water to form an alcohol. Which mechanism is most likely?

Accepted Answer

$$S_N1$$

Question 9

Which factor most strongly favors the $$S_N1$$ mechanism over $$S_N2$$?

Accepted Answer

A highly substituted (tertiary) alkyl halide

Question 10

According to Zaitsev’s rule, which product is favored in an E2 elimination of 2-bromobutane?

Accepted Answer

2-butene

Question 11

Which geometric arrangement is required for an E2 elimination to occur efficiently?

Accepted Answer

Anti-periplanar

Question 12

Which of the following statements about the effect of solvent on $$S_N1$$ reactions is correct?

Accepted Answer

Polar solvents stabilize the carbocation intermediate and increase the reaction rate.

Question 13

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

Accepted Answer

Iodide ($$I^-)$$

Question 14

A cyclohexane derivative undergoes E2 elimination. Which hydrogen must be abstracted for the reaction to proceed?

Accepted Answer

A hydrogen trans-diaxial to the leaving group

Question 15

Which of the following nucleophiles is most reactive in $$S_N2$$ reactions under basic conditions?

Accepted Answer

$$I^-$$

Question 16

Which of the following statements about E1 and E2 eliminations is correct?

Accepted Answer

E2 elimination occurs in a single concerted step.

Question 17

In a biological methylation reaction, which molecule typically acts as the methyl donor?

Accepted Answer

S-adenosylmethionine (SAM)

Question 18

Which of the following best explains why alcohols do not typically undergo $$S_N2$$ reactions directly?

Accepted Answer

The hydroxide group ($$HO^-) is a $$poor leaving group.

Question 19

Which of the following is a common biological elimination reaction product formed from a $$eta-$$hydroxy thioester?

Accepted Answer

An unsaturated fatty acid (alkene)

Question 20

Which of the following statements about the transition state of an $$S_N2$$ reaction is correct?

Accepted Answer

It involves partial bonds between the nucleophile and the carbon, and between the carbon and the leaving group.

Reactions of Alkyl Halides: Nucleophilic Substitution and Elimination

Study Guide - Practice Questions