Question 1

Which of the following statements best explains why alkyl halides are more reactive than aryl halides in nucleophilic substitution reactions?

Accepted Answer

Alkyl halides have an sp\^3 hybridized carbon, which is more accessible to nucleophiles than the sp\^2 carbon in aryl halides.

Question 2

Which factor most directly increases the ability of a halide ion to act as a leaving group in nucleophilic substitution?

Accepted Answer

Low pK\_a of the conjugate acid HX.

Question 3

Consider the following reaction: $$\mathrm{CH_3Br} + OH^- \rightarrow CH_3OH + Br^-. $$Which component acts as the nucleophile?

Accepted Answer

OH\^-

Question 4

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

Accepted Answer

I\^-

Question 5

A student attempts a nucleophilic substitution using an alcohol as the leaving group. The reaction fails. What is the most likely reason?

Accepted Answer

Alcohols are poor leaving groups due to their high pK\_a and strong C–O bond.

Question 6

Which of the following solvents would most likely increase the rate of an S\_N2 reaction?

Accepted Answer

Dimethyl sulfoxide (DMSO)

Question 7

Why does nucleophilicity generally increase down a group in the periodic table for halide ions?

Accepted Answer

Because polarizability increases, making the nucleophile more reactive.

Question 8

Which of the following best describes the rate law for an S\_N2 reaction?

Accepted Answer

Rate = k[substrate][nucleophile]

Question 9

A tertiary alkyl halide reacts with a nucleophile in a polar protic solvent. Which substitution mechanism is most likely?

Accepted Answer

S\_N1, because tertiary carbocations are stabilized and polar protic solvents favor ionization.

Question 10

Which of the following statements about nucleophiles is correct?

Accepted Answer

A negatively charged nucleophile is always stronger than its conjugate acid.

Question 11

Which of the following is a common misconception about leaving groups in nucleophilic substitution?

Accepted Answer

Strong bases are good leaving groups.

Question 12

In a nucleophilic substitution reaction, which combination of substrate and nucleophile would most likely result in a fast S\_N2 reaction?

Accepted Answer

Primary alkyl halide and a strong, unhindered nucleophile.

Question 13

Which of the following best explains why tosylate (OTs) is a good leaving group?

Accepted Answer

Its conjugate acid has a low pK\_a, making the anion stable.

Question 14

Which of the following would decrease the nucleophilicity of a nucleophile without affecting its basicity?

Accepted Answer

Increasing steric hindrance around the nucleophilic atom.

Question 15

Which of the following is NOT required for a nucleophilic substitution reaction to occur?

Accepted Answer

A strong acid catalyst.

Question 16

Which of the following best describes the role of the halogen atom in an alkyl halide during nucleophilic substitution?

Accepted Answer

It acts as the leaving group.

Question 17

A chemist wants to convert an alcohol into a better leaving group for nucleophilic substitution. Which reagent would be most effective?

Accepted Answer

Tosyl chloride (TsCl)

Question 18

Which of the following is a real-world application of alkyl halides?

Accepted Answer

They are used as alkylating agents in organic synthesis and as materials such as Teflon and PVC.

Question 19

Which of the following best explains why S\_N2 reactions are faster in polar aprotic solvents than in polar protic solvents?

Accepted Answer

Polar protic solvents form hydrogen bonds with nucleophiles, decreasing their reactivity.

Alkyl Halides & Nucleophilic Substitution: Key Concepts and Mechanisms

Study Guide - Practice Questions