Question 1

Which of the following statements best explains why tertiary alkyl halides do not undergo $$\mathrm{S_N2}$$ reactions efficiently?

Accepted Answer

Tertiary alkyl halides experience significant steric hindrance, preventing nucleophilic backside attack required for $$\mathrm{S_N2}.$$

Question 2

Which factor increases the nucleophilicity of a species in $$\mathrm{S_N2}$$ reactions?

Accepted Answer

Greater negative charge on the nucleophile.

Question 3

Consider the following nucleophiles: $$\mathrm{CH_3O^-}$$, $$\mathrm{CH_3CO_2^-}$$, $$\mathrm{NH_2$^-}$$, and $$\mathrm{tBuO^-}. $$Which is the best nucleophile for $$\mathrm{S_N2}$$ reactions and why?

Accepted Answer

$$\mathrm{CH_3O^-}$$, because it is small, negatively charged, and not sterically hindered.

Question 4

Which of the following alkyl halides will react fastest in an $$\mathrm{S_N2}$$ reaction with $$\mathrm{CH_3O^-} as $$the nucleophile?

Accepted Answer

1-bromopropane

Question 5

Why does the rate law for $$\mathrm{S_N2}$$ reactions depend on both the concentration of the substrate and the nucleophile?

Accepted Answer

Because the nucleophile and substrate react together in a single, concerted step.

Question 6

Which of the following best describes the stereochemical outcome of an $$\mathrm{S_N2}$$ reaction?

Accepted Answer

Inversion of configuration at the reactive carbon.

Question 7

A primary alkyl halide with a gauche methyl neighbor reacts with a nucleophile in an $$\mathrm{S_N2}$$ reaction. How does the presence of the gauche neighbor affect the reaction rate?

Accepted Answer

It decreases the rate by introducing steric hindrance to nucleophilic attack.

Question 8

Which of the following is a poor nucleophile due to its small size and high electronegativity?

Accepted Answer

$$\mathrm{H_2O}$$

Question 9

In an $$\mathrm{S_N1}$$ reaction, which step is rate-determining?

Accepted Answer

Loss of the leaving group to form the carbocation.

Question 10

Which of the following statements about $$\mathrm{S_N1}$$ and $$\mathrm{E1}$$ reactions is correct?

Accepted Answer

The rate law for both is $$r = k[\mathrm{R-X}]$$ and does not depend on nucleophile concentration.

Question 11

Which leaving group order is preferred for $$\mathrm{S_N1}$$ reactions?

Accepted Answer

$$\mathrm{I^-} \u003e \mathrm{Br^-} \u003e \mathrm{Cl^-}$$

Question 12

Which of the following best explains why $$\mathrm{E2}$$ reactions require an anti-periplanar arrangement of the leaving group and the hydrogen being abstracted?

Accepted Answer

It allows for maximum overlap of orbitals during the concerted bond-breaking and bond-forming process.

Question 13

Which product is favored in an $$\mathrm{E1}$$ elimination reaction involving a substrate with multiple different alkyl groups?

Accepted Answer

The most substituted alkene (Zaitsev product).

Question 14

Which of the following bases is considered a strong, non-nucleophilic base and is commonly used to favor $$\mathrm{E2}$$ elimination over substitution?

Accepted Answer

$$\mathrm{LDA} ($$Lithium diisopropylamide)

Question 15

Which of the following statements about the stereochemistry of $$\mathrm{E2}$$ eliminations in cyclohexane derivatives is correct?

Accepted Answer

Elimination is fastest when the leaving group and the hydrogen are both axial and anti-periplanar.

Question 16

A substrate with only one equivalent $$\alpha-$$hydrogen can form how many diastereomeric alkenes in an $$\mathrm{E2}$$ reaction?

Accepted Answer

Only one diastereomer.

Question 17

Which of the following is most likely to undergo a Hofmann elimination ($$\mathrm{E2}) to $$give the least substituted alkene as the major product?

Accepted Answer

A substrate with a bulky base and a bulky leaving group.

Question 18

Which of the following best describes the relationship between $$\mathrm{S_N1}$$ and $$\mathrm{E1}$$ reactions for a tertiary alkyl halide in water?

Accepted Answer

They compete and occur simultaneously, producing a mixture of substitution and elimination products.

Nucleophilic Substitution and Elimination Reactions: Mechanisms, Factors, and Product Prediction

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