Question 1

Which of the following statements best explains why tertiary haloalkanes generally undergo SN1 reactions rather than SN2 reactions?

Accepted Answer

Tertiary haloalkanes form stable carbocations and are sterically hindered, preventing backside attack.

Question 2

Consider the reaction: $$\mathrm{CH_3Br} + OH^- \rightarrow CH_3OH + Br^-. $$Which mechanism does this reaction most likely follow and why?

Accepted Answer

SN2, because methyl halides are unhindered and favor bimolecular attack.

Question 3

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

Accepted Answer

$$\mathrm{I^-}$$

Question 4

A reaction is carried out with 2-bromopropane and sodium ethoxide in ethanol. Which product will be the major one, and what rule explains this?

Accepted Answer

Propene, due to Zaitsev's rule favoring the most substituted alkene.

Question 5

Which solvent would most increase the rate of an SN2 reaction involving a negatively charged nucleophile?

Accepted Answer

Acetonitrile

Question 6

What is the stereochemical outcome of an SN2 reaction at a chiral center?

Accepted Answer

Inversion of configuration

Question 7

Which of the following nucleophiles is considered 'good' for nucleophilic substitution reactions?

Accepted Answer

$$\mathrm{HO^-}$$

Question 8

A reaction of tert-butyl bromide with methanol proceeds with which kinetic order and why?

Accepted Answer

First order, because only tert-butyl bromide is involved in the rate-determining step.

Question 9

Which of the following best describes the effect of a polar protic solvent on an SN1 reaction?

Accepted Answer

It increases the rate by stabilizing the carbocation and leaving group.

Question 10

Which of the following statements about E2 reactions is correct?

Accepted Answer

E2 reactions require a strong base and occur in a single concerted step.

Question 11

Which of the following factors most strongly favors an E2 mechanism over an SN2 mechanism?

Accepted Answer

A strong, bulky base such as $$\mathrm{t-BuO^-}$$

Question 12

Which of the following best explains why 1° allylic and benzylic carbocations are more stable than 1° alkyl carbocations?

Accepted Answer

They are stabilized by resonance delocalization.

Question 13

In the reaction of 2-iodooctane with $$^{131}I in $$acetone, what is the stereochemical outcome and what does it indicate about the mechanism?

Accepted Answer

Inversion of configuration, indicating an SN2 mechanism.

Question 14

Which of the following changes will increase the rate of an SN2 reaction between bromoethane and hydroxide ion?

Accepted Answer

Using a polar aprotic solvent such as DMSO

Question 15

Which product is favored in the E2 elimination of 2-bromo-2-methylbutane with sodium ethoxide in ethanol, and why?

Accepted Answer

2-methyl-2-butene, because it is the more substituted alkene (Zaitsev's rule).

Question 16

Which of the following statements about the competition between substitution and elimination is correct?

Accepted Answer

Strong bases with pKa \u003e 11 favor elimination (E2) over substitution (SN2).

Question 17

Which of the following is a key difference between SN1 and SN2 mechanisms?

Accepted Answer

SN1 reactions can undergo skeletal rearrangement, while SN2 reactions do not.

Question 18

Which of the following best describes the effect of branching at the α- or β-carbon on SN2 and E2 reactions?

Accepted Answer

Branching retards SN2 and accelerates E2.

Question 19

Which of the following is the correct order of increasing nucleophilicity for halide ions in polar aprotic solvents?

Accepted Answer

$$\mathrm{I^- \u003c Br^- \u003c Cl^- \u003c F^-}$$

Nucleophilic Substitution and β-Elimination: Mechanisms, Factors, and Applications

Guida di studio - Domande di pratica