Question 1

Which of the following statements best explains why a tertiary alkyl halide reacts only via elimination under SN2/E2 conditions?

Accepted Answer

Tertiary alkyl halides are too sterically hindered for nucleophilic substitution via the SN2 mechanism.

Question 2

A primary alkyl halide reacts with sodium methoxide in methanol. Which product is favored and why?

Accepted Answer

Substitution is favored because primary alkyl halides are less hindered, allowing the SN2 mechanism to proceed efficiently.

Question 3

Which of the following conditions would most likely increase the percentage of elimination product in a reaction with a secondary alkyl halide?

Accepted Answer

Using a strong, bulky base and increasing the reaction temperature.

Question 4

In the Williamson ether synthesis, which combination of reactants would best minimize elimination side products?

Accepted Answer

A primary alkyl halide and an unhindered alkoxide ion.

Question 5

Why does a bulky base such as tert-butoxide favor elimination over substitution in reactions with alkyl halides?

Accepted Answer

Bulky bases are sterically hindered and cannot easily approach the carbon for substitution, so they abstract a proton instead.

Question 6

Given the reaction: $$\mathrm{CH_3CH_2CH_2Br} + \mathrm{CH_3O^-} \rightarrow (in $$methanol), what is the major product and why?

Accepted Answer

Methyl propyl ether, because the primary alkyl halide favors SN2 substitution.

Question 7

Which of the following best describes the effect of increasing temperature on the competition between substitution and elimination reactions?

Accepted Answer

Higher temperature favors elimination due to a greater $$\Delta S$$^{\ddagger}$$ for the elimination pathway.

Question 8

A secondary alkyl halide reacts with sodium ethoxide in ethanol. What is the expected major product and why?

Accepted Answer

An alkene, because a strong base favors elimination (E2) over substitution (SN2).

Question 9

Which of the following statements is true regarding the use of DBN and DBU in elimination reactions?

Accepted Answer

DBN and DBU are strong, non-nucleophilic bases that favor E2 elimination.

Question 10

In the reaction of 2-bromo-2-methylpropane with sodium ethoxide in ethanol, what is the expected product and why?

Accepted Answer

2-Methylpropene, because tertiary alkyl halides undergo elimination exclusively under SN2/E2 conditions.

Question 11

Which of the following best explains why a weak base favors substitution over elimination in reactions with secondary alkyl halides?

Accepted Answer

A weak base is a better nucleophile than a base, so it attacks the carbon rather than abstracting a proton.

Question 12

Which product is favored when 1-bromo-2-methylpropane reacts with sodium methoxide in methanol, and why?

Accepted Answer

2-Methylpropene, because steric hindrance in the alkyl halide favors elimination.

Question 13

Which of the following is the major product when 1-bromopentane reacts with potassium tert-butoxide in tert-butanol?

Accepted Answer

1-Pentene, because the bulky base favors elimination over substitution.

Question 14

Which of the following best describes the outcome when a secondary alkyl halide reacts with acetate ion in acetic acid?

Accepted Answer

Substitution is favored, producing an ester, because acetate is a weak base and good nucleophile.

Question 15

Which of the following statements is true regarding the competition between SN1 and E1 reactions for tertiary alkyl halides?

Accepted Answer

Both substitution and elimination occur because both proceed via a carbocation intermediate.

Question 16

In the synthesis of butyl propyl ether via the Williamson ether synthesis, which reactant should be the alkyl halide to maximize yield?

Accepted Answer

The more hindered group (butyl) should be provided by the alkyl halide.

Question 17

Which of the following best explains why elimination is favored over substitution at higher temperatures?

Accepted Answer

Elimination has a greater entropy of activation ($$\Delta S$$^{\ddagger}$$), making it more favorable at higher temperatures.

Question 18

Which product is favored when 2-chloropropane reacts with sodium ethoxide in ethanol, and why?

Accepted Answer

Propene, because a strong base favors elimination (E2) over substitution (SN2).

Substitution and Elimination Reactions of Alkyl Halides: Mechanisms, Selectivity, and Synthetic Applications

Study Guide - Practice Questions