Question 1

Which of the following statements best describes the difference between the E1 and E2 elimination mechanisms?

Accepted Answer

E1 elimination proceeds via a two-step mechanism with a carbocation intermediate, while E2 is a single-step, concerted process.

Question 2

Consider the following reaction: $$\mathrm{CH_3CH_2Br} + \mathrm{NaOEt} \rightarrow (in $$ethanol). What is the major product and the mechanism?

Accepted Answer

The major product is ethene, formed via an E2 mechanism.

Question 3

Which of the following conditions would most likely increase the rate of an E2 elimination reaction?

Accepted Answer

Using a strong base and a polar aprotic solvent.

Question 4

A tertiary alcohol is treated with $$\mathrm{H_2SO_4}$$ and heat. What is the expected major product and mechanism?

Accepted Answer

An alkene via an E1 elimination mechanism.

Question 5

Which of the following alkyl halides will react fastest in an SN1 reaction?

Accepted Answer

Tertiary alkyl bromide ($$\mathrm{(CH_3$)_3CBr})$$

Question 6

Which of the following statements about carbocation rearrangement in SN1 reactions is correct?

Accepted Answer

Carbocation rearrangement occurs to form a more stable carbocation, such as tertiary or allylic.

Question 7

Rank the following carbocations from least stable to most stable: $$\mathrm{CH_3$^+}$$, $$\mathrm{CH_3CH_2^+}$$, $$\mathrm{(CH_3$)_2CH^+}$$, $$\mathrm{(CH_3$)_3C^+}.$$

Accepted Answer

$$\mathrm{CH_3$^+} \u003c \mathrm{CH_3CH_2^+} \u003c \mathrm{(CH_3$)_2CH^+} \u003c \mathrm{(CH_3$)_3C^+}$$

Question 8

Which of the following solvents would most likely favor an SN2 reaction mechanism?

Accepted Answer

Dimethyl sulfoxide (DMSO)

Question 9

A chiral alkyl halide undergoes E2 elimination. Which statement about the stereochemistry of the product is correct?

Accepted Answer

The product will be formed only if the leaving group and the hydrogen are anti-periplanar.

Question 10

Which of the following best explains why no elimination is observed in an SN1 reaction of a tertiary alcohol with $$\mathrm{HBr} at $$room temperature?

Accepted Answer

The reaction conditions favor substitution over elimination due to the presence of a strong nucleophile.

Question 11

Which of the following statements about the effect of solvent on SN1 and SN2 reactions is correct?

Accepted Answer

Polar protic solvents favor SN1 reactions by stabilizing the carbocation intermediate.

Question 12

Which of the following reaction conditions would most likely result in a rearrangement during an SN1 reaction?

Accepted Answer

A secondary alkyl halide with a possibility of forming a more stable carbocation.

Question 13

Which of the following is the correct order of stability for the following isomers of hexene (from least to most stable)? $$\mathrm{1-hexene}$$, $$\mathrm{2-hexene} ($$cis), $$\mathrm{2-hexene} ($$trans), $$\mathrm{3-hexene}$$

Accepted Answer

$$\mathrm{1-hexene} \u003c \mathrm{3-hexene} \u003c \mathrm{2-hexene} ($$cis) $$\u003c \mathrm{2-hexene} ($$trans)

Question 14

Which of the following statements about the number of stereoisomers formed in an E1 elimination of a tertiary alcohol is correct?

Accepted Answer

Two stereoisomers are formed due to the possibility of cis and trans alkenes.

Question 15

Which of the following best describes the role of a strong base in an E2 elimination reaction?

Accepted Answer

It abstracts a proton from the beta-carbon, facilitating the elimination.

Question 16

Which of the following reaction conditions would most likely favor an SN2 mechanism over an E2 mechanism?

Accepted Answer

A primary alkyl halide with a strong, non-bulky nucleophile in a polar aprotic solvent.

Question 17

Which of the following is a correct statement about the stereochemistry of the E2 elimination product when the substrate is chiral?

Accepted Answer

The product's stereochemistry depends on the anti-periplanar arrangement of the leaving group and hydrogen.

Question 18

Which of the following is the best explanation for why SN2 reactions are faster with methyl and primary alkyl halides than with tertiary alkyl halides?

Accepted Answer

Methyl and primary alkyl halides have less steric hindrance, allowing easier backside attack.

Substitution and Elimination Reactions in Organic Chemistry: Practice Exam Study Guide

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