Q: Consider the reaction of 2-chloro-2-methylpropane with sodium hydroxide in water. Which of the following best describes the rate law for the formation of the alkene product via the E2 mechanism?

$$\text{Rate} = k[\text{2-chloro-2-methylpropane}][\text{NaOH}]$$

Q: A chemist wants to synthesize 2-methylpropene from tert-butyl bromide. Which set of reaction conditions would maximize the yield of the alkene via the E2 mechanism?

React tert-butyl bromide with sodium ethoxide ($$\text{NaOCH}_2\text{CH}_3) in $$ethanol at elevated temperature.

Question 1

Which of the following statements best explains why E1 elimination is typically a minor pathway compared to SN1 substitution when 2-bromo-2-methylpropane is dissolved in methanol at room temperature?

Accepted Answer

The nucleophile (methanol) is more likely to attack the carbocation than to act as a base, leading to a higher yield of substitution product.

Question 2

Consider the reaction of 2-chloro-2-methylpropane with sodium hydroxide in water. Which of the following best describes the rate law for the formation of the alkene product via the E2 mechanism?

Accepted Answer

$$	ext{Rate} = k[	ext{2-chloro-2-methylpropane}][	ext{NaOH}]$$

Question 3

A chemist wants to synthesize 2-methylpropene from tert-butyl bromide. Which set of reaction conditions would maximize the yield of the alkene via the E2 mechanism?

Accepted Answer

React tert-butyl bromide with sodium ethoxide ($$	ext{NaOCH}_2	ext{CH}_3) in $$ethanol at elevated temperature.

Question 4

Which of the following best explains why the E2 elimination of cis-1-bromo-4-tert-butylcyclohexane is much faster than that of the trans isomer?

Accepted Answer

The cis isomer allows the bromine and a neighboring hydrogen to be anti-periplanar and both axial in the chair conformation.

Question 5

Which of the following combinations would most likely result in an E2 elimination as the major pathway?

Accepted Answer

2-bromopropane with potassium tert-butoxide in tert-butyl alcohol

Question 6

A mixture of (CH$$_3$$)$$_3$$COCH$$_2CH$_3 (30$$%), (CH$$_3$$)$$_3$$COH (60%), and (CH$$_3$$)$$_2C=CH$_2 (10$$%) is obtained when 2-bromo-2-methylpropane is dissolved in aqueous ethanol at 25°C. What is the best explanation for the formation of these three products?

Accepted Answer

The reaction forms a common carbocation intermediate, which can be attacked by either ethanol or water (SN1), or lose a proton to form an alkene (E1).

Question 7

Which of the following statements about the E2 mechanism is correct?

Accepted Answer

The E2 mechanism requires the base and the substrate to be present in the rate-determining step.

Question 8

Which factor would most strongly favor elimination (E2) over substitution (SN2) when reacting a primary haloalkane?

Accepted Answer

Using a strong, bulky base such as potassium tert-butoxide.

Question 9

Which of the following best describes the stereochemical requirement for an efficient E2 elimination?

Accepted Answer

The leaving group and the beta-hydrogen must be anti-periplanar.

Question 10

Which of the following sets of conditions would most likely result in an SN1 reaction as the major pathway?

Accepted Answer

A tertiary haloalkane in water at room temperature.

Question 11

Which of the following is NOT a factor that increases the likelihood of elimination (E2 or E1) over substitution (SN1 or SN2)?

Accepted Answer

Using a weak base in a polar aprotic solvent.

Question 12

Which of the following best explains why tertiary haloalkanes do not undergo SN2 reactions?

Accepted Answer

The central carbon is too sterically hindered for nucleophilic attack.

Question 13

A chemist reacts 1-bromopropane with potassium tert-butoxide in tert-butyl alcohol. Which product will predominate and why?

Accepted Answer

The elimination product via E2, because the base is strong and bulky.

Question 14

Which of the following statements about the competition between SN1, SN2, E1, and E2 mechanisms is correct?

Accepted Answer

A tertiary substrate with a strong base will react exclusively via E2.

Question 15

Which of the following is the best strategy to maximize the yield of substitution (SN2) product when reacting a primary haloalkane?

Accepted Answer

Use a good nucleophile that is a weak base, such as cyanide ion ($$	ext{CN}^-).$$

Question 16

Which of the following best explains why higher temperatures favor elimination (E1 or E2) over substitution (SN1 or SN2)?

Accepted Answer

Elimination reactions have a more positive entropy change ($$\Delta S \u003e 0$$), making them more favorable at higher temperatures.

Question 17

Which of the following is a common feature of both E1 and SN1 mechanisms?

Accepted Answer

Both proceed through a carbocation intermediate.

Question 18

Which of the following reagents would most strongly favor E2 elimination over SN2 substitution when reacting with a secondary haloalkane?

Accepted Answer

Potassium tert-butoxide in tert-butyl alcohol

Question 19

Which of the following statements about lithium diisopropylamide (LDA) is correct?

Accepted Answer

LDA is a strong, non-nucleophilic base that favors elimination (E2) due to its steric bulk.

Question 20

Which of the following best describes the outcome when a secondary haloalkane is reacted with water and methanol at elevated temperature?

Accepted Answer

A mixture of SN1 and E1 products, with substitution usually predominating.

Elimination and Substitution Mechanisms: E1, E2, SN1, and SN2 in Haloalkane Chemistry

Guida di studio - Domande di pratica

Study guide - Flashcard