Question 1

Which of the following statements best describes the rate-limiting step in the electrophilic addition of HBr to an alkene?

Accepted Answer

The formation of the carbocation intermediate from the alkene and HBr.

Question 2

Why are tertiary carbocations more stable than secondary or primary carbocations?

Accepted Answer

They are stabilized by hyperconjugation and inductive effects from surrounding alkyl groups.

Question 3

In the addition of HCl to 2-methylpropene, which product is formed as the major product and why?

Accepted Answer

tert-Butyl chloride, because the carbocation intermediate is tertiary and more stable.

Question 4

Which of the following best explains why the addition of HBr to 1-butene produces 2-bromobutane as the major product?

Accepted Answer

The reaction forms a more stable secondary carbocation intermediate.

Question 5

What is the outcome when an alkene reacts with water in the presence of a strong acid such as $$\mathrm{H_2SO_4}$$?

Accepted Answer

An alcohol is formed via Markovnikov addition.

Question 6

Which of the following is a potential problem when synthesizing alcohols via acid-catalyzed hydration of alkenes?

Accepted Answer

Carbocation rearrangements can lead to unexpected products.

Question 7

A 1,2-hydride shift occurs during the addition of HBr to certain alkenes. What is the purpose of this rearrangement?

Accepted Answer

To form a more stable carbocation intermediate.

Question 8

Which of the following reactions is NOT regioselective?

Accepted Answer

Addition of HBr to 2-pentene.

Question 9

Which statement best describes a stereoselective reaction?

Accepted Answer

A reaction that forms more of one stereoisomer than another.

Question 10

When an achiral alkene forms a product with a single chiral center via electrophilic addition, what is the expected stereochemical outcome?

Accepted Answer

A racemic mixture is formed.

Question 11

Which of the following best explains why the product of acid-catalyzed hydration of 3-methyl-1-butene is 2-methyl-2-butanol?

Accepted Answer

A 1,2-hydride shift occurs to form a more stable tertiary carbocation.

Question 12

Which of the following is true about the addition of HBr to 2-methyl-2-butene?

Accepted Answer

The reaction forms a tertiary carbocation intermediate, leading to the major product.

Question 13

Which of the following best describes a stereospecific reaction?

Accepted Answer

A reaction in which each stereoisomer of the reactant forms a different stereoisomer of the product.

Question 14

Which of the following is a consequence of the nucleophile attacking the planar carbocation intermediate from either side?

Accepted Answer

A racemic mixture of enantiomers is formed.

Question 15

Which of the following is NOT a feature common to all electrophilic addition reactions of alkenes?

Accepted Answer

A carbocation rearrangement always occurs.

Question 16

Which of the following best describes the product(s) when 1-butene reacts with HBr?

Accepted Answer

2-bromobutane as the major product due to Markovnikov addition.

Question 17

Which of the following is a reason why acid-catalyzed hydration is not always the preferred method for synthesizing alcohols from alkenes?

Accepted Answer

Acidic conditions can cause rearrangements and are harmful to sensitive organic compounds.

Question 18

Which of the following statements about regioselectivity is correct?

Accepted Answer

A regioselective reaction forms more of one constitutional isomer than another.

Question 19

Which of the following is true about the formation of stereoisomers in electrophilic addition reactions?

Accepted Answer

If a product has a chiral center and the reactant does not, a racemic mixture forms.

Electrophilic Addition Reactions of Alkenes: Mechanisms, Regioselectivity, and Stereochemistry

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