$$\text{tertiary} \u003e \text{secondary} \u003e \text{primary} \u003e \text{methyl}$$

Question 1

Which of the following best explains why the π bond in an alkene acts as a nucleophile in electrophilic addition reactions?

Accepted Answer

The π bond is electron-rich and can donate electron density to electrophiles.

Question 2

In the hydrohalogenation of propene with HBr, which product is favored and why?

Accepted Answer

2-bromopropane, because the secondary carbocation intermediate is more stable than the primary.

Question 3

Which of the following statements about carbocation stability is correct?

Accepted Answer

Tertiary carbocations are more stable than secondary and primary carbocations due to hyperconjugation and inductive effects.

Question 4

According to Markovnikov’s rule, in the addition of HX to an asymmetric alkene, the hydrogen atom will add to:

Accepted Answer

The carbon with the greater number of hydrogen atoms already attached.

Question 5

Which mechanistic step is typically the rate-determining step in the electrophilic addition of HX to an alkene?

Accepted Answer

Formation of the carbocation intermediate.

Question 6

What is the main reason that resonance stabilization increases carbocation stability?

Accepted Answer

Delocalization of the positive charge over multiple atoms reduces the energy of the carbocation.

Question 7

Which of the following best describes hyperconjugation?

Accepted Answer

Electron donation from adjacent σ bonds to a vacant p orbital on a carbocation.

Question 8

A student proposes that the addition of HCl to 1-butene will produce only 1-chlorobutane. Is this correct? Why or why not?

Accepted Answer

No, because Markovnikov’s rule predicts the major product will be 2-chlorobutane.

Question 9

Which of the following is the correct order of carbocation stability?

Accepted Answer

$$	ext{tertiary} \u003e 	ext{secondary} \u003e 	ext{primary} \u003e 	ext{methyl}$$

Question 10

Which statement about Hammond’s postulate is correct?

Accepted Answer

The transition state of a reaction resembles the species (reactants or products) closest in energy.

Question 11

In the addition of HBr to 3-methyl-1-butene, which carbocation intermediate is most likely to form?

Accepted Answer

A tertiary carbocation, due to greater stability from hyperconjugation.

Question 12

Which of the following best explains why the addition of water to an alkene in the presence of acid follows Markovnikov’s rule?

Accepted Answer

The more stable carbocation intermediate is formed, leading to the major product.

Question 13

Which of the following is NOT a method for stabilizing a carbocation?

Accepted Answer

Increasing the number of electron-withdrawing groups attached to the carbocation.

Question 14

A reaction of cyclohexene with HBr produces a mixture of products. Which mechanistic feature explains this observation?

Accepted Answer

Resonance stabilization of the carbocation intermediate creates multiple reactive sites.

Question 15

Which of the following best describes the role of the halide ion (e.g., Br⁻) in the second step of hydrohalogenation of an alkene?

Accepted Answer

It acts as a nucleophile and attacks the carbocation intermediate.

Question 16

Which of the following is a real-world application of Markovnikov’s rule?

Accepted Answer

The synthesis of pharmaceuticals where regioselective addition of functional groups is required.

Question 17

Which of the following statements about the energy diagram for electrophilic addition to alkenes is correct?

Accepted Answer

The first activation energy is larger than the second, making the formation of the carbocation the rate-determining step.

Question 18

Which of the following best explains why a tertiary carbocation is more stable than a primary carbocation?

Accepted Answer

A tertiary carbocation is stabilized by more hyperconjugation and inductive effects from three alkyl groups.

π-Bonds as Nucleophiles and Electrophilic Addition Reactions of Alkenes

Study Guide - Practice Questions