Question 1

The image shows a pi bond in an alkene being attacked by an electrophile (E+). Which statement best explains why the pi bond is reactive toward electrophiles?

Accepted Answer

The electrons in the pi bond are loosely held and can easily interact with electrophiles.

Question 2

Which of the following best describes the first step in the electrophilic addition of HBr to an alkene?

Accepted Answer

The pi bond attacks the proton (H+) from HBr, forming the most stable carbocation.

Question 3

According to Markovnikov’s rule, when HCl is added to propene, where does the chlorine atom end up?

Accepted Answer

On the carbon with the fewer number of hydrogens.

Question 4

Which of the following statements about carbocation rearrangements during electrophilic addition is correct?

Accepted Answer

Carbocation rearrangements can occur to form a more stable carbocation, such as by a methyl or hydride shift.

Question 5

In the presence of peroxides (ROOR), the addition of HBr to an alkene proceeds via a free-radical mechanism. What is the major product?

Accepted Answer

The anti-Markovnikov product.

Question 6

Which of the following reagents will NOT result in anti-Markovnikov addition to an alkene?

Accepted Answer

$$\mathrm{HCl}$$ with peroxides

Question 7

Which of the following is true about the hydration of alkenes using dilute sulfuric acid?

Accepted Answer

The reaction proceeds via a carbocation intermediate and follows Markovnikov’s rule.

Question 8

What is the chief product of the acid-catalyzed hydration of 2-methyl-2-butene?

Accepted Answer

$$(\mathrm{CH_3$})_2\mathrm{C(OH)CH_2CH_3}$$

Question 9

Which statement best describes the outcome of oxymercuration-demercuration of an alkene?

Accepted Answer

It gives the Markovnikov alcohol with anti addition and no carbocation rearrangement.

Question 10

Which of the following is a key feature of hydroboration-oxidation of alkenes?

Accepted Answer

The addition of water is anti-Markovnikov and syn.

Question 11

Which of the following best describes the stereochemistry of halogen addition (e.g., Br$$_2) to an $$alkene?

Accepted Answer

Anti addition, forming a trans-dihalide.

Question 12

When an alkene reacts with Br$$_2 in $$water, what is the major product?

Accepted Answer

A halohydrin, with Br and OH on adjacent carbons.

Question 13

Which of the following reagents will convert an alkene to a syn-1,2-diol?

Accepted Answer

$$\mathrm{$$OsO_4$$}$$ followed by $$\mathrm{H_2O_2}$$

Question 14

Which of the following statements about ozonolysis of alkenes is correct?

Accepted Answer

Ozonolysis cleaves the double bond to give aldehydes and/or ketones.

Question 15

Which of the following best explains why only HBr, and not HCl or HI, undergoes free-radical addition to alkenes in the presence of peroxides?

Accepted Answer

The reaction of an alkyl radical with HBr is exothermic, while with HCl or HI it is endothermic.

Question 16

Which of the following is a diagnostic chemical test for the presence of a carbon-carbon double bond?

Accepted Answer

Addition of Br$$_2 in $$CCl$$_4$$, resulting in decolorization.

Question 17

Which of the following statements about catalytic hydrogenation of alkenes is correct?

Accepted Answer

Hydrogen adds to the same face of the double bond (syn addition).

Question 18

Which of the following best describes the product(s) of oxidative cleavage of an alkene with warm, concentrated KMnO$$_4$$?

Accepted Answer

Ketones, carboxylic acids, or CO$$_2$$ may be formed, depending on substitution.

Question 19

Which of the following is true about the stereochemistry of epoxidation of alkenes with peroxyacids?

Accepted Answer

The stereochemistry of the alkene is retained in the epoxide.

Chapter 8: Reactions of Alkenes – Mechanisms, Stereochemistry, and Applications

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