Question 1

Which of the following statements best explains why tertiary carbocations are more stable than primary carbocations?

Accepted Answer

Tertiary carbocations have more alkyl groups that donate electron density through hyperconjugation, stabilizing the positive charge.

Question 2

In the electrophilic addition of HBr to 2-methylpropene, which product is formed and why?

Accepted Answer

tert-butyl bromide, because the more stable tertiary carbocation intermediate is formed.

Question 3

Which of the following best describes a regioselective reaction?

Accepted Answer

A reaction in which more of one constitutional isomer is formed than another.

Question 4

What is the major product when 3-methyl-1-butene reacts with HBr, and why?

Accepted Answer

2-bromo-2-methylbutane, due to a 1,2-hydride shift forming a more stable tertiary carbocation.

Question 5

Which of the following is true about the addition of HCl to 1-butene in the presence of $$\mathrm{H_2SO_4}$$?

Accepted Answer

The major product is 2-chlorobutane, because the electrophile adds to the sp$$^2$$ carbon bonded to the most hydrogens.

Question 6

Which of the following best explains why the addition of HBr to 1-butene forms a racemic mixture?

Accepted Answer

The intermediate carbocation is planar, allowing Br$$^- to $$attack from either side, forming two enantiomers.

Question 7

Which of the following is the correct IUPAC name for the compound with the structure $$\mathrm{CH_3CH_2C \equiv CCH_2CH_3}$$?

Accepted Answer

2-hexyne

Question 8

What is the product of the acid-catalyzed addition of water to 1-butyne ($$\mathrm{CH_3CH_2C \equiv CH}) $$followed by tautomerization?

Accepted Answer

$$\mathrm{CH_3CH_2COCH_3} (2-$$butanone)

Question 9

Which catalyst is used to selectively hydrogenate an alkyne to a cis-alkene?

Accepted Answer

Lindlar catalyst

Question 10

Which of the following statements about the addition of Br$$_2 to $$cyclohexene is correct?

Accepted Answer

The reaction proceeds via anti addition, forming only trans-1,2-dibromocyclohexane.

Question 11

Which of the following best describes the difference between regioselective and stereoselective reactions?

Accepted Answer

Regioselective reactions favor one constitutional isomer, while stereoselective reactions favor one stereoisomer.

Question 12

Which of the following is true about the acid-catalyzed hydration of a terminal alkyne?

Accepted Answer

A ketone is formed after tautomerization of the initial enol product.

Question 13

Which of the following is a consequence of carbocation rearrangement during electrophilic addition to alkenes?

Accepted Answer

A more stable carbocation intermediate can form, leading to unexpected major products.

Question 14

Which of the following best explains why the addition of HBr to 2-pentene is not regioselective?

Accepted Answer

Both possible carbocation intermediates are secondary and have similar stability.

Question 15

Which of the following is true about the addition of H$$_2 to a $$cis-alkene using Pd/C?

Accepted Answer

Only the meso compound is formed if the substituents are the same.

Question 16

Which of the following best describes the role of an enzyme in a stereoselective addition reaction?

Accepted Answer

The enzyme forms only one stereoisomer by blocking one face of the reactant.

Question 17

Which of the following is the correct product for the reaction of 2-pentyne with excess HCl?

Accepted Answer

A mixture of 2,2-dichloropentane and 3,3-dichloropentane

Question 18

Which of the following statements about the structure of alkynes is correct?

Accepted Answer

The triple bond consists of one sigma bond and two pi bonds.

Chapter 6: The Reactions of Alkenes and Alkynes – The Stereochemistry of Addition Reactions

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