Question 1

Which statement best explains why the addition of HBr to propene yields only 2-bromopropane and not 1-bromopropane?

Accepted Answer

The reaction is regioselective due to carbocation stability; the more stable secondary carbocation leads to 2-bromopropane as the major product.

Question 2

Which of the following best describes Markovnikov's Rule in the addition of HX to an alkene?

Accepted Answer

The hydrogen adds to the carbon with the most hydrogens, forming the more stable carbocation intermediate.

Question 3

Which factor contributes most to the increased stability of tertiary carbocations compared to primary carbocations?

Accepted Answer

Hyperconjugation and inductive electron donation from adjacent alkyl groups.

Question 4

During the acid-catalyzed hydration of ethene to ethanol, what is the role of the acid?

Accepted Answer

It acts as a catalyst, being regenerated at the end of the reaction.

Question 5

Which of the following mechanisms avoids carbocation rearrangements and still yields the Markovnikov product when hydrating an alkene?

Accepted Answer

Hydration by oxymercuration-demercuration.

Question 6

What is the stereochemical outcome of the addition of Br$$_2 to $$cyclohexene?

Accepted Answer

Only the trans isomer is formed due to anti addition via a bromonium ion intermediate.

Question 7

Which of the following best describes the regioselectivity of hydroboration-oxidation of alkenes?

Accepted Answer

It is anti-Markovnikov, with OH adding to the less substituted carbon.

Question 8

Which of the following is true about the stereochemistry of hydrogenation of alkenes using a metal catalyst?

Accepted Answer

Hydrogen atoms add to the same face of the double bond (syn addition), resulting in a stereospecific reaction.

Question 9

A secondary carbocation can rearrange to a more stable tertiary carbocation by which process?

Accepted Answer

1,2-hydride shift

Question 10

Which statement about the addition of HX to a chiral alkene is correct?

Accepted Answer

The presence of an asymmetric center near the reacting center leads to diastereoselectivity, producing unequal amounts of diastereomers.

Question 11

Which of the following is a consequence of the cyclic bromonium ion intermediate in halogenation of alkenes?

Accepted Answer

Anti addition of halogen atoms to the double bond.

Question 12

Which reagent combination will convert an alkene to an alcohol with anti-Markovnikov regioselectivity and syn stereochemistry?

Accepted Answer

BH$$_3/$$THF followed by H$$_2O$_2$$, OH$$^-$$

Question 13

Which of the following is NOT a reason for the increased stability of more substituted carbocations?

Accepted Answer

Steric hindrance from bulky groups.

Question 14

In the industrial hydration of ethene to ethanol, which intermediate is formed after the initial electrophilic addition?

Accepted Answer

A carbocation intermediate

Question 15

Which of the following reactions is stereospecific, meaning each stereoisomeric reactant forms a different stereoisomeric product?

Accepted Answer

Bromine addition (Br$$_2) to $$cis-2-butene

Question 16

Which statement best describes the mechanism of alkene epoxidation with a peroxyacid?

Accepted Answer

It is a concerted, cyclic mechanism resulting in syn addition.

Question 17

Which of the following is true about the biological hydration of fumaric acid to malic acid?

Accepted Answer

Fumarase is substrate specific and only catalyzes hydration of the trans isomer (fumaric acid).

Question 18

Which of the following best explains why carbocation rearrangements do not occur during oxymercuration-demercuration?

Accepted Answer

The reaction proceeds via a cyclic mercurinium ion intermediate, preventing rearrangement.

Question 19

Which of the following is a correct statement about regioselective reactions?

Accepted Answer

They preferentially form one constitutional isomer over another.

Reactions of Alkenes and Stereochemistry of Addition Reactions

Study Guide - Practice Questions