Question 1

Which of the following statements best explains why addition reactions of alkenes are generally favored at lower temperatures?

Accepted Answer

At lower temperatures, enthalpy dominates, and the formation of stronger sigma bonds from weaker pi bonds is favored.

Question 2

During the hydrohalogenation of 2-methyl-2-butene with HBr (no peroxides), which product is expected to predominate and why?

Accepted Answer

2-bromo-2-methylbutane, due to Markovnikov addition where Br adds to the more substituted carbon.

Question 3

Which of the following best describes the stereochemical outcome when an alkene undergoes bromination (Br$$_2$$ addition) in an inert solvent?

Accepted Answer

Anti addition, resulting in enantiomers if two chiral centers are formed.

Question 4

A student treats 1-methylcyclohexene with aqueous Br$$_2. $$What is the major product and why?

Accepted Answer

A bromohydrin where OH adds to the more substituted carbon and Br to the less substituted carbon, due to the nucleophilic attack of water on the more substituted carbon.

Question 5

Which reagent(s) would you use to convert 1-hexene to 2-hexanol with Markovnikov regioselectivity and without carbocation rearrangement?

Accepted Answer

1. $$\mathrm{Hg(OAc)_2}$$, $$\mathrm{H_2O} 2$$. $$\mathrm{$$NaBH_4$$}$$

Question 6

Which of the following statements about hydroboration-oxidation of alkenes is correct?

Accepted Answer

It proceeds via anti-Markovnikov addition and syn addition of H and OH.

Question 7

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

Accepted Answer

The reaction forms a stabilized mercurinium ion intermediate, which prevents rearrangement.

Question 8

A chemist wants to synthesize 1-bromopropane from propene. Which sequence of reactions would achieve this transformation?

Accepted Answer

Add HBr with peroxides (ROOR) to propene.

Question 9

Which of the following is a key difference between anti dihydroxylation and syn dihydroxylation of alkenes?

Accepted Answer

Anti dihydroxylation proceeds via an epoxide intermediate, while syn dihydroxylation is concerted.

Question 10

Which of the following best describes the product(s) when cis-2-butene is treated with cold, dilute KMnO$$_4$$?

Accepted Answer

A meso-2,3-butanediol, due to syn addition of OH groups.

Question 11

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

Accepted Answer

It requires a metal catalyst and results in syn addition of hydrogen atoms.

Question 12

Which of the following is true regarding the use of chiral catalysts in asymmetric hydrogenation?

Accepted Answer

They allow for the selective formation of one enantiomer over the other.

Question 13

A student wants to convert 2-butanol to 2-butene, then add HBr so that the Br ends up on the terminal carbon. Which sequence of reagents should be used?

Accepted Answer

1. Concentrated $$\mathrm{H_2SO_4} ($$elimination), 2. $$\mathrm{HBr}$$, $$\mathrm{ROOR} ($$anti-Markovnikov addition)

Question 14

Which of the following best explains why halohydrin formation is regioselective for OH addition to the more substituted carbon?

Accepted Answer

The more substituted carbon of the bromonium ion intermediate has more cationic character, making it more susceptible to nucleophilic attack by water.

Question 15

Which of the following sequences would convert 1-butene to 1,2-butanediol with anti stereochemistry?

Accepted Answer

1. $$\mathrm{RCO_3H}$$, 2. $$\mathrm{H_2O}$$, $$\mathrm{H^+}$$

Question 16

Ozonolysis of 1-methylcyclohexene followed by treatment with dimethyl sulfide ($$\mathrm{(CH_3$)_2S}) $$will yield which of the following?

Accepted Answer

A cyclohexanone and an aldehyde (acetone).

Question 17

Which of the following is the correct IUPAC name for the compound with the structure: CH$$_2=$$CHCH$$_2CH$_2CH$_3$$?

Accepted Answer

1-pentene

Question 18

Which of the following statements about the mechanism of acid-catalyzed hydration of alkenes is correct?

Accepted Answer

The reaction proceeds via a carbocation intermediate, which can rearrange if a more stable carbocation is possible.

Question 19

Which of the following best describes the product(s) when trans-2-butene is treated with Br$$_2 in $$CCl$$_4$$?

Accepted Answer

A racemic mixture of enantiomers of 2,3-dibromobutane, due to anti addition.

Addition Reactions of Alkenes: Chapter 8 Study Guide

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