Q: A chemist wants to convert cyclohexene to trans-1,2-cyclohexanediol. Which reagent should be used?

$$\mathrm{m\text{-}CPBA}$$ followed by aqueous acid

Question 1

Which reagent is commonly used for the epoxidation of alkenes via peroxyacid oxidation, and what is the major product when cyclohexene reacts with this reagent?

Accepted Answer

meta-chloroperoxybenzoic acid (m-CPBA); cyclohexene oxide

Question 2

During acid-catalyzed ring opening of epoxides, which carbon does the nucleophile preferentially attack and why?

Accepted Answer

The more substituted carbon, because it carries a greater partial positive charge after protonation of the epoxide oxygen.

Question 3

What is the product of the following reaction: $$\mathrm{CH_2$=CH_2$}$$ treated with $$\mathrm{m	ext{-}CPBA} in$$ $$\mathrm{CH_2Cl_2}$$?

Accepted Answer

Ethylene oxide

Question 4

In base-catalyzed ring opening of epoxides, which carbon does the nucleophile attack and what is the mechanistic reason?

Accepted Answer

The less substituted carbon, because the reaction proceeds via an $$\mathrm{S_N2}$$ mechanism.

Question 5

Which of the following best describes the stereochemistry of dihydroxylation of alkenes using $$\mathrm{$$OsO_4$$}$$?

Accepted Answer

Syn addition, resulting in cis-1,2-diols

Question 6

A student treats 1-methylcyclohexene with $$\mathrm{Br_2$}$$ and water. What is the major product and its stereochemistry?

Accepted Answer

Trans-1-bromo-2-hydroxy-1-methylcyclohexane (anti addition)

Question 7

Which of the following statements is true regarding the oxidative cleavage of alkenes using $$\mathrm{O_3$}$$ followed by reductive workup ($$\mathrm{Zn/H_2O}$$)?

Accepted Answer

The double bond is cleaved to form aldehydes and/or ketones, depending on substitution.

Question 8

What is the expected product when 1,2-epoxycyclohexane is treated with ethanol under acidic conditions?

Accepted Answer

Trans-2-ethoxycyclohexanol (nucleophile attacks more substituted carbon)

Question 9

Which of the following is a correct statement about the mechanism of halohydrin formation from alkenes?

Accepted Answer

The reaction proceeds via anti addition of halogen and water across the double bond.

Question 10

A chemist wants to convert cyclohexene to trans-1,2-cyclohexanediol. Which reagent should be used?

Accepted Answer

$$\mathrm{m	ext{-}CPBA}$$ followed by aqueous acid

Question 11

During the base-catalyzed ring opening of an epoxide with $$\mathrm{EtO^-}$$, what is the major product when starting from 1,2-epoxycyclohexane?

Accepted Answer

Trans-2-ethoxycyclohexanol (nucleophile attacks less substituted carbon)

Question 12

Which of the following best explains why nucleophiles attack the less substituted carbon in base-catalyzed epoxide ring opening?

Accepted Answer

Steric hindrance at the more substituted carbon makes the $$\mathrm{S_N2}$$ attack unfavorable.

Question 13

What is the major organic product when 1,2-epoxycyclohexane is treated with $$\mathrm{$$LiAlH_4$$}$$ followed by water?

Accepted Answer

Trans-2-hydroxycyclohexane (hydride attacks less substituted carbon)

Question 14

Which of the following is true about the products of oxidative cleavage of alkynes using $$\mathrm{O_3$}$$?

Accepted Answer

The triple bond is cleaved to produce carboxylic acids and/or ketones.

Question 15

A patient is prescribed a calcium channel blocker that is synthesized via dihydroxylation of an alkene. Which reagent is most likely used in the synthesis?

Accepted Answer

$$\mathrm{$$OsO_4$$}$$

Question 16

Which of the following reactions will result in anti addition across an alkene?

Accepted Answer

Halohydrin formation with $$\mathrm{Br_2$}$$ and water

Question 17

What is the expected product when 1,2-epoxycyclohexane is treated with $$\mathrm{HCl} in $$water?

Accepted Answer

Trans-2-chlorocyclohexanol (nucleophile attacks more substituted carbon)

Question 18

Which of the following best describes the role of protonation in acid-catalyzed epoxide ring opening?

Accepted Answer

Protonation increases the electrophilicity of the epoxide, making the more substituted carbon more susceptible to nucleophilic attack.

Oxidation of Alkenes, Epoxide Ring Opening, and Dihydroxylation of π-Systems

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