Question 1

Which statement best explains why the addition of H$$_2 to an $$alkene is thermodynamically favorable?

Accepted Answer

The reaction is exothermic because the $$\pi$$ bond is weaker than the two new C–H bonds formed, resulting in a negative $$\Delta H.$$

Question 2

What is the role of a catalyst such as Pd/C in the hydrogenation of alkenes?

Accepted Answer

It provides a surface for adsorption and lowers the activation energy ($$E_a) $$without being consumed.

Question 3

During catalytic hydrogenation, what is the stereochemical outcome of H$$_2$$ addition to a cycloalkene?

Accepted Answer

Syn addition, resulting in cis products.

Question 4

Which of the following best describes Markovnikov's Rule in the hydrohalogenation of alkenes?

Accepted Answer

The proton (H$$^+) $$adds to the less substituted carbon, forming the more substituted carbocation intermediate.

Question 5

In the halogenation of alkenes (e.g., Br$$_2$$ addition), what is the stereochemical outcome and why?

Accepted Answer

Anti addition due to backside attack on the cyclic bromonium ion intermediate.

Question 6

Which reagent and conditions would convert 4-methyl-1-pentene to 4-methyl-1-pentanol via anti-Markovnikov hydration?

Accepted Answer

1. BH$$_3$$, THF; 2. H$$_2O$_2$$, OH$$^-$$

Question 7

What is the key mechanistic feature of hydroboration-oxidation that leads to its regioselectivity?

Accepted Answer

Steric control: boron adds to the less hindered, less substituted carbon.

Question 8

Which of the following statements about the oxidation of alkenes with peroxycarboxylic acids (e.g., mCPBA) is correct?

Accepted Answer

The reaction forms an epoxide via syn addition.

Question 9

Why does the rate of epoxidation with peroxycarboxylic acids increase with alkyl substitution on the alkene?

Accepted Answer

Alkyl groups stabilize the transition state by donating electron density.

Question 10

Which reagent is used for syn-dihydroxylation of alkenes to form vicinal diols?

Accepted Answer

OsO$$_4$$

Question 11

A student performs the bromine test on an unknown hydrocarbon and observes the solution turns colorless. What does this indicate?

Accepted Answer

The hydrocarbon contains an alkene that reacts with Br$$_2.$$

Question 12

Which of the following best describes the mechanism of halogen addition to alkenes?

Accepted Answer

Formation of a cyclic halonium ion followed by backside attack by halide ion.

Question 13

In the hydroboration of 1-methylcyclopentene, what is the stereochemical relationship between the added H and OH groups in the final product?

Accepted Answer

Cis relationship due to syn addition.

Question 14

Which of the following is NOT a feature of catalytic hydrogenation of alkenes?

Accepted Answer

Forms a carbocation intermediate.

Question 15

What is the product of the reaction between cyclohexene and OsO$$_4$$ followed by H$$_2S$$?

Accepted Answer

cis-1,2-Cyclohexanediol

Question 16

Which of the following reactions is an example of anti-Markovnikov hydration?

Accepted Answer

Hydroboration-oxidation of alkenes

Question 17

What is the main reason that Markovnikov addition occurs in hydrohalogenation reactions?

Accepted Answer

The formation of the more substituted carbocation intermediate is energetically favored.

Question 18

Which of the following is a commonly used peroxycarboxylic acid for epoxidation of alkenes?

Accepted Answer

meta-Chloroperoxybenzoic acid (mCPBA)

Question 19

Which statement best describes the stereochemistry of epoxidation of alkenes with peroxycarboxylic acids?

Accepted Answer

The reaction is stereospecific and proceeds via syn addition.

Reactions of Alkenes: Addition and Oxidation Mechanisms

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