Question 1

Which of the following best describes the role of AlCl$$_3 in $$the Friedel-Crafts alkylation reaction?

Accepted Answer

It serves as a Lewis acid, accepting a lone pair from the halide to generate a carbocation.

Question 2

Which statement correctly distinguishes between heterogeneous and homogeneous catalysis in hydrogenation reactions?

Accepted Answer

Heterogeneous catalysts, such as Pd/C, are insoluble and can be filtered out, while homogeneous catalysts, like Wilkinson's catalyst, are dissolved in the reaction mixture.

Question 3

Lindlar’s catalyst is used in the hydrogenation of alkynes. What is the main advantage of using Lindlar’s catalyst over regular Pd/C?

Accepted Answer

It selectively reduces alkynes to cis-alkenes without further reduction to alkanes.

Question 4

Which of the following is a key mechanistic step in the Heck reaction catalyzed by Pd complexes?

Accepted Answer

Oxidative addition of the aryl or vinyl halide to the Pd center.

Question 5

In the Suzuki-Miyaura reaction, what is the primary role of the base?

Accepted Answer

To remove the boronate group, facilitating transmetalation.

Question 6

Which of the following best describes the concept of 'Umpolung' as applied in organolithium chemistry?

Accepted Answer

Reversing the polarity of a carbon atom from electrophilic ($$\delta^+) to $$nucleophilic ($$\delta^-).$$

Question 7

A student attempts to synthesize a phosphonium ylide for a Wittig reaction using a tertiary alkyl iodide and triphenylphosphine. What is the most likely outcome?

Accepted Answer

No reaction occurs because tertiary alkyl halides are poor substrates for SN2 reactions.

Question 8

Which of the following statements about the selectivity of Wilkinson’s catalyst in hydrogenation reactions is correct?

Accepted Answer

It selectively hydrogenates the less hindered, less stable double bond in a molecule.

Question 9

Which of the following is NOT a feature of the Heck reaction?

Accepted Answer

It uses a Grignard reagent as a coupling partner.

Question 10

In the context of C–C bond formation, what is the main difference between the Suzuki-Miyaura and Wittig reactions?

Accepted Answer

The Suzuki-Miyaura reaction couples an organoboron compound with an aryl halide, while the Wittig reaction couples a phosphonium ylide with a carbonyl compound.

Question 11

Which of the following best explains why a chiral ligand in a Pd-catalyzed reaction can lead to the formation of a new chiral center in the product?

Accepted Answer

The chiral ligand creates an asymmetric environment around the metal center, favoring one enantiomer over the other.

Question 12

Which of the following is a necessary condition for the successful coupling of two alkyl groups using a Gilman reagent (R$$_2$$CuLi)?

Accepted Answer

The alkyl halide must be primary.

Question 13

A chemist wants to synthesize an alkene from a ketone using a Wittig reaction. Which of the following reagents is essential for this transformation?

Accepted Answer

A phosphonium ylide

Question 14

Which of the following steps is common to both the Heck and Suzuki-Miyaura reactions?

Accepted Answer

Oxidative addition of an aryl halide to a Pd(0) complex

Question 15

In the context of transition metal catalysis, what is meant by 'reductive elimination'?

Accepted Answer

The process by which two ligands on a metal center combine and are released as a new molecule, reducing the oxidation state of the metal.

Question 16

Which of the following statements about the formation of organolithium compounds from alkyl halides is correct?

Accepted Answer

The carbon attached to the halide is reduced from $$+1 to$$ $$-1.$$

Question 17

Which of the following is a reason why triphenylphosphine reacts with primary or secondary alkyl halides but not tertiary alkyl halides in the formation of phosphonium salts?

Accepted Answer

Tertiary alkyl halides are too sterically hindered for an SN2 reaction.

Question 18

Which of the following best describes the product of a Wittig reaction between benzaldehyde and methyltriphenylphosphonium ylide?

Accepted Answer

Styrene

Question 19

A chemist performs a Suzuki-Miyaura coupling between phenylboronic acid and 4-bromotoluene. What is the expected product?

Accepted Answer

4-Methylbiphenyl

Question 20

Which of the following is a key difference between the use of Grignard reagents and organolithium reagents in organic synthesis?

Accepted Answer

Organolithium reagents are generally more reactive and can be used to prepare Gilman reagents for coupling reactions.

Catalysis in Organic Chemistry: Lewis Acids, Transition Metals, and C–C Bond Formation

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