Q: Which of the following compounds would have the most acidic $$ ext{α}-$$hydrogen?

$$\text{CH}_3\text{COCH}_2\text{COCH}_3 (2$$,4-pentanedione)

Q: Which product is formed in the aldol reaction between two molecules of acetaldehyde under basic conditions?

$$\text{CH}_3\text{CH}(OH)\text{CH}_2\text{CHO} (a$$ $$\beta-$$hydroxyaldehyde)

Question 1

Which of the following best explains why the $$	ext{p}K_a of $$the $$	ext{α}-$$hydrogen in 2,4-pentanedione is significantly lower than that of acetone?

Accepted Answer

The presence of two carbonyl groups allows for greater resonance stabilization of the conjugate base.

Question 2

In the base-catalyzed keto-enol tautomerism, what is the first mechanistic step?

Accepted Answer

Removal of a proton from the $$	ext{α}-$$carbon by hydroxide ion

Question 3

Which statement best describes the equilibrium between keto and enol tautomers for simple ketones such as acetone?

Accepted Answer

The keto form is strongly favored due to the strength of the C=O bond.

Question 4

Which of the following compounds would have the most acidic $$	ext{α}-$$hydrogen?

Accepted Answer

$$	ext{CH}_3	ext{COCH}_2	ext{COCH}_3 (2$$,4-pentanedione)

Question 5

During the acid-catalyzed keto-enol tautomerism, which atom is protonated first?

Accepted Answer

The carbonyl oxygen

Question 6

Which product is formed in the aldol reaction between two molecules of acetaldehyde under basic conditions?

Accepted Answer

$$	ext{CH}_3	ext{CH}(OH)	ext{CH}_2	ext{CHO} (a$$ $$\beta-$$hydroxyaldehyde)

Question 7

Which of the following best describes the role of aldolase in the biosynthesis of fructose-1,6-bisphosphate?

Accepted Answer

It catalyzes a crossed aldol reaction between dihydroxyacetone phosphate and glyceraldehyde-3-phosphate.

Question 8

Why are $$	ext{α}-$$hydrogens of esters less acidic than those of ketones?

Accepted Answer

The resonance stabilization of the conjugate base is less effective due to the electron-donating alkoxy group.

Question 9

Which of the following is a necessary condition for a molecule to undergo an aldol reaction?

Accepted Answer

It must have at least one enolizable $$	ext{α}-$$hydrogen.

Question 10

In the mechanism of the base-catalyzed aldol reaction, what is the nucleophile that attacks the carbonyl carbon?

Accepted Answer

The enolate ion

Question 11

Which of the following best explains why the enol form of phenol is more stable than the keto form?

Accepted Answer

The enol form is stabilized by aromaticity.

Question 12

Which of the following statements about keto-enol tautomerism is correct?

Accepted Answer

Keto and enol tautomers are constitutional isomers.

Question 13

Which step in the acid-catalyzed tautomerism mechanism directly leads to the formation of the enol tautomer?

Accepted Answer

Removal of a proton from the $$	ext{α}-$$carbon

Question 14

Which of the following best describes the new bond formed in an aldol reaction?

Accepted Answer

A bond between the $$	ext{α}-$$carbon of one molecule and the carbonyl carbon of another

Question 15

Which of the following is a real-life application of the aldol reaction?

Accepted Answer

Biosynthesis of fructose-1,6-bisphosphate in glycolysis

Question 16

Which of the following best explains why the enol content is higher in compounds where the enol form is stabilized by hydrogen bonding or conjugation?

Accepted Answer

Stabilization of the enol form lowers its energy, shifting the equilibrium toward the enol.

Reactions at the α-Carbon of Carbonyl Compounds

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