Question 1

Which of the following statements best explains why the alpha-hydrogen of a ketone is more acidic than the hydrogen of an alkane?

Accepted Answer

The electrons left behind after deprotonation are delocalized onto an oxygen atom, stabilizing the conjugate base.

Question 2

Given the following compounds, which has the lowest $$pK_a$$ for its alpha-hydrogen and why?

1. $$\mathrm{CH_3CH_2NO_2}
2$$. $$\mathrm{CH_3CH_2C \equiv N}
3$$. $$\mathrm{CH_3CON(CH_3$)_2}$$

Accepted Answer

$$\mathrm{CH_3CH_2NO_2}$$, because the negative charge can be delocalized onto two oxygens, greatly stabilizing the conjugate base.

Question 3

Which product is formed when 2-methylcyclohexanone is treated with LDA followed by methyl iodide at $$-78^\circC$$?

Accepted Answer

2,6-dimethylcyclohexanone

Question 4

Which of the following best describes the difference between kinetic and thermodynamic enolate formation?

Accepted Answer

The kinetic enolate forms faster and is less substituted, while the thermodynamic enolate is more stable and more substituted.

Question 5

In the Hell–Volhard–Zelinski (HVZ) reaction, what is the role of $$\mathrm{$$PBr_3$$}$$?

Accepted Answer

It converts the carboxylic acid to an acyl bromide, activating the alpha-hydrogen for bromination.

Question 6

Which of the following statements about aldol addition reactions is correct?

Accepted Answer

The product contains a new C–C bond between the alpha-carbon of one molecule and the carbonyl carbon of another.

Question 7

Why does the enol tautomer of phenol predominate over the keto tautomer?

Accepted Answer

The enol tautomer is aromatic, which provides extra stabilization.

Question 8

Which of the following is a key difference between acid-catalyzed and base-promoted halogenation of ketones?

Accepted Answer

Acid-catalyzed halogenation replaces only one alpha-hydrogen, while base-promoted halogenation replaces all alpha-hydrogens.

Question 9

Which of the following best explains why the product of a Claisen condensation must have at least two alpha-hydrogens?

Accepted Answer

A second alpha-hydrogen is removed to drive the reaction to completion and prevent reversal.

Question 10

Which of the following statements about the Michael reaction is correct?

Accepted Answer

It is a conjugate addition of an enolate ion to an alpha, beta-unsaturated carbonyl compound, forming a 1,5-dicarbonyl product.

Question 11

In a crossed aldol condensation between benzaldehyde (no alpha-hydrogens) and acetone (with alpha-hydrogens), which strategy will maximize the yield of a single product?

Accepted Answer

Add benzaldehyde slowly to a solution of acetone and base.

Question 12

Which of the following is a correct retrosynthetic disconnection for the synthesis of a beta-hydroxyketone via aldol addition?

Accepted Answer

Disconnect the bond between the alpha-carbon of one ketone and the carbonyl carbon of another.

Question 13

Which of the following is true about the acetoacetic ester synthesis?

Accepted Answer

It forms a methyl ketone with three more carbons than the alkyl halide used.

Question 14

Which of the following is a reason why enamines are used instead of enolate ions for alkylation reactions?

Accepted Answer

Enamines react with electrophiles under milder conditions, avoiding the need for strong bases.

Question 15

Which of the following best describes the product of a Dieckmann condensation?

Accepted Answer

A cyclic beta-keto ester formed by intramolecular Claisen condensation.

Question 16

Which of the following is a requirement for a successful Claisen-Schmidt condensation?

Accepted Answer

One reactant must lack alpha-hydrogens, typically an aromatic aldehyde.

Question 17

Which of the following statements about the E1cb mechanism in aldol condensation is correct?

Accepted Answer

It involves the formation of a stabilized carbanion intermediate before elimination.

Question 18

Which of the following is a key step in the malonic ester synthesis?

Accepted Answer

Alkylation of the alpha-carbon followed by decarboxylation to yield a substituted acetic acid.

Reactions at the Alpha-Carbon: Mechanisms, Reactivity, and Synthetic Applications

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