Question 1

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

Accepted Answer

The alpha hydrogen is adjacent to an electron-withdrawing carbonyl group, which stabilizes the resulting enolate ion through resonance.

Question 2

In the Claisen condensation, why must the two ester molecules have the same alkyl group?

Accepted Answer

To prevent transesterification and ensure that the alkoxy group leaving matches the base used, avoiding side reactions.

Question 3

Which of the following is the correct overall reaction for the synthesis of ethyl acetoacetate via Claisen condensation?

Accepted Answer

$$2\ \mathrm{CH_3COOCH_2CH_3}\ +\ \mathrm{NaOCH_2CH_3}\ \rightarrow\ \mathrm{CH_3COCH_2COOCH_2CH_3}\ +\ \mathrm{C_2H_5OH}\ +\ \mathrm{NaCl}$$

Question 4

Which of the following best describes the Dieckmann condensation?

Accepted Answer

An intramolecular Claisen condensation that forms a cyclic beta-ketoester from a diester.

Question 5

A student attempts a Dieckmann condensation with a seven-membered ring diester. What is the most likely outcome?

Accepted Answer

The reaction will have a low yield due to competition from intermolecular reactions and ring strain.

Question 6

Which of the following is a key difference between the Claisen condensation and the aldol condensation?

Accepted Answer

Claisen condensation involves esters and forms beta-ketoesters, while aldol condensation involves aldehydes or ketones and forms beta-hydroxy carbonyl compounds.

Question 7

Which of the following compounds is considered an 'active methylene' compound due to its enhanced acidity?

Accepted Answer

$$\mathrm{CH_2$(COOC_2H_5)_2} ($$diethyl malonate)

Question 8

In a laboratory crossed aldol condensation between acetone and benzaldehyde, why is benzaldehyde added to the base before acetone?

Accepted Answer

To prevent self-condensation of acetone and ensure selective formation of the desired product.

Question 9

Which of the following best describes the product of an aldol condensation followed by dehydration?

Accepted Answer

An $$\alpha,\beta-$$unsaturated carbonyl compound

Question 10

Which base is commonly used to generate the enolate ion in directed aldol reactions for high selectivity?

Accepted Answer

Lithium diisopropyl amide (LDA)

Question 11

Which of the following statements about the acidity of alpha hydrogens in active methylene compounds is correct?

Accepted Answer

Alpha hydrogens in active methylene compounds have pKa values between 3 and 13, making them much more acidic than typical alkyl hydrogens.

Question 12

Which of the following is a synthetic application of the acetoacetic ester synthesis?

Accepted Answer

Preparation of methyl ketones via alkylation, hydrolysis, and decarboxylation.

Question 13

Which of the following best explains why crossed aldol reactions can produce complex mixtures?

Accepted Answer

Both reactants may have alpha hydrogens, allowing multiple possible enolate and electrophile combinations.

Question 14

Which of the following is a key mechanistic step in the Claisen condensation?

Accepted Answer

Deprotonation of the alpha hydrogen to form an enolate ion, which then attacks the carbonyl carbon of another ester.

Question 15

Which of the following statements about conjugate (1,4-) addition to alpha, beta-unsaturated carbonyl compounds is correct?

Accepted Answer

The nucleophile adds to the beta carbon, resulting in a saturated carbonyl compound.

Question 16

Which of the following is NOT an example of an active hydrogen compound?

Accepted Answer

$$\mathrm{C_6H_6} ($$benzene)

Question 17

A student performs a malonic ester synthesis, alkylating diethyl malonate with an alkyl halide, then hydrolyzing and decarboxylating. What is the final product?

Accepted Answer

A substituted acetic acid

Question 18

Which of the following best describes the resonance stabilization of the enolate ion formed from a carbonyl compound?

Accepted Answer

The negative charge is delocalized between the alpha carbon and the oxygen atom.

Question 19

Which of the following is a practical strategy to obtain a single product in a crossed aldol condensation?

Accepted Answer

Use one reactant with no alpha hydrogens and add it to the base before the other reactant.

Enolate Chemistry: Claisen, Dieckmann, Malonic Ester, and Aldol Condensations

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