Organic Chemistry 2 Quiz: Aldol Reactions Addition Condensation

What this quiz covers

This quiz focuses on Aldol Reactions Addition Condensation, giving you a quick way to practice the rules, question types, and explanations that matter most for Organic Chemistry 2.

How to use this quiz

Try each quiz question before looking at the correct answer. Use the explanations to review missed ideas, then come back to similar questions until the pattern feels familiar.

Question 1

1. β-hydroxy aldehyde or β-hydroxy ketone (correct answer)
2. α,β-unsaturated carbonyl compound
3. Carboxylic acid via oxidation
4. Ester via nucleophilic acyl substitution

Question 2

1. Resonance stabilization of the conjugate base (enolate) (correct answer)
2. Hyperconjugation that destabilizes the conjugate base
3. Aromaticity gained by deprotonating the carbonyl oxygen
4. Leaving-group ability of the α-hydrogen as H$^-$

Question 3

1. The electrophile is typically the carbonyl carbon of an aldehyde or ketone (correct answer)
2. The electrophile is always the enolate oxygen due to negative charge
3. The electrophile is hydroxide, which accepts electron density
4. The electrophile is the α-carbon because it bears acidic hydrogens

Question 4

1. An α,β-unsaturated aldehyde (enal) formed directly
2. A β-hydroxy aldehyde (the aldol) after protonation of the alkoxide (correct answer)
3. A β-keto aldehyde formed by acyl substitution
4. A diol formed by double hydroxide addition

Question 5

1. The product formed from the attack of the more substituted (thermodynamic) enolate on acetaldehyde.
2. The product formed from the attack of the less substituted (kinetic) enolate on acetaldehyde. (correct answer)
3. A product resulting from the self-condensation of 2-methylcyclohexanone.
4. A product where the enolate of acetaldehyde attacks the 2-methylcyclohexanone carbonyl.

Question 6

1. The mono-aldol condensation product, 2-benzylidenecyclopentanone.
2. The di-aldol condensation product, 2,5-dibenzylidenecyclopentanone. (correct answer)
3. The Cannizzaro products of benzaldehyde: benzyl alcohol and sodium benzoate.
4. The self-condensation product of cyclopentanone.

Question 7

1. At 80 °C, the retro-aldol reaction would dominate, yielding no product; at 5 °C, the addition product would form.
2. There would be no significant difference in the product distribution, as temperature only affects the reaction rate.
3. At 80 °C, the thermodynamic enolate would form, while at 5 °C the kinetic enolate would form, leading to different isomers.
4. At 80 °C, the α,β-unsaturated condensation product would dominate; at 5 °C, the β-hydroxy ketone addition product would dominate. (correct answer)

Question 8

1. Running the reaction at very low temperature (-78 °C) to trap the addition intermediate.
2. Using a full equivalent of a strong base like LDA instead of a catalytic amount of NaOH.
3. Adding a strong dehydrating agent like P₂O₅ to the reaction mixture.
4. Arranging the apparatus for distillation to remove water as it is formed (e.g., using a Dean-Stark trap). (correct answer)

Question 9

1. Treatment with a strong acid and a dehydrating agent.
2. Storage at low temperature (0 °C) in a neutral aqueous solution.
3. Treatment with a strong base (e.g., NaOH) at an elevated temperature. (correct answer)
4. Reaction with NaBH₄ in ethanol.

Question 10

1. A carbocation located at the β-carbon.
2. The enol tautomer of the β-hydroxy ketone.
3. An enolate ion with the negative charge on the α-carbon. (correct answer)
4. A tetrahedral alkoxide formed by the attack of a hydroxide ion on the carbonyl.

Question 11

1. 3-Pentanone cannot act as an effective electrophile in aldol reactions due to steric hindrance.
2. The reaction is reversible, and the equilibrium strongly favors the starting materials under these conditions.
3. Both ketones can act as both the enolate nucleophile and the carbonyl electrophile, leading to four potential products. (correct answer)
4. The desired product is unstable and rapidly decomposes in the basic reaction medium.

Question 12

1. A cyclic β-hydroxy ketone that cannot dehydrate
2. A cyclic α,β-unsaturated carbonyl formed after aldol addition and dehydration (correct answer)
3. A cyclic acetal formed by intramolecular alcohol addition
4. A cyclic ether formed by Williamson ether synthesis

Question 13

1. A β-hydroxy carbonyl compound (correct answer)
2. A geminal diol (hydrate) of the carbonyl
3. An epoxide formed from intramolecular SN2
4. An acyl chloride formed in situ

Question 14

1. LDA in THF at $-78\,^{\circ}\mathrm{C}$
2. LiHMDS in THF at low temperature
3. NaOH in water at reflux (correct answer)
4. KHMDS in THF at low temperature

Question 15

1. C=O becomes C–O and C–C becomes C=C with O–H formation (correct answer)
2. C–C becomes C≡C with loss of H$_2$
3. C=O becomes C–OH and C–C remains single throughout
4. C=O becomes C–NH and C–C becomes C=N

Question 16

1. The ipso aromatic carbon attached to CHO
2. The benzaldehyde carbonyl carbon (correct answer)
3. The benzaldehyde carbonyl oxygen
4. The benzylic carbon adjacent to the aromatic ring

Question 17

1. LDA, THF, low temperature (e.g., $-78\,^{\circ}\mathrm{C}$), short time (correct answer)
2. NaOEt, EtOH, room temperature, long time
3. H$_3$O$^+$, heat, long time
4. NaOH, H$_2$O, reflux, long time

Question 18

1. Enolates are protonated enols and are less nucleophilic
2. Enols are resonance forms of enolates with identical charge distribution
3. Enolates are deprotonated enols (or α-deprotonated carbonyls) and are stronger nucleophiles (correct answer)
4. Enols form only under strongly basic conditions, not acidic conditions

Question 19

1. Benzaldehyde has no α-hydrogens, so it cannot form an enolate nucleophile (correct answer)
2. Benzaldehyde is a base, so it suppresses acetone enolate formation
3. Benzaldehyde is less electrophilic than acetone, so it never reacts
4. Benzaldehyde undergoes rapid acyl substitution, consuming hydroxide

Question 20

1. Base removes the β-OH proton, then OH$^-$ leaves to form a carbocation
2. Base removes an α-proton to form an enolate, then elimination expels OH$^-$ (correct answer)
3. Water attacks the carbonyl carbon, then hydride leaves
4. Alkoxide attacks the β-carbon, then O$^{2-}$ leaves