Deck 22: The Chemistry of Enolate Ions, Enols, and Α,β-Unsaturated Carbonyl Compounds

Question 1

Give both enolates formed from deprotonation of the given ketone with base and draw a curved-arrow mechanism to show how they are formed.

Answer 1

The enolate is formed by deprotonation of an alpha carbon. There is only one alpha proton that can be deprotonated since the other alpha proton is vinyl. Deprotonation forms a carbanion whose electrons can be delocalized to the oxygen to form the other enolate.

Question 2

Write an arrow-pushing mechanism for the isomerization of enol to cyclohexanone under (a) aqueous acidic conditions and (b) aqueous basic conditions. Show all proton transfer steps in each mechanism and two resonance structures for each intermediate.

Answer 2

(a) The acidic mechanism starts with protonation of the alkene to form a carbocation, which can be stabilized by the nearby hydroxy group.
(b) The basic mechanism starts by deprotonating the alcohol.

Question 3

Choose the reaction conditions that would convert acetophenone to methyl benzoate in the best yield.

A) step 1: NaBH₄ in methanol; step 2: heat the product of step 1 in aqueous H₂SO₄
B) step 1: Br₂ in acetic acid; step 2: heat the product of step 1 in methanol
C) step 1: excess Br₂ in aqueous NaOH; step 2: heat the product of step 1 with methanol in aqueous NaOH
D) step 1: excess Br₂ in aqueous NaOH; step 2: treat the product of step 1 with methanol in catalytic H₂SO₄

Answer 3

D

Question 4

When allowed to react with D₂O in the presence of a trace amount of NaOD, which hydrogens in the molecule will be exchanged by deuterium (D)?

A) H_a
B) H_b
C) H_c
D) H_a and H_b
E) H_a and H_c

Question 5

Predict the major organic product for the reaction. If you believe no reaction would occur, write NR.

Question 6

Indicate the missing starting material and product, given the conditions provided. When filling in the product, indicate only the major organic product(s). If you believe no reaction would occur, write NR.

Question 7

Deduce the structure of the starting material given the product and conditions.

Question 8

Deduce the structure of the starting material given the product and conditions.

Question 9

Choose the best reagent(s) for carrying out the conversion.

A) PhMgBr, ether; then aqueous acid
B) PhCH₂MgBr, ether; then aqueous acid
C) Ph₃P=CHPh
D) LiCuPh₂, ether

Question 10

One equivalent of ethanethiol reacts with a naphthalene-1,4-dione derivative to yield primarily A or B, but not both.
​a. Show a reaction mechanism for the formation of the favored product, and state in 10 words or less why your choice is favored over the other.
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b. The actual observed product of this reaction is different than either A or B. The observed product shows no C=O stretch in IR. Show this product below, and in 10 words or less, state why this actual product forms.

Question 11

Predict the major organic product for the reaction. If you believe no reaction would occur, write NR.

Question 12

Which of these compounds could not have been prepared by an aldol addition/condensation reaction?

A) compound A
B) compound B
C) compound C
D) compound D
E) compounds B and C

Question 13

Predict the major organic product for the reaction. If you believe no reaction would occur, write NR.

Question 14

The deuterium exchange of the compound replaces all the protons. The hydrogen labeled with an asterisk is not normally acidic, as it cannot be resonance stabilized. Explain how this hydrogen is able to undergo a deuterium exchange.

Question 15

Name the condensation reaction that forms this molecule and identify the starting material that would be needed.

Question 16

Can this compound be prepared in good yield by an aldol reaction? If so, give the starting materials. If not, explain why.

Question 17

Can this compound be prepared in good yield by an aldol reaction? If so, give the starting materials. If not, explain why.

Question 18

Which is true of the Claisen condensation?

A) The product is an $\alpha$ -ketoester.
B) The enolate formed undergoes a nucleophilic acyl substitution reaction with a second molecule of ester.
C) The condensation can occur under both acidic and basic conditions.
D) The starting materials are an ester enolate and an aldehyde or ketone.

Question 19

Which ester cannot be used in a Claisen condensation?

A) compound A
B) compound B
C) compound C
D) compound D

Question 20

Outline a malonic ester synthesis of the carboxylic acid.

Question 21

Only one of these three carboxylic acids can be synthesized from the malonic ester synthesis. Circle the compound that can be synthesized and explain why the other two carboxylic acids cannot be synthesized using the malonic ester synthesis.

Question 22

This compound can be formed from a condensation reaction. Name the reaction and draw the precursor to the condensation reaction.

Question 23

The reaction of lithium aluminum hydride with the $\alpha$ , $\beta$ -unsaturated ketone forms either compound A or

Question 24

Outline a synthesis for the transformation of acetone to a tertiary alcohol. The phenyl group should come from PhLi.

Question 25

Outline a one-step synthesis for the transformation. Hint: Use an organometallic reagent.