Deck 23: Substitution Reactions of Carbonyl Compounds at the Alpha-Carbon

Question 1

Which of the following is the intermediate for halogenation of ketones under acidic conditions?

A)An enolate
B)An enol
C)A tautomer
D)An epimer

Answer 1

An enol

Question 2

What is the product of the following reaction?

A)I
B)II
C)III
D)IV

Answer 2

IV

Question 3

What is the starting material in the following reaction?

A)I
B)II
C)III
D)IV

Answer 3

IV

Question 4

What is the starting material for the following reaction?

A)I
B)II
C)III
D)IV

Question 5

Why is the enolate of acetone less basic than the allyl anion derived from propene?

A)Because there are more atoms in acetone
B)Because there are more resonance structures for the enolate of acetone
C)It isn't; the allyl anion is less basic.
D)One of the resonance structures for the enolate places the negative charge on the more electronegative oxygen.

Question 6

What are the three steps in the malonic ester synthesis?

A)Deprotonation, alkylation, hydrolysis/decarboxylation
B)Hydrogenation, alkylation, deprotonation
C)Alkylation, hydrolysis/decarboxylation.hydrogenation
D)Hydrolysis/decarboxylation, deprotonation, alkylation

Question 7

Why is it difficult to stop the halogenation of ketones under basic conditions at the mono-halogenated stage?

A)The ketone undergoes a Bayer-Villigar oxidation.
B)The ketone is reduced.
C)The ketone undergoes an Aldol reaction.
D)The bromine helps to stabilize the second enolate, making the product more acidic than the starting material.

Question 8

Starting with cyclohexanone, how could you prepare the diketone below?

A)Treat cyclohexanone with a base under thermodynamic conditions.
B)Hydrogenate cyclohexanone with Raney nickel.
C)Convert cyclohexanone into the a-bromoketone and then react this with the enolate of cyclohexanone.
D)Convert cyclohexanone into an enamine with diethylamine and then react this with more cyclohexanone.

Question 9

What is the missing reagent for the following reaction?

A)Br₂/HOAc
B)Br₂/KOH
C)Cl₂/FeCl₃
D)Br₂/FeBr₃

Question 10

Which of the following is an enol form of the following compound?

A)I
B)II
C)III
D)IV

Question 11

Which is the kinetic enolate of 2-methylcyclohexanone?

A)I
B)II
C)III
D)IV

Question 12

Which of the following four compounds is the most acidic?

A)I
B)II
C)III
D)IV

Question 13

Will acetophenone be completely deprotonated by lithium diisopropylamide (LDA)?

A)Yes
B)No

Question 14

Which is the more stable form of acetophenone?

A)Only I
B)Only II
C)Only III
D)I and II are equally stable

Question 15

What is the product of the following reaction?

A)I
B)II
C)III
D)IV

Question 16

If you want to form a thermodynamic enolate, you want to:

A)Keep the reaction as cold as possible.
B)Use an aprotic solvent such as THF.
C)Use a protic solvent such as ethanol.
D)Use a carboxylic acid.

Question 17

What is (are) the product(s) of the following reaction?

A)Only I
B)Only II
C)Only III
D)Only I and III

Question 18

What is the missing reagent in the reaction below?

A)Br₂/AcOH
B)I₂/KOH
C)I₂
D)KOH

Question 19

If you want to form a kinetic enolate, you want to:

A)Use a strong, non-nucleophilic base such as LDA.
B)Use a protic solvent.
C)Use a low temperature.
D)Both use a strong, non-nucleophilic base such as LDA and use a low temperature.

Question 20

Will acetone be completely deprotonated by potassium tert-butoxide?

A)Yes
B)No

Question 21

Which of the following compounds would undergo racemization in the presence of a base?

A)I
B)II
C)III
D)IV

Question 22

What is the starting material required to accomplish the following transformation?

A)I
B)II
C)III
D)IV

Question 23

Which of the following compounds is an enol of compound X drawn below?

A)Only I
B)Only II
C)Only III
D)Only I and II

Question 24

Vitamin C is a stable enediol.Which is the structure of a possible keto form in equilibrium with the enediol form?

A)I
B)II
C)III
D)IV

Question 25

What is the structure of X, product of the following reaction?

A)I
B)II
C)III
D)IV

Question 26

Which is the most acidic proton in the following compound?

A)I
B)II
C)III
D)IV

Question 27

Which of the following bases will completely convert 1,4-cyclohexandione into an enolate?

A)Sodium hydroxide
B)Sodium methoxide
C)Sodium tert-butoxide
D)Sodium hydride

Question 28

Which is the thermodynamic enolate of 2-methylcyclohexanone?

A)I
B)II
C)III
D)IV

Question 29

Which is the most acidic proton in the following compound?

A)I
B)II
C)III
D)IV

Question 30

Which of the following ketones will give a positive iodoform test?

A)3-Heptanone
B)2-Pentanone
C)3-Hexanone
D)Cyclohexanone

Question 31

Which of the following are enol forms of ethyl acetoacetate drawn below?

A)Only I
B)Only II
C)Only III
D)I, II, and III

Question 32

For most compounds with a single keto group in the molecule, equilibrium favors the keto form over the enol form of the compound.This is due largely to what?

A)The C=O bond is much stronger than the C=C bond.
B)The C=C bond is much stronger than the C=O bond.
C)The keto form can undergo intramolecular hydrogen bonding.
D)The enol form can undergo intramolecular hydrogen bonding.

Question 33

Select the appropriate sequence of reactions to accomplish the following synthesis.

A)[1] Br₂, CH₃CO₂H; [2] Li₂CO₃, LiBr, DMF; [3] CH₃CH₂CH₂CH₂Br
B)[1] Br₂, CH₃CO₂H; [2] Mg, Et₂O; [3] CH₃CH₂CH₂CH₂Br
C)[1] LDA; [2] BrCH₂CH₂CH₂CH₂Br; [3] NaOEt
D)[1] NaOEt; [2] BrCH₂CH₂CH₂CH₂Br; [3] LDA

Question 34

What is the major product of the following reaction?

A)I
B)II
C)III
D)IV

Question 35

The following molecule is called:

A)a 1,3-diketopentanoate.
B)a diethyl malonate.
C)an ethyl acetoacetate.
D)a b-keto ester.

Question 36

Which of the following compounds is the most acidic?

A)Ethyl acetoacetate
B)2-Butanone
C)1-Butanol
D)3-Pentanone

Question 37

A simple chemical test to distinguish between acetone and 3-pentanone would be the reaction of the compounds with

A)bromine with acetic acid.
B)bromine and aqueous hydroxide ion.
C)THF, LDA at -78 °C followed by reaction with bromine.
D)base and methyl bromide.

Question 38

The malonic ester synthesis can be adapted to synthesize a-amino acids by using diethyl acetamidomalonate as the starting material.Select the structure of the amino acid produced by the following synthesis.

A)I
B)II
C)III
D)IV

Question 39

The reaction below is a direct enolate alkylation.It has been found that this reaction only works well with unhindered methyl and 1° alkyl halides.Pick the statement that best explains this observation.

A)The nucleophilic enolate requires a reaction center that has a positive charge.
B)Hindered alkyl halides do not undergo S_N1 reactions.
C)Hindered alkyl halides do not undergo S_N2 reactions.
D)Methyl and 1° alkyl halides can form carbocations that can readily react with the nucleophilic enolate.

Question 40

It has been found that b-dicarbonyl compounds have a greater concentration of the enol form over the keto form.This can be explained by:

A)The C=C of the enol is conjugated with the carbonyl group.
B)The -OH of the enol can hydrogen bond to the oxygen of the nearby carbonyl group.
C)Both A and B above are true.
D)None of the choices are true.