Deck 21: Substitution Reactions of Carbonyl Compounds at the a 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

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

A)Yes
B)No

Answer 3

Yes

Question 4

Which is the kinetic enolate of 2-methylcyclohexanone?

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

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 7

Will acetone be completely deprotonated by potassium tert-butoxide?

A)Yes
B)No

Question 8

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 9

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 10

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

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

Question 11

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 12

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 13

Which is the most stable form of 1,3-cyclohexanedione?

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

Question 14

What is the missing reagent for the following reaction?

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

Question 15

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 16

What is the missing reagent in the reaction below?

A)Br₂/AcOH
B)I₂/KOH
C)I₂
D)KOH

Question 17

Why can't you prepare 2-tert-butylcyclohexanone by the following reaction?

A)Because tert-butyl bromide is too basic.
B)Because tert-butyl bromide cannot undergo an S_N2 reaction.
C)Because tert-butyl bromide is a nucleophile.
D)Because tert-butyl bromide is not a stable compound.

Question 18

What is the product of the following reaction?

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

Question 19

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 20

Which of the following four compounds is the most acidic?

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

Question 21

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 22

What is the starting material in the following reaction?

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

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 25

The following molecule is called

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

Question 26

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 27

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 and above are true.
D)None of the choices are true.

Question 28

Treatment of 2-hexanone with NaOCH₂CH₃ followed by CH₃Br affords compound X (C₇H₁₄O)as the major product.X shows a strong absorption in the IR spectrum at 1713 cm^-1,and its ¹H NMR data is given below.What is the structure of X?

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

Question 29

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 30

What is the starting material for the following reaction?

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

Question 31

Which of the following compounds is the most acidic?

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

Question 32

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

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

Question 33

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 34

Which is the most acidic proton in the following compound?

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

Question 35

What is the major product of the following reaction?

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

Question 36

Which is the most acidic proton in the following compound?

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

Question 37

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 38

Which is the thermodynamic enolate of 2-methylcyclohexanone?

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

Question 39

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

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

Question 40

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 41

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

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

Question 42

Which of the following is the least acidic compound?

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

Question 43

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

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

Question 44

Which of the following would undergo racemization under basic conditions?

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

Question 45

Which of the following is a possible enol form of 2-butanone?

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

Question 46

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 47

Which of the following is the most acidic compound?

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