Deck 17: Reactions at the Α-Carbon

Question 1

Which of the following compounds has the most stable enol tautomer?

A)
B)
C)
D)
E)

Answer 1

Question 2

Which of the following is a β-diester?

A)
B)
C)
D)
E)

Answer 2

Question 3

Which of the following underlined alpha hydrogens are the most acidic?

A)
B)
C)
D)
E)

Answer 3

Question 4

Which of the labeled hydrogen atoms in the following structure is the most acidic?

A)1
B)2
C)3
D)4
E)5

Question 5

Draw the most stable enol tautomer of the ketone shown below.

Question 6

Use an asterisk to indicate the most electron-rich carbon in the molecule below.

Question 7

Which compound has the lowest pKa?

A)(CH₃CH₂O₂C)₂CH₂
B)CH₃CH₂O₂CCH₂CHO
C)CH₃CH₂COCH₂CHO
D)PhCOCH₂COCH₃
E)(NC)₂CH₂

Question 8

Which of the labeled hydrogen atoms in the following structure is the most acidic?

A)1
B)2
C)3
D)4
E)5

Question 9

Provide a detailed,stepwise mechanism for the base-catalyzed enolization of acetaldehyde.

Question 10

Which of the following keto-enol tautomers is more stable? Explain.

Question 11

Rank the following compounds in order of increasing acidity of their a-Hs,least acidic to most acidic: CH₃CH₂CON(CH₃)₂,PhCOCH₂CHO,CH₃CH₂CO₂CH₂CH₃,and PhCOCH₂CO₂CH₂CH₃.

Question 12

When compared to the keto form,the enol form of which of the following compounds is most stable?

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

Question 13

Which of the following compounds does not have an alpha hydrogen?

A)I
B)II
C)III
D)IV
E)all of the above

Question 14

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

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

Question 15

Which compound's α H is the least acidic?

A)nitroethane
B)propanenitrile
C)N,N-dimethylacetamide
D)propanal
E)acetone

Question 16

Why is the pKa of acetone 20 while that of ethane is 50? Explain the origin for this difference in acidity.

Question 17

List the following carbonyl compounds in order of decreasing pKa: 2,4-pentanedione,diethyl malonate,propanal,ethyl acetate.

Question 18

How many Hs in the compound below are replaced by Ds when it is shaken in D₂O containing trace hydroxide?

A)1
B)2
C)3
D)6
E)7

Question 19

Which of the labeled hydrogen atoms in the following structure is the most acidic?

A)1
B)2
C)3
D)4
E)5

Question 20

Provide a detailed,stepwise mechanism for the acid-catalyzed enolization of acetaldehyde.

Question 21

Provide the major organic product of the following.

Question 22

Give the major product for the following reaction.

A)
B)
C)
D)
E)no reaction

Question 23

What iminium salt is produced in the reaction shown below?

Question 24

Provide the major organic product of the following.

Question 25

Provide a detailed,stepwise mechanism for the formation of acetate and bromodiiodomethane from bromoacetone,hydroxide and iodine.

Question 26

Provide the major organic product of the following.

Question 27

What is the carbon nucleophile which attacks molecular bromine in the acid-catalyzed α-bromination of a ketone?

A)an enolate
B)a Grignard reagent
C)an acetylide
D)a carbocation
E)an enol

Question 28

Give the major product for the following reaction.

A)
B)
C)
D)
E)

Question 29

Which is the major organic product from the following reaction?

A)
B)
C)
D)
E)

Question 30

Which of the following methods can be used to prepare the following compound?

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

Question 31

Which of the following will alkylate a lithium enolate most rapidly?

A)methyl bromide
B)isopropyl bromide
C)neopentyl bromide
D)bromobenzene
E)2-methylbromobenzene

Question 32

The Hell-Volhard-Zelinsky reaction involves

A)the α-bromination of carboxylic acids.
B)the α-bromination of ketones.
C)the bromination of alcohols.
D)the oxidation of aldehydes to acids.
E)none of the above.

Question 33

Which of the following reagents will quantitatively convert an enolizable ketone to its enolate salt?

A)lithium hydroxide
B)lithium diisopropylamide
C)methyllithium
D)diethylamine
E)pyridine

Question 34

Give the major product for the following reaction.

A)
B)
C)
D)
E)

Question 35

A student proposed the following synthesis.Why did it fail?

A)The use of LDA results in the thermodynamic product instead of the desired kinetic product.
B)LDA is insoluble in the THF solvent so the reaction is too slow to occur at a useful rate.
C)LDA acts as a nucleophile instead of a base in its reaction with cyclohexanone.
D)The tertiary bromide is too sterically hindered to be attacked by the enolate.
E)Instead of 2-methyl-2-bromopentane,2-bromo-3-methylpentane should have been used to anticipate a cationic rearrangement that would occur.

Question 36

How would you accomplish the following conversion?

A)H⁺/H₂O; HC N
B)(^-OH/NaC N)
C)Br₂/H⁺,H₂O; NaC N
D)HBr; NaC N
E)LiAlH₄; HC N; KMnO₄

Question 37

What is the major organic product of the following reaction?

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

Question 38

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

A)propanal
B)2-pentanone
C)3-pentanone
D)benzophenone
E)cyclohexanone

Question 39

Provide a detailed,stepwise mechanism for the α-bromination of acetone in base.

Question 40

Enolates are frequently formed by treating an aldehyde or ketone with LDA.However,the LDA must first be generated by reacting diisopropylamine with butyllithium.Why don't chemists just use butyllithium itself to deprotonate the aldehyde or ketone and form the enolate?

Question 41

In the Michael reaction,addition to the α,β-unsaturated carbonyl occurs in a

A)1,2-fashion
B)1,3-fashion
C)1,4-fashion
D)1,5-fashion
E)Diels-Alder reaction

Question 42

Give the major product for the following reaction.

Question 43

An enolate attacks an aldehyde and the resulting product is subsequently protonated.What type of reaction is this?

A)a Fischer esterification
B)an acid-catalyzed aldol condensation
C)a base-mediated aldol condensation
D)a Hell-Volhard-Zelinsky reaction
E)a Selman-Jones reaction

Question 44

Show how an enolate can add to a carbonyl.

Question 45

Give the major product for the reaction.

A)
B)
C)
D)
E)

Question 46

What is the major organic product of the following reaction?

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

Question 47

Provide the major organic product(s)of the reaction shown below.

Question 48

What is the major organic product of the following aldol addition?

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

Question 49

What is the major organic product from the following reaction?

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

Question 50

Give the major product for the following reaction.

Question 51

What is the molecular formula of the major organic product of the following reaction sequence?

A)C₇H₁₂O
B)C₇H₁₄O
C)C₁₁H₁₉N
D)C₁₁H₂₁N
E)C₁₁H₂₃N

Question 52

Which of the following statements describes the first step in the mechanism of the aldol condensation?

A)An alpha hydrogen is abstracted by the base to form an enolate anion.
B)A nucleophilic base attacks the carbonyl carbon atom.
C)The carbonyl oxygen is protonated by the base ion.
D)The alpha hydrogen is abstracted by an acid to the enolate anion.
E)The carbonyl oxygen of one aldehyde attacks the carbonyl carbon of another.

Question 53

Give the major product for the following reaction.

A)
B)
C)
D)
E)

Question 54

Give the major product for the following reaction.

Question 55

Give the major product for the following reaction.

Question 56

Give the major product for the following reaction.

Question 57

Give the major product for the following reaction.

A)
B)
C)
D)
E)

Question 58

Provide the major organic product(s)of the reaction shown below.

Question 59

Which of the following aldehydes does not undergo an aldol addition when mixed with base?

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

Question 60

Give the major product for the reaction.

A)
B)
C)
D)
E)

Question 61

Provide the structure of the Claisen product in the self-condensation of methyl phenylacetate.

Question 62

What materials are needed to prepare the following product?

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

Question 63

What is the major product of the following condensation?

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

Question 64

Give the major product for the following reaction.

Question 65

What two molecules were condensed in an aldol reaction to produce PhCH CHCOPh?

Question 66

What two starting materials yield OHCCH₂CO₂CH₂CH₃ as the mixed Claisen condensation product?

Question 67

What two molecules were condensed in an aldol reaction to produce
(CH₃)₃CCH CHCOCH₃?

Question 68

Show how the compound below could be prepared by a synthetic route that uses a Claisen condensation.

Question 69

Provide the major organic product(s)of the reaction shown below.

Question 70

Which of the following could result from the dehydration of an aldol?

A)4-methyl-3-penten-2-one
B)4-methyl-4-penten-2-one
C)4-methyl-5-hexen-2-one
D)4-methyl-4-hexen-2-one
E)3-methyl-4-penten-2-one

Question 71

Provide a synthesis of 2-ethylhexanol using butanal as the only source of carbon.

Question 72

Give the major product of the following reaction.

Question 73

What is the major organic product of the following addition?

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

Question 74

Give the major product for the following reaction.

Question 75

Provide the structure of the major organic product that results when 4-methylhexanal is heated in base and undergoes and aldol addition followed by a dehydration.

Question 76

(a)The base-catalyzed reaction of 1 mole of acetone with 2 moles of benzaldehyde yields a yellow solid,C₁₇H₁₄O.What is the structure of the product?
(b)What will be the result when only 1 mole of benzaldehyde is added?
(c)What will be the result when acetone is not added at all?
(d)What will be the result when benzaldehyde is not added at all?
(e)Why is the self-condensation of acetone unlikely in the presence of benzaldehyde?

Question 77

Propose a stepwise mechanism that would explain the following conversion.

Question 78

Give the major product of the following reaction.

A)
B)
C)
D)
E)

Question 79

Give the major product for the following reaction.

A)
B)
C)
D)
E)

Question 80

In theory a poorly planned crossed aldol reaction can produce how many different aldol regioisomers?

A)1
B)2
C)3
D)4
E)5