Deck 18: Selectivity and Reactivity in Enolate Reactions

Question 1

What is the product of the reaction shown below?

A)
B)
C)
D)

Answer 1

Question 2

Which of the following best describes the transition state structures shown below?

A)I is favoured because R₁ and R₃ are trans.
B)I is favoured because R₁ and R₃ are cis.
C)II is favoured because R₁ and R₃ are trans.
D)II is favoured because R₁ and R₃ are cis.

Answer 2

I is favoured because R₁ and R₃ are trans.

Question 3

Which of the following best categorizes sites (a)and (b)in the aldehyde shown below?

A)(a)and (b)are both nucleophilic sites.
B)(a)and (b)are both electrophilic sites.
C)(a)is a nucleophilic site,and (b)is an electrophilic site.
D)(a)is an electrophilic site,and (b)is a nucleophilic site.

Answer 3

(a)is a nucleophilic site,and (b)is an electrophilic site.

Question 4

What is the product of the transformation shown below?

A)
B)
C)
D)

Question 5

What is the role of titanium chloride in the Mukaiyama reaction shown below?

A)Titanium activates the aldehyde electrophile,and a chloride ion removes the sialyl-containing TMS group.
B)Titanium activates the alkene electrophile,and a chloride ion removes the sialyl-containing TMS group.
C)Titanium activates the aldehyde electrophile,and a chloride ion forms an ion pair with the carbocation intermediate.
D)Titanium removes the sialyl-containing TMS group,and the chloride ion activates the aldehyde nucleophile.

Question 6

Which of the following represents an umpolung electrophile?

A)
B)
C)
D)

Question 7

Which of the following best describes the product of the reaction shown below?

A)It is the kinetic product,which is favoured under low temperatures.
B)It is the thermodynamic product,which is favoured under low temperatures.
C)It is the kinetic product,which is favoured under high temperatures.
D)It is the thermodynamic product,which is favoured under high temperatures.

Question 8

Which of the following best describes the stereochemistry of the products in an aldol reaction?

A)E and Z enolates favour syn-aldols.
B)Z and Z enolates favour anti-aldols.
C)E enolates favour syn-aldols,and Z enolates favour anti-aldols.
D)E enolates favour anti-aldols,and Z enolates favour syn-aldols.

Question 9

Which of the following best describes an enolate and an á,â unsaturated carbonyl in a Michaels addition?

A)The enolate and the á,â unsaturated carbonyl are both Michaels donors.
B)The enolate and the á,â unsaturated carbonyl are both Michaels acceptors.
C)The enolate is a Michaels acceptor and the á,â unsaturated carbonyl is Michaels donor.
D)The enolate is a Michaels donor and the á,â unsaturated carbonyl is Michaels acceptor.

Question 10

Which of the following best describes á,â unsaturated carbonyls?

A)They are nucleophilic and conjugated.
B)They are nucleophilic and unconjugated.
C)They are electrophilic and conjugated.
D)They are electrophilic and unconjugated.

Question 11

Which of the following best describes cuprate reagents?

A)They are less nucleophilic than Grignard reagents and promote 1,4-addition of á,â-unsaturated carbonyls.
B)They are more nucleophilic than Grignard reagents and promote 1,4-addition of á,â-unsaturated carbonyls.
C)They are less nucleophilic than Grignard reagents and promote 1,2-addition of á,â-unsaturated carbonyls.
D)They are more nucleophilic than Grignard reagents and promote 1,2-addition of á,â-unsaturated carbonyls.

Question 12

What is the role of titanium chloride in the reaction shown below?

A)Lewis acid
B)Lewis base
C)Brønsted acid
D)Brønsted base

Question 13

Which of the following represents an umpolung nucleophile?

A)
B)
C)
D)

Question 14

What is the product of the transformation shown below?

A)
B)
C)
D)

Question 15

Which of the following is considered the 1,4 conjugate addition product of the reaction shown below?

A)
B)
C)
D)

Question 16

Which of the following best describes the relationship of the enolates shown below?

A)They are stereoisomers.
B)They are regioisomers.
C)They are identical molecules.
D)They are tautomers.

Question 17

Which of the following best describes the transition state shown below?

A)The aldehyde substituent is pseudo-equatorial,and it will lead to an anti-aldol.
B)The aldehyde substituent is pseudo-axial,and it will lead to an anti-aldol.
C)The aldehyde substituent is pseudo-equatorial,and it will lead to a syn-aldol.
D)The aldehyde substituent is pseudo-axial,and it will lead to a syn-aldol.

Question 18

Which of the following conditions best promotes 1,2-addition of an á,â-unsaturated carbonyl?

A)NH₃,0°
B)NH₃,100°
C)NaNH₂,0°
D)NaNH₂,100°

Question 19

What is the product of an á,â-unsaturated carbonyl with organometallic reagents?

A)Grignard and cuprate reagents lead to 1,2 direct addition.
B)Grignard and cuprate reagents lead to 1,4 conjugate addition.
C)Grignard reagents lead to 1,2 direct addition,and cuprate reagents lead to 1,4 conjugate addition.
D)Grignard reagents lead to 1,4 conjugate addition,and cuprate reagents lead to 1,2 direct addition

Question 20

Which of the following best describes the relationship between the reactant and product in the reaction shown below?

A)They are stereoisomers.
B)They are regioisomers.
C)They are constitutional isomers.
D)They are tautomers.

Question 21

What is the product of the transformation shown below?

A)
B)
C)
D)

Question 22

What is the product of the reaction shown below?

A)
B)
C)
D)

Question 23

Which set of conditions will accomplish the following transformation?

A)1)1.05 eq.LDA,inverse addition -78°C 2)Ethanal 3)H₃O⁺/heat
B)1)0.98 eq.LDA -78°C to 0°C 2)Ethanal 3)H₃O⁺/heat
C)1)1 eq.NaOMe -78°C 2)Ethanal 3)H₃O⁺/heat
D)1)1 eq.NaOMe 20°C 2)Ethanal 3)H₃O⁺/heat

Question 24

Which of the following is NOT a possible product of the reaction scheme shown below?

A)
B)
C)
D)

Question 25

What would be the major product of the reaction shown below?

A)
B)
C)
D)

Question 26

Which of the following represents the kinetic enolate of the diketone compound shown below?

A)
B)
C)
D)

Question 27

Which of the following represents the thermodynamic enolate of the diketone compound shown below?

A)
B)
C)
D)

Question 28

Which of the following is the major product of the reaction shown below?

A)
B)
C)
D)

Question 29

What would be the major product of the reaction shown below?

A)
B)
C)
D)

Question 30

What is the role of diamine in the reaction shown below?

A)nucleophilic catalyst
B)electrophilic catalyst
C)acid catalyst
D)base catalyst

Question 31

Which of the following is an intermediate of the reaction shown below?

A)
B)
C)
D)

Question 32

What set of conditions would result in the E-enolate of the ketone shown below?

A)BCy₂Cl,NEt₃
B)BBu₂Cl,i-Pr₂NEt
C)LDA,-78°C
D)NaOH

Question 33

What is the product of the reaction shown below?

A)
B)
C)
D)

Question 34

Which of the following best explains the regioselectivity of cuprate and Grignard reactions with á,â-unsaturated carbonyls?

A)Grignards are more nucleophilic than cuprates and attack the most positive carbonyl carbon.
B)Grignards are less nucleophilic than cuprates and attack the most positive carbonyl carbon.
C)Grignards are more nucleophilic than cuprates and attack the most positive vinylic carbon.
D)Grignards are less nucleophilic than cuprates and attack the most positive vinylic carbon.

Question 35

Which set of conditions will accomplish the following transformation?

A)1)1.05 eq.LDA,inverse addition -78 °C 2)Ethanal 3)H₃O⁺/heat
B)1)0.98 eq.LDA -78°C to 0°C 2)Ethanal 3)H₃O⁺/heat
C)1)1 eq.NaOMe -78°C 2)Ethanal 3)H₃O⁺/heat
D)1)1 eq.NaOMe 20°C 2)Ethanal 3)H₃O⁺/heat

Question 36

Which of the following is an appropriate synthon for the compound shown below?

A)
B)
C)
D)

Question 37

1,2 conjugate addition of an enone is considered the thermodynamic product.

Question 38

What is the major product of the reaction scheme shown below?

A)
B)
C)
D)

Question 39

What is the major product of the reaction scheme shown below?

A)
B)
C)
D)

Question 40

Which of the following represents a Umpolong synthon?

A)
B)
C)
D)

Question 41

The addition of BCy₃ to a carbonyl deprotonation reaction results in the Z enolate being favoured.

Question 42

The thermodynamic product is a result of a reaction under reversible conditions.

Question 43

Cyanohydrins can act as umpolung electrophiles.

Question 44

Strong amide bases like LDA favour the formation of Z enolates.

Question 45

Allowing a system to equilibrate promotes formation of the kinetic enolate.

Question 46

Umpolung represents the change in the reactivity of an atom.

Question 47

Consonant reactivity is the alternating reactivity pattern of consecutive atoms in a chain.

Question 48

An aldol reaction is an example of an umpolung reaction.

Question 49

E enolates favour the formation of cis aldols.

Question 50

Use of a bulky base like LDA promotes formation of the thermodynamic enolate.

Question 51

Use of LDA to depronate the á proton of an amide results in the Z enolate exclusively.

Question 52

Grignard reagents react with á,â unsaturated carbonyls to form the thermodynamic product.

Question 53

Grignard and cuprate reagents are said to have _______________ reactivity.

Question 54

The Wittig reaction favours cis stereochemistry of the resultant alkene product.

Question 55

The Grignard reagent is an example of an umpolung nucleophile.

Question 56

A stabilized ylide contains a neighbouring electron donating group.

Question 57

The thermodynamic enolate contains the more substituted alkene.

Question 58

Strong nucleophiles promote 1,2-addition over 1,4-addition.

Question 59

A ylide with an electron drawing group will result in trans geometry of the product alkene.

Question 60

A cuprate is an example of an umpolung reagent.

Question 61

Predict the structure of the product shown below.

Question 62

1,4-addition to an á,â-unsaturated carbonyl is also referred to as _______________ addition.

Question 63

A Z-enolate will form a(n)_______________ aldol product when reacted with a carbonyl.

Question 64

Molecules with oxy substituents separated by an even number of atoms display _______________ reactivity.

Question 65

The following reaction results in two enantiomers,with one of the enantiomers existing in excess.Predict which enantiomer will be the major product,and show an intermediate that influences this result.

Question 66

The kinetic enolate has the _______________ substituted double bond.

Question 67

Draw a mechanism of the following transformation.

Question 68

The alternating reactivity pattern of consecutive carbons on a chain attached to a carbonyl is known as a(n)_______________ reactivity pattern.

Question 69

Stabilized ylides contain a neighbouring _______________ group.

Question 70

Draw the mechanism of the following transformation.

Question 71

What are the reactants of the Robinson annulation product shown below?

Question 72

The reaction of a cuprate with an á,â unsaturated carbonyl results in_______________ addition.

Question 73

Deprotonation of the á proton of an amide results in the _______________.

Question 74

Inversion of the expected reactivity of an atom is known as _______________ reactivity.

Question 75

What is the product of the following reaction scheme?

Question 76

The following reaction results in a cyclic product.What is the product,and show a mechanism for the following reaction.