Deck 7: Ð Bonds As Electrophiles

Question 1

What is the hybridization of the intermediate in the following reaction?

A)sp
B)sp²
C)sp³
D)s

Answer 1

sp³

Question 2

Which of the following best describes the carbon bound to magnesium in a Grignard reagent?

A)electropositive and nucleophilic
B)electropositive and electrophilic
C)electronegative and nucleophilic
D)electronegative and electrophilic

Answer 2

electronegative and nucleophilic

Question 3

What does a nucleophilic attack on a carbonyl by a hydride result in?

A)ether
B)alcohol
C)ketone
D)carboxylic acid

Answer 3

alcohol

Question 4

Which reaction scheme would accomplish the transformation shown below?

A)1)MgBrMe,Et₂O 2)D₂O
B)D₂O
C)NaBD₄,EtOH
D)NaBH₄,EtOD

Question 5

What is the functional group shown below?

A)amine
B)imine
C)enamine
D)nitrile

Question 6

What is the product of the following reaction (D = deuterium,an isotope of hydrogen)?

A)
B)
C)
D)

Question 7

What is the electrophilic reactant B in the following reaction scheme?

A)
B)
C)
D)

Question 8

Which of the following best describes a carbonyl ð bond?

A)The atoms are sp² hybridized and the ð bond is parallel to the plane of the carbonyl atoms.
B)The atoms are sp² hybridized and the ð bond is perpendicular to the plane of the carbonyl atoms.
C)The atoms are sp³ hybridized and the ð bond is parallel to the plane of the carbonyl atoms.
D)The atoms are sp³ hybridized and the ð bond is perpendicular to the plane of the carbonyl atoms.

Question 9

Which resonance state contributes most to the observed electrophilic reactivity of imines?

A)the imine,because it's the most stable resonance form
B)the imine,because the positive site contains a complete octet
C)the carbocation,because it's the least stable resonance form
D)the carbocation,because the positive site contains an open p orbital

Question 10

What is the role of ethanol in the following reaction?

A)to activate the sodium borohydride reagent
B)to act solely as a solvent
C)to protonate the alkoxide formed during the reaction
D)to act as a nucleophile

Question 11

Which of the following best describes the carbon atom in a carbonyl functional group?

A)It is electrophilic and has a partial positive charge.
B)It is electrophilic and has a partial negative charge.
C)It is nucleophilic and has a partial positive charge.
D)It is nucleophilic and has a partial negative charge.

Question 12

Which resonance is more heavily favoured and why?

A)the oxocarbenium ion,because ð bonds are more stable than lone pairs
B)the oxocarbenium ion,because all atoms have a full octet
C)the carbocation,because the positive charge is on the least electronegative atom
D)the carbocation,because lone pair electrons are more stable than ð bonds

Question 13

Which functional group is more reactive as an electrophile and why?

A)Aldehydes are more reactive electrophiles because they experience more electron induction from neighbouring alkyl chains.
B)Aldehydes are more reactive electrophiles because they experience less electron induction from neighbouring alkyl chains.
C)Ketones are more reactive electrophiles because they experience more electron induction from neighbouring alkyl chains.
D)Ketones are more reactive electrophiles because they experience less electron induction from neighbouring alkyl chains.

Question 14

Which of the following best describes the reduction of a ketone to an alcohol by lithium aluminum hydride (LiAlH₄)?

A)A hydride nucleophile attacks the carbonyl carbon,followed by electrostatic stabilization of the alkoxide oxygen by lithium,followed by acidic protonation of the alkoxide.
B)Lithium aluminum hydride transfers a hydrogen to both the carbonyl carbon and oxygen,resulting in an alcohol.
C)A hydride nucleophile attacks the carbonyl carbon,followed by nucleophilic attack of AlH₃ by the generated alkoxide,followed by acidic or basic conversion of the alkoyxaluminum hydride product to an alcohol.
D)Acidic protonation of the carbonyl,followed by neutralization of charge by the ð electrons,followed by nucleophilic attack by hydride.

Question 15

In the following Grignard reaction,what are the nucleophilic and electrophilic sites?

A)A is electrophilic;D is nucleophilic
B)A is nucleophilic;C is electrophilic
C)B is nucleophilic;C is electrophilic
D)B is electrophilic;D is nucleophilic

Question 16

Why is the oxocarbenium ion the more stabilized resonance state?

A)because oxygen is more electronegative than carbon and prefers to carry the charge as a result
B)because oxygen is more electronegative than carbon and prefers ð bonds as a result
C)because all atoms have a full octet in this resonance state
D)because ketones are more stable than ethers

Question 17

What is the product of the following reaction (D = deuterium,an isotope of hydrogen)?

A)
B)
C)
D)

Question 18

What is the electrophilic reactant A in the following reaction scheme?

A)
B)
C)
D)

Question 19

What is the expected product of the following transformation?

A)
B)
C)
D)

Question 20

What is the product of the following transformation?

A)
B)
C)
D)

Question 21

What would be the most likely product from the reaction scheme below?

A)
B)
C)
D)

Question 22

Which of the following molecules will undergo intramolecular hemiacetal formation under acidic conditions the fastest?

A)
B)
C)
D)

Question 23

What is the expected major product of the following transformation?

A)
B)
C)
D)

Question 24

What is a major difference between acid and base catalyzed hydration of a carbonyl?

A)Base deprotonates water and acid protonates the carbonyl in the first step of the mechanism.
B)Base deprotonates water and acid protonates the alkoxide in the second step of the mechanism.
C)Base deprotonates the carbonyl and acid protonates water in the first step of the mechanism.
D)Base deprotonates the carbonyl and acid protonates water in the second step of the mechanism.

Question 25

Which orbital of a carbonyl group accepts electrons from an incoming nucleophile?

A)ó
B)ð
C)ð*
D)ó*

Question 26

What would be the most likely product from the reaction scheme below?

A)
B)
C)
D)

Question 27

What is the role of acid in the following reaction?

A)to protonate the negatively charged cyanide
B)to stabilize the ketone
C)to protonate the formed alkoxide
D)to form hydrogen bonds with the nitrogen in the cyanide ion

Question 28

Which molecule would undergo the fastest reduction with sodium borohydride (NaBH₄)and why?

A) because it is the least sterically hindered
B) because it is the least sterically hindered
C) because it contains the most electropositive carbonyl due to induction
D)

Question 29

What is the functional group shown below?

A)amine
B)imine
C)enamine
D)nitrile

Question 30

Which of the following best describes the formation of a hemiacetal?

A)The presence of an acid speeds up the rate of formation on a hemiacetal,whereas the presence of a base has no influence in the rate of formation of a hemiacetal.
B)The presence of an acid has no influence in the rate of formation on a hemiacetal,whereas the presence of a base speeds up the rate of formation of a hemiacetal.
C)Both the presence of an acid and a base speed up the rate of formation on a hemiacetal.
D)The presence of either an acid or a base have no influence in the rate of formation of a hemiacetal.

Question 31

Which of the following reactants would most readily form an aldehyde under basic conditions?

A)
B)
C)
D)

Question 32

Which of the following best describes the nucleophilic attack of a carbonyl?

A)The nucleophile donates electrons into the LUMO of an electrophile,which is the ð* orbital.
B)The nucleophile donates electrons into the LUMO of an electrophile,which is the ó* orbital.
C)The nucleophile donates electrons into the HOMO of an electrophile,which is the ð* orbital.
D)The nucleophile donates electrons into the HOMO of an electrophile,which is the ó* orbital.

Question 33

Which reagent best reduces an imine to an amine and why?

A)NaBH₄ because it contains the most nucleophilic hydride
B)NaBH₄ because it is unreactive with acid
C)NaCNBH₃ because it contains the most nucleophilic hydride
D)NaCNBH₃ because it is unreactive with acid

Question 34

What would be the most likely product from the reaction scheme below?

A)
B)
C)
D)

Question 35

Consider the following equilibrium of a ketone hydration shown below.Which reactant would have the largest equilibrium constant for this reaction?

A)
B)
C)
D)

Question 36

What is the expected major product of the following transformation?

A)
B)
C)
D)

Question 37

What is the functional group shown below?

A)ether
B)alcohol
C)acetal
D)hemiacetal

Question 38

Considering the cyanide ion CN^-,which atom acts as a nucleophile and why?

A)carbon because it bears the only lone pair
B)nitrogen because it bears the only lone pair
C)carbon because it has a formal charge of -1
D)nitrogen because it has a formal charge of -1

Question 39

What are the partial charges at each site shown?

A)A: ä⁺ B: ä^- C: ä⁺ D:ä^-
B)A: ä⁺ B: ä^- C: ä^- D:ä⁺
C)A: ä^- B: ä⁺ C: ä⁺ D:ä^-
D)A: ä^- B: ä⁺ C: ä^- D:ä⁺

Question 40

Which of the following molecules will undergo intramolecular hemiacetal formation under acidic conditions the fastest?

A)
B)
C)
D)

Question 41

An aldehyde functional group is more oxidized than an alcohol functional group.

Question 42

An imine functional group is more oxidized than a ketone functional group.

Question 43

What is the product of the following transformation?

A)
B)
C)
D)

Question 44

A leaving group always takes a pair of electrons.

Question 45

Which of the following best represents the change in oxidation state from reactant to product in the transformation below?

A)It increases.
B)It decreases.
C)There is no change.
D)There is not enough information to determine change.

Question 46

Grignard reagents are prepared from elemental magnesium and an alkyl halide.

Question 47

Which of the following best represents the change in oxidation state from reactant to product in the transformation below?

A)It increases.
B)It decreases.
C)There is no change.
D)There is not enough information to determine change.

Question 48

Sodium borohydride reductions of aldehydes can be performed in protic solvents.

Question 49

Good leaving groups tend to be strong bases.

Question 50

Aldehydes form hydrates faster than ketones.

Question 51

The carbonyl ð* orbital accepts electrons from the incoming nucleophile.

Question 52

Which of the following statements best reflects the roles of acids and bases in the catalysis of carbonyl reactions?

A)Acids activate nucleophiles;bases activate electrophiles.
B)Acids activate electrophiles;bases activate nucleophiles.
C)Acids and bases both activate nucleophiles.
D)Acids and bases both activate electrophiles.

Question 53

Which of the following molecules represents the most oxidized state?

A)
B)
C)
D)

Question 54

Basic conditions are required for the reduction of an imine to an amine using sodium cyanoborohydride.

Question 55

Which of the following best represents the change in oxidation state from reactant to product in the transformation below?

A)It increases.
B)It decreases.
C)There is no change.
D)There is not enough information to determine change.

Question 56

Protonation of an imine makes it a better electrophile.

Question 57

Lithium aluminum hydride reductions of ketones can be performed in protic solvents.

Question 58

Acetylides act as electrophiles in the presence of a ketone.

Question 59

Grignard reactions are performed in ethereal solutions.

Question 60

Grignard reagents act as nucleophiles in the presence of water.

Question 61

Positively charged imines are worse electrophiles than neutral imines.

Question 62

Nucleophilic attack of a nitrile on a carbonyl results in a(n)_______________ .

Question 63

Lithium aluminum hydride is more reactive than sodium borohydride.

Question 64

The LUMO orbital in the carbonyl bond is the _______________ .

Question 65

Aldehydes are in fast equilibrium with their hydrated form in aqueous solution.

Question 66

The nucleophilic attack of an alcohol on a ketone in acidic conditions forms a(n)_______________ .

Question 67

A ketone must contain neighbouring electron withdrawing CF₃ groups for a hydrate to form.

Question 68

Acid acts to protonate the alkoxide in the cyanohydrin formation reaction.

Question 69

Neighbouring _______________ groups shift the equilibrium from ketones towards hydrates.

Question 70

One molecule of lithium aluminum hydride can react with up to four carbonyl groups.

Question 71

Going from a ketone to an alcohol is an example of a(n)_______________ reaction.

Question 72

Grignard reagents are compatible with all functional groups.

Question 73

Intramolecular reactions occur most readily when they form _______________ membered rings.

Question 74

Hydrogen acts as a nucleophile in borohydride since it is less electronegative than boron.

Question 75

Lithium aluminum hydride is _______________ reactive then sodium borohydride.

Question 76

Aldehydes are less electrophilic than ketones.

Question 77

_______________ is used in lieu of NaBH₄ to reduce imines.

Question 78

Intramolecular reactions are favoured when five- and six-membered rings are formed.

Question 79

Aldehydes form hydrates in aqueous solution whereas ketones do not.

Question 80

The Grignard reagents acts as a(n)_______________ in its reaction with a carbonyl.