Deck 8: Ð Bonds As Nucleophiles

Question 1

In the electrophilic addition of HBr to an alkene,what does the pi bond act as?

A)a nucleophile
B)an electrophile
C)a leaving group
D)a Lewis acida

Answer 1

a nucleophile

Question 2

What is the driving force for the brominium ion formation in the addition of Br₂ to an alkene?

A)Bromine is more electronegative than carbon and can thus better handle the positive charge.
B)The positively charged bromine has a full octet,whereas the positively charged carbon does not.
C)The cyclic structure of the brominium ion introduces added stability over the straight chain form.
D)The carbocation structure is not capable of hyperconjugation,whereas the bromonium ion is capable of hyperconjugation.

Answer 2

The positively charged bromine has a full octet,whereas the positively charged carbon does not.

Question 3

Which of the following reaction conditions would achieve the transformation shown below?

A)H₂O,H₂SO₄
B)1)Hg(OAc)₂,H₂O 2)NaBH₄
C)1)BH₃ 2)H₂O₂,NaOH,H₂O
D)1)mCPBA 2)H⁺,H₂O

Answer 3

1)BH₃ 2)H₂O₂,NaOH,H₂O

Question 4

What is the major product of the following reaction?

A)
B)
C)
D)

Question 5

What sort of intermediate leads to the regiochemistry observed in the addition of hydrobromic acid to an alkene?

A)carbocation
B)bromonium ion
C)carbene
D)bromide

Question 6

What sort of stereoselectivity is attained upon the addition of bromine to an alkene?

A)Markovnikov
B)anti-Markovnikov
C)syn
D)anti

Question 7

What is (are)the product(s)of the following electrophilic addition?

A)
B)
C)
D)

Question 8

What would be the major product of the following reaction performed under kinetic conditions?

A)
B)
C)
D)

Question 9

What is the hybridization of the positively charged carbon in the carbocation showed below?

A)S
B)Sp
C)sp²
D)sp³

Question 10

What sort of regiochemistry is attained upon the addition of water to an alkene by oxymercuration-demurcuration?

A)Markovnikov
B)anti-Markovnikov
C)syn
D)anti

Question 11

What is(are)the product(s)of the following electrophilic addition?

A)
B)
C)
D)

Question 12

Identify the kinetic and thermodynamic products of the following reaction:

A)kinetic: thermodynamic:

B)kinetic: thermodynamic:

C)kinetic: thermodynamic:

D)kinetic:

Question 13

Consider the two carbocations shown below.Which is more stable and why?

A)I because of sterics
B)I because of hyperconjugation
C)II because of sterics
D)II because of hyperconjugation

Question 14

Which product would be expected in the hydrogenation of 3-methylhept-3-ene with excess hydrogen gas using a palladium catalyst?

A)(R)-3-methylheptane
B)(S)-3-methylheptane
C)racemic 3-methylheptane
D)No reaction would occur.c

Question 15

Which of the following reaction conditions would achieve the transformation shown below?

A)Br₂,H₂O
B)1)mCPBA 2)NaBr,NH₄Cl,H₂O
C)1)BH₃,H₂O₂ 2)Br₂
D)NaBr,NH₄Cl,H₂O

Question 16

How many stereoisomers would be expected to form given the following halohydrin reaction?

A)1
B)2
C)4
D)8

Question 17

What type of bonds comprise a carbon-carbon double bond?

A)two sigma bonds
B)two pi bonds
C)one sigma and one pi bond
D)one pi bond

Question 18

Which of the following represents the most stable carbocation?

A)
B)
C)
D)

Question 19

What sort of regiochemistry is attained upon the acid catalyzed addition of water to an alkene?

A)Markovnikov
B)anti-Markovnikov
C)syn
D)anti

Question 20

In the addition of bromine to an alkene,how does the bromonium ion behave?

A)as a Brønsted acid
B)as a Brønsted base
C)as a nucleophile
D)as an electrophile

Question 21

How many stereoisomers would be expected to form given the following epoxide ring opening reaction?

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

Question 22

Which of the following reaction conditions would achieve the transformation shown below?

A)H₂O,H₂SO₄
B)1)Hg(OAc)₂,H₂O 2)NaBH₄
C)1)BH₃ 2)H₂O₂,NaOH,H₂O
D)H₂O,NaOH

Question 23

If deuterated borane were used instead of borane in the hydroboration oxidation of the alkene shown below,what would be the expected product? (D = ²H)

A)
B)
C)
D)

Question 24

What would the major product of the following reaction be?

A)
B)
C)
D)a racemic mixture of

Question 25

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

A)
B)
C)
D)

Question 26

What would be the expected product(s)for the following transformation?

A)
B)
C)No reaction would occur.
D)A 50:50 mixture of

Question 27

Which of the following best describes the formation of an epoxide from cyclopentene with mCPBA?

A)stereoselective
B)stereospecific
C)regioselective
D)regiospecific

Question 28

In the following base catalyzed epoxide ring opening reaction,which stereoisomer do you expect to be the major product?

A)
B)
C)
D)

Question 29

Which of the following best represents the transition state leading to the first intermediate in the following hydroboration oxidation reaction?

A)
B)
C)
D)

Question 30

Which of the two products shown below would be expected to be the major product and why?

A)I because of resonance stabilization by the oxygen lone pairs
B)I because of induction from the oxygen atom
C)II because of induction from the oxygen atom
D)II because of resonance stabilization by the oxygen lone pairs

Question 31

Which of the following best describes a stereoselective reaction?

A)a reaction where one stereoisomer is produced more than another
B)a reaction that exclusively produced only one enantiomer
C)a reaction that forms a stereocentre
D)a reaction that involves a chiral reactant

Question 32

Which of the following best describes the product of the hydroboration oxidation of an alkene?

A)syn addition and Markovnikov
B)anti addition and Markovnikov
C)syn addition and anti-Markovnikov
D)anti addition and anti-Markovnikov

Question 33

What would be the expected product from the reaction shown below?

A)
B)
C)
D)

Question 34

What would be the expected product for the epoxidation of but-2-ene (shown below)?

A)
B)
C)
D)

Question 35

Which of the following statements best defines the Hammond postulate?

A)The kinetic pathway is the pathway with the lowest energy transition state.
B)The rate of a reaction depends entirely on the activation energy barrier.
C)The structure of an intermediate most resembles the species nearest to it in energy.
D)The structure of a transition state most resembles the species nearest to it in energy.

Question 36

What sort of selectivity would be achieved from the reaction shown below?

A)stereoselectivity
B)regioselectivity
C)stereoselectivity and regioselectivity
D)no selectivity

Question 37

Which of the following electrophilic addition reactions is both regioselective and stereoselective?

A)oxymercuration-demercuration
B)hydroboration oxidation
C)hydrogen halide addition
D)halogen addition

Question 38

What would be expected to be the major product under the reaction conditions shown below?

A)
B)
C)
D)

Question 39

Why are reactions involving a carbocation intermediate considered NOT stereoselective?

A)Carbocations can undergo carbocation rearrangements,leading to a mixture of stereoisomers.
B)Carbocations are highly reactive,resulting in a loss of stereoselectivity.
C)The newly formed empty p orbital is accessible above and below the plane of the molecule.
D)All carbocations are achiral molecules.

Question 40

What would be the expected product from the reaction shown below?

A)
B)
C)
D)

Question 41

What kind of product would result from the reduction of an internal alkyne using hydrogen gas and Lindlar's catalyst?

A)a product with trans- stereochemistry
B)a product with cis- stereochemistry
C)a product with anti- stereochemistry
D)no stereochemistry

Question 42

Why is anti-Markovnikov regiochemistry primarily observed in hydroboration oxidation of alkenes?

A)It is a result of the kinetic pathway.
B)It is a result of the thermodynamic pathway.
C)The reaction uses boron's empty p-orbitals instead of an empty carbocation p-orbital.
D)The first step in the mechanism is concerted.

Question 43

Which of the following best describes the formation of an alcohol from an alkene using either oxomercuration or acid-catalyzed hydrolysis?

A)Both result in a Markovnikov product.
B)Both are susceptible to carbocation rearrangements.
C)Both are stereoselective.
D)Neither are regioselective.

Question 44

A reaction that produces a chiral product is considered stereoselective.

Question 45

Addition of bromine to an alkene leads to a Markovnikov product.

Question 46

All electrophilic addition reactions to alkenes are regioselective.

Question 47

What would be the kinetic product of one equivalent of water reacting with 4-methylhex-1,4-diene under acidic conditions?

A)4-methylhex-1,4-diol
B)4-methylhex-1-en-4-ol
C)4-methylhex-4-en-1-ol
D)3-methylhex-5-en-3-ol

Question 48

Markovnikov regiochemistry is a result of both carbocation stability and sterics.

Question 49

A secondary carbocation neighbouring a tertiary carbon is at risk for carbocation rearrangements.

Question 50

Hydrogenation of an alkene using palladium as a catalyst results in syn addition.

Question 51

The reaction of a terminal alkyne with Hg(AcO)₂ results in an aldehyde.

Question 52

Hydroboration-oxidation of alkenes results in anti-Markovnikov stereochemistry.

Question 53

What would be the expected product of one equivalent of bromine with 3-methybutyne?

A)
B)
C)
D)

Question 54

Which of the following is observed in the hydrogenation of an alkene in the presence of a palladium catalyst?

A)Markovnikov addition
B)anti-Markovnikov addition
C)syn addition
D)anti addition

Question 55

In electrophilic addition reactions to alkenes,the ð electrons act as an electrophile.

Question 56

Which of the following would be an expected intermediate under the reaction conditions shown below?

A)
B)
C)
D)

Question 57

What would be the expected product or products of (R)-3-chlorobut-1-ene with HBr?

A)(2R,3R)2-bromo-3-chlorobutane
B)(2S,3R)2-bromo-3-chlorobutane
C)a diastereomeric mixture of (2R,3R)2-bromo-3-chlorobutane and (2S,3R)2-bromo-3-chlorobutane
D)meso 2-bromo-3-chlorobutane

Question 58

Which of the following alkenes would react the quickest in the presence of sulfuric acid and water?

A)
B)
C)
D)

Question 59

Hydroboration-oxidation of an alkene results in syn addition.
8

Question 60

How many carbons are part of the conjugated system in the molecule shown below?

A)6
B)7
C)13
D)15

Question 61

The reaction of an internal alkyne with BH(cy)₂ results in an aldehyde.

Question 62

Hydrogenation of an alkyne with Lindlar's catalyst results in a saturated product.

Question 63

Oxymercuration-demercuration of alkenes are at risk of carbocation rearrangements.

Question 64

Conjugation leads to stabilization of carbocations through induction.

Question 65

Carbocations formed in electrophilic addition reactions are_______________ hybridized.

Question 66

Alkynes can be converted to alcohols with two equivalents of water.

Question 67

Reactions involving a carbocation intermediate are not stereoselective.

Question 68

Acid catalyzed hydration of (S)-4-methylpent-1-ene results in the formation of alcohols that are enantiomers of each other.

Question 69

Hydrolysis of a bromonium leads to a product with anti-stereoselectivity.

Question 70

Reactions going through the more stable carbocation result in _______________ regiochemistry.

Question 71

The first step in the mechanism of bromine addition to an alkene is a(n)_______________ step.

Question 72

Conjugated alkenes form stable carbocations in addition reactions,leading to slower reaction rates.

Question 73

Epoxides can be hydrolyzed in the presence of both base and acid.

Question 74

Hydrogenation of an alkyne with Lindlar's catalyst results in a product with cis stereochemistry.

Question 75

Hydrogen bromide addition to an alkyne goes through a carbocation intermediate.

Question 76

The product that forms fastest is considered the _______________ product.

Question 77

Reacting an alkyne with only one equivalent of hydrogen gas in the presence of a palladium catalyst results in an alkene as a primary product.

Question 78

Addition of atoms to the same face of an alkene is an example of regioselectivity.

Question 79

A carbocation is an example of a Lewis acid.

Question 80

Acid hydrolysis of an epoxide results in anti-addition.