Deck 12: Formation of Ð Bonds by Elimination Processes

Question 1

What would be the product of the reaction shown below?

A)
B)
C)
D)

Answer 1

Question 2

Which of the following reagents would achieve the transformation shown below?

A)PCC,CH₂Cl₂
B)Na₂Cr₂O₇,H₂SO₄
C)CrO₃,H₂SO₄
D)H₃O⁺

Answer 2

PCC,CH₂Cl₂

Question 3

Which of the following reaction mechanisms would you expect to dominate from the reaction and conditions shown below?

A)S_N1
B)S_N2
C)E1
D)E2

Answer 3

E2

Question 4

Which of the following reaction mechanisms would you expect to dominate from the reaction and conditions shown below?

A)S_N1
B)S_N2
C)E1
D)E2

Question 5

Which of the following best describes an E1 elimination?

A)It is unimolecular and goes through a carbocation intermediate.
B)It is unimolecular and goes through a concerted mechanism.
C)It is bimolecular and goes through a carbocation intermediate.
D)It is bimolecular and goes through a concerted mechanism.

Question 6

Which of the following statements best describes Zaitsev's rule?

A)An elimination reaction will favour the most stable product.
B)An elimination reaction will favour the most stable intermediate
C)An elimination reaction will favour the least stable product.
D)An elimination reaction will favour the least stable intermediate

Question 7

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

A)
B)
C)
D)A mixture of

Question 8

What is the Hoffman product in an elimination reaction?

A)the kinetic product using a strong unhindered base
B)the thermodynamic product using a strong unhindered base
C)the kinetic product using a strong hindered base
D)the thermodynamic product using a strong hindered base

Question 9

Which of the following best describes an E2 reaction mechanism?

A)The leaving group leaves,resulting in a carbocation,following by deprotonation of the â hydrogen and formation of a ð bond.
B)The â hydrogen is deprotonated,resulting in a carbocation,followed by loss of the leaving group and formation of a ð bond.
C)The â hydrogen is deprotonated and the leaving group leaves simultaneously,leading to the formation of a ð bond.
D)The â hydrogen is deprotonated,resulting in a carboanion,followed by loss of the leaving group and formation of a ð bond.

Question 10

Which of the following products will the E2 elimination reaction shown below lead to?

A)
B)
C)
D)

Question 11

Which of the following products will the E2 elimination reaction below lead to?

A)
B)
C)
D)

Question 12

Which of the following substrates is not suitable as an E1 substrate?

A)
B)
C)
D)

Question 13

Which of the following reaction mechanisms would you expect to dominate from the reaction and conditions shown below?

A)S_N1
B)S_N2
C)E1
D)E2

Question 14

Which of the following best describes the relationship between the leaving group and the â-hydrogen in an E2 elimination?

A)periplanar
B)antiperiplanar
C)scissile
D)enantiomeric

Question 15

Which of the following best describes an E2 elimination reaction?

A)It is unimolecular and goes through a carbocation intermediate.
B)It is unimolecular and goes through a concerted mechanism.
C)It is bimolecular and goes through a carbocation intermediate.
D)It is bimolecular and goes through a concerted mechanism.

Question 16

Which of the following compounds would be unsuitable for oxidation?

A)methanol
B)ethanol
C)2-propanol
D)2-methyl-2-propanol

Question 17

What is the first step in an E1 reaction mechanism?

A)The leaving group leaves,resulting in a carbocation.
B)The â hydrogen is deprotonated,resulting in a carbocation.
C)The â hydrogen is deprotonated and the leaving group leaves simultaneously.
D)The â hydrogen is deprotonated,resulting in a carboanion.

Question 18

Which of the following represents the first mechanistic step in the oxidation reaction shown below?

A)
B)
C)
D)

Question 19

Which of the following reaction mechanisms would you expect to dominate from the reaction and conditions shown below?

A)S_N1
B)S_N2
C)E1
D)E2

Question 20

For an E2 elimination of bromocyclohexane to occur,what must the halogen group be?

A)axial
B)equatorial
C)either axial or equatorial
D)planar

Question 21

Which of the following best describes sodium hydride?

A)It is a strong,non-nucleophilic base.
B)It is a strong,nucleophilic base.
C)It is a weak,non-nucleophilic base.
D)It is a weak,nucleophilic base.

Question 22

Which cyclohexane derivative would you expect to react faster under E2 elimination conditions and why?

A)A because its less sterically hindered
B)B because its less sterically hindered
C)A because its scissile C-H bond is antiperiplanar
D)B because its scissile C-H bond is antiperiplanar

Question 23

Which of the following reaction mechanisms would you expect to dominate from the reaction and conditions shown below?

A)S_N1
B)S_N2
C)E1
D)E2

Question 24

Which of the following reaction mechanisms would you expect to dominate from the reaction and conditions shown below?

A)S_N1
B)S_N2
C)E1
D)E2

Question 25

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

A)
B)
C)
D)

Question 26

Which of the following mechanisms are promoted by polar protic solvents?

A)S_N1 and S_N2
B)E1 and E2
C)S_N2 and E2
D)S_N1 and E1

Question 27

Which of the following best describes the Hoffman product in an elimination reaction?

A)an unhindered base giving the less substituted product
B)an unhindered base giving the more substituted product
C)a hindered base giving the less substituted product
D)a hindered base giving the more substituted product

Question 28

What is the role of Br₂ in the first step of the oxidation of alcohols?

A)nucleophile
B)electrophile
C)leaving group
D)base

Question 29

Why does the E2 mechanism require an antiperiplanar relationship between the leaving group X and the â hydrogen?

A)This conformation maximizes overlap between the C-H ó* orbital and the C-X ó orbital.
B)This staggered conformation minimizes steric repulsion.
C)This conformation maximizes overlap between the C-H ó orbital and the C-X ó* orbital.
D)This conformation leads to the more substituted alkene.

Question 30

What is the role of HCrO₃⁺ in the first step of the oxidation of alcohols?

A)proton donor
B)proton acceptor
C)nucleophile
D)electrophile

Question 31

What sort of reaction mechanism is employed in an acid catalyzed dehydration reaction?

A)S_N1
B)S_N2
C)E1
D)E2

Question 32

Which of the following substrates will undergo the fastest E1 reaction?

A)
B)
C)
D)

Question 33

What is the effect of adding heat to a reaction capable of both elimination and substitution mechanisms?

A)It pushes a reaction towards the thermodynamic elimination product.
B)It pushes a reaction towards the thermodynamic substitution product.
C)It pushes a reaction towards the kinetic elimination product.
D)It pushes a reaction towards the kinetic substitution product.

Question 34

Which of the following substrates would undergo the slowest elimination reaction?

A)
B)
C)
D)

Question 35

Which orbital interaction best describes the hyperconjugation that results in increased stability of a substituted alkene?

A)ó $\rightarrow$ ð
B)ó $\rightarrow$ ð*
C)ó* $\rightarrow$ ð*
D)ð $\rightarrow$ ð*

Question 36

Which alkene isomer of an elimination reaction is more favoured and why?

A)the E product because there is better ó - ð* overlap
B)the Z product because there is better ó - ð* overlap
C)the E product because there is less steric hindrance
D)the Z product because there is less steric hindrance

Question 37

Which of the following reaction mechanisms would you expect to dominate from the reaction and conditions shown below?

A)S_N1
B)S_N2
C)E1
D)E2

Question 38

What is the role of HCO₃^- in the first step of the oxidation of alcohols?

A)acid
B)electrophile
C)leaving group
D)base

Question 39

Which of the following best describes tert-butoxide?

A)It is a strong,bulky base.
B)It is a strong,non-bulky base.
C)It is a weak,bulky base.
D)It is a weak,non-bulky base.

Question 40

Which of the following reagents is required for a dehydration reaction and why?

A)strong acid to protonate the alcohol group
B)strong base to deprotonate the alcohol group
C)strong base to deprotonate the â hydrogen
D)strong acid to stabilize the formed carbocation

Question 41

Chromic acid oxidation of a secondary alcohol results in a carboxylic acid.

Question 42

The E alkene product is favoured because it is less sterically hindered.

Question 43

Br₂ oxidation of a primary alcohol results in an aldehyde.

Question 44

Deprotonation of the â hydrogen is the rate-limiting step in E1 eliminations.

Question 45

An E2 Elimination reaction occurs through a concerted mechanism.

Question 46

The Hoffman product is typically the result of using a bulky base.

Question 47

An E2 reaction runs faster if the scissile C-H bond is antiperiplanar.

Question 48

Dehydration reactions can proceed under an E1 or E2 mechanism.

Question 49

E2 eliminations are susceptible to carbocation rearrangements.

Question 50

Bromine acts as an electrophile in the oxidation of alcohols.

Question 51

E1 eliminations go through a carbocation intermediate.

Question 52

Heat promotes an E1 reaction over an S_N1 reaction.

Question 53

Dehydrohalogenation reactions can proceed under an E1 or E2 mechanism.

Question 54

PCC oxidation of a primary alcohol results in a carboxylic acid.

Question 55

Sodium Hydride is an example of a non-nucleophilic base.

Question 56

E2 reactions are promoted by protic solvents.

Question 57

E1 reactions are usually less stereoselective than E2 reactions.

Question 58

An E1 mechanism occurs through a single mechanistic step.

Question 59

A strong bulky nucleophile will promote an S_N2 reaction over an E2 reaction.

Question 60

Higher substituted alkenes are more stable.

Question 61

Chromic acid oxidation of a primary alcohol will result in a(n)_______________ .

Question 62

Propose a mechanism of the following reaction to generate each of the observed products.

Question 63

Zaitsev's rule states that the elimination reaction favours the most _______________ alkene product.

Question 64

Carbocation rearrangements are a possible side reaction for _______________ elimination reactions.

Question 65

The following substrate is capable of undergoing S_N1,S_N2,E1 and E2 reaction mechanisms depending on the conditions used.Suggest a set of reagents and conditions that can be used to get each reaction mechanism as the dominant mechanism.

Question 66

Predict the product of the following elimination reaction and show the mechanism using a Newman projection.

Question 67

For an E2 elimination to occur,the scissile C-H bond and the leaving group must be _______________

Question 68

Provide a set of reaction conditions to achieve the following transformation with the following major product.

Question 69

Draw the mechanism for the transformation shown below.

Question 70

The scissile C-H bond must be antiperiplanar to the leaving group in an E1 reaction.

Question 71

The less substituted alkene product of an elimination reaction is also known as the _______________ product.

Question 72

Chromic acid oxidation of a tertiary alcohol will result in _______________ .

Question 73

E1 reaction rates are dependent on the concentration of the base.

Question 74

For an E2 reaction to occur on a cyclohexyl ring,the leaving group must be in an equatorial position.

Question 75

PCC oxidation of a secondary alcohol will result in a(n)_______________ .

Question 76

In a cyclohexyl ring,the leaving group must be _______________ for an E2 reaction to occur.

Question 77

In an E2 elimination reaction,the leaving group and the scissile C-H bond are _______________ to each other.

Question 78

In hyperconjugation,the ó orbital of the C-H bond donates into the ð* orbital of the alkene.

Question 79

In an E2 mechanism,the ó orbital of the scissile C-H bond donates into the ð* bond of the leaving group.

Question 80

Dehydration reactions require the use of a(n)_______________ catalyst.