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Organic Chemistry > Elimination Reaction > Flashcards

Elimination Reaction Flashcards

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1
Q

In an ___________ reaction a proton from the Beta position is removed with the leaving group to form a double bond

A

Elimination

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2
Q

The product of an elimination reaction will always have a ________ & be a _________

A

Double bond, alkene

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3
Q

Alkenes are named the same way as alkanes but end in _______

A

“ene”

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4
Q

When naming alkenes have to make sure what?

A

That the longest parent chain includes the double bond & that the double bond has the lowest possible number

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5
Q

Alkenes are also classified by their _______________

A

Degree of substitution

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6
Q

Degree of Substitution

A

Refers to the number of akyl groups connected to a double bond (Monosubstituted - tetrasubstituted)

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7
Q

Bredt’s Rule

A

States that its not possible for a bridgehead carbon of a bicyclic compound to have a double bond if it involves a trans configuration in a small ring

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8
Q

Bridge bicyclic compounds can only have a double bond at a bridgehead position if one of the rings has at least ___________

A

Eight Carbons

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9
Q

Cis & Trans is used to compare ______ similar group on a carbon where E & Z is used when comparing _______

A

One, two or more

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10
Q

Cis alkenes are __________ than trans alkenes because it experience steric strain from being on the same plane

A

Less stable

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11
Q

Alkenes are more stable when they are _____________

A

High substituted like tetrasubstituted alkenes

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12
Q

____________ are products of an elimination reaction

A

Alkenes

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13
Q

What are the two core steps in an elimination reaction ?

A
  1. Proton Transfer
  2. Loss of leaving group
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14
Q

In a ___________ a base takes a proton & the leaving group leaves at the same time

A

Concerted Reaction

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15
Q

In a ______________ 1st the leaving group leaves & then the base takes a proton

A

Stepwise reaction

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16
Q

The ______ mechanism is the concerted reaction

A

E2

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17
Q

How is an E2 reaction similar to SN2 reactions?

A

Its biomolecular where the rate law is R =k [substrate][base] (rate depends on both the substrate & base)

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18
Q

__________ substrates favors E2 reactions because with steric hindrance it prevents a reagent from functioning as a nucleophile (like in SN2) at a fast rate but the reagent can still function as a base (E2) without encountering much steric hindrance

A

Tertiary Substrates

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19
Q

The Ea in an E2 reaction is smallest with ________ substrate & largest with primary substrate because its least favored

A

Tertiary

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20
Q

Regiochemistry

A

When the beta (β) position aren’t identical (one may be on a methyl the other may be on an ethyl) which will result in multiple products being formed where the more substituted one is the major one

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21
Q

The more susbtituted product (the major product) is called what?

A

Zaitsev product

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22
Q

Hofman product

A

The less substitutted alkene (minor product)

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23
Q

When stereically hindered bases are used in an E2 reaction the ___________ is the major product

A

Hofman product (A base can be used to control the product of an E2 reaction)

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24
Q

When there are two stereoisomer (cis or trans) as the product in an E2 reaction then the _______ will be the major product

A

Trans

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25
Q

Coplanar

A

When the atoms are on the same plane

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26
Q

Anti-coplanar (anti-periplanar)

A

Forms a staggered newman projection

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27
Q

Syn-coplanar (Syn-periplanar)

A

Forms an eclipsed newman projection

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28
Q

E2 reaction has to be in ____________ conformation to react

A

Anti-periplanar (Anti-coplanar) (Dihedral angle of 180°)

29
Q

In a stereoselective E2 reaction

A

The substrate can produce two stereoisomeric products (Either cis or trans)

30
Q

In a stereospecific E2 reaction

A

The substrate is stereoisomeric & the stereochemical product is dependent on which stereoisomeric is used

31
Q

An E2 reaction occurs by a ____________ conformation

A

Anti-periplanar

32
Q

For an E2 reaction to occur with a cyclohexane chair conformation the leaving group must be on the _________ position to be anti-periplanar & react

A

Axial position

33
Q

E2 reaction can only happen with cylcohexanes (or any rings) when the leaving group & beta hydrogens are on ___________

A

Opposite planes (If the LG is on a wedge then the Beta hydrogens has to be on a dash to form the anti-periplanar to react)

34
Q

The _______ mechanism is the stepwise reaction

A

E1

35
Q

What is the rate law of an E1 reaction?

A

R = k[substrate] (unimolecular) (The rate determing step is the loss of LG)

36
Q

__________ halides favor the E1 mechanism & primary are least favored because the 1st step in E1 is the loss of LG which forms a carbocation & primary carbocation are least stable)

A

Tertiary halides

37
Q

In an E1 reaction if an alochol is the leaving group then a ______________ is needed to protonate it

A

Strong acid

38
Q

In an E1 reaction the regiochemistry can’t be controlled by a base & the ______________ is usually produced

A

Zaitsev product

39
Q

E1 don’t need a anti-periplanar conformation to react & favors the _________ product when stereoisomers are the products

A

Trans

40
Q

What are the two core steps of an E1 reaction?

A
  1. Loss fo LG
  2. Proton transfer
41
Q

What are the only 2 additional steps an E1 reaction can have?

A
  1. Proton transfer before the 1st step (loss of LG)
  2. Carbocation rearrangment in between the two core steps
42
Q

A proton transfer is needed at the beginning of an E1 reaction if an _________ is the leaving group & is needed to be protonated

A

Alcohol

43
Q

A carbocation rearrangement is needed in the middle of an E1 reaction if the carbocation can be ____________

A

More stable

44
Q

An E2 reaction has ________ additional steps

A

Zero its only a concerted reaction where the proton transfer & loss of Lg occur aqt the same time

45
Q

Why doesn’t E2 reaction have any additional steps?

A

It can’t form a carbocation & it uses strong bases & an OH can’t be protonated with a strong base

46
Q

___________ & ___________ reactions are always in competiton where sometimes one mechanims donminates & forms one product & other times both dominate & form multiple products

A

Substitution & Elimination reaction

47
Q

How do you determine which product is major & minor?

A
  1. Determine the function of the reagent
  2. Analyze the substrate & determine the expected mechanisms
  3. Consider any relevant regiochemical & stereochemcial requirements
48
Q

A substitution reaction occurs when the reagent acts as a ___________ & an elimination reaction occurs when the reagent acts as a _________

A

Nucleophile, Base

49
Q

Nucleophilicity

A

A kinetic phemomeon & refers to the rate of the reaction (refers to the rate at which a nucleophile attack an electorphile)

50
Q

Basicity

A

A thermodynamic phenomeon & refers to the position of equilibrium

51
Q

Factors that contribute to nucleophilicity

A
  1. Charge on an atom
  2. Polaraziability (More important than charge)
52
Q

Polarziabaility is directly portportional to the _________

A

Atomic mass

53
Q

In a proton equilbium it will favor the _________

A

The weaker base

54
Q

Reagents that are only strong nucleophiles indicates what type of reaction?

A

Substitution reaction

55
Q

What are the reagents that are only strong nucleophiles?

A
  1. Cl- 5. RS-
  2. Br- 6. H2S
  3. I- 7. RSH
  4. HS-
56
Q

Reagents that act only as strong bases indicate what type of reaction?

A

Elimination reaction

57
Q

What are the reagents that function only as strong bases?

A
  1. H-
  2. DBN
  3. DBU
58
Q

Reagents that function as both strong nucleophile & strong bases indicates what type of reaction?

A

SN2 & E2

59
Q

What are the reagents that are both strong bases & nucleophiles?

A
  1. HO-
  2. MeO-
  3. EtO
  4. RO-
60
Q

Reagents that are both weak nucleophile & bases indicate what type of reaction?

A

SN1 & E1

61
Q

What reagents function as both weak nucleophile & base?

A
  1. H2O
  2. MeOH
  3. EtOH
  4. ROH
62
Q

Protic solvents favor what type of reactions?

A

SN1 & E1

63
Q

Aprotic solvents favor what type of reaction?

A

SN2 & E2

64
Q

When a ______________ base is present (ex. t-ButOK) then the major product is the hofman product

A

Sterically Hindered (Bulky bases)

65
Q

______________ are a result of a sterically base being used

A

Less substituted

66
Q

__________________ refers to beta positions being identical or not (where if they are identical then one product will be formed & if they are non-identical then two or more products formed)

A

Regiochemistry

67
Q

When regiochemistry is not a factor (only have one beta position) then if there is two hydrogens on the beta position then _______________ comes into play where the trans conformation is the mjaor product

A

Stereoselectivity

68
Q

When regiochemistry & stereoselective isn’t a factor because only one beta position & there is only one hydrogen present then _______________ comes into play where have to make a newman projection so that the leaving group & beta hydrogen are anti-perilinear & then have to draw the newman projection that make them anti-perilinear

A

Stererospecific

Organic Chemistry (47 decks)

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