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OChem 1 > Quiz 5 > Flashcards

Quiz 5 Flashcards

1
Q

Nucleophilicty

A

the strenght of a nucleophile, how fast does the nucleophile attack an electrophile

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2
Q

Name the four factors that affect nucleophilicty

A
  1. size
  2. charge
  3. solvent
  4. polarizibility
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3
Q

How does size affect nucleophilicity?

A

a smaller atom is favored

excpet in polar protic solvents

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4
Q

How does charge affect nucleophilicty?

A

a nucleophile with a charge will be stronger

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5
Q

How does polarizibility affect nucleophilicty?

A

it determines how well the nucleophile can unevelnly dsitrubite a charge

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6
Q

How does a solvent affect nucleophilicity?

A

it can slow down or speed up the rxn by creating a solvent shell around the nucleophile or not

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7
Q

Polar protic solvent

A

has hydrogen bonding, bad for SN2 rxns bc it creates a solvent shell

but favored for SN1

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8
Q

Polar aprotic solvent

A

does not have hydrogen bonding, good for SN2 reactions because it doesnt create a solvent shell

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9
Q

Inversion of configuration

R–S or S–R

A

when a reactant starts with one configuration and the products end with the other configuration

happens bc back side attack

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10
Q

Backside attack

A

nucleophile attatches on opposite side of leaving grp

affects how you draw the mechanistic arrow

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11
Q

Beta elimination

E2 rxn

A

when an alykl halide is treated with a strong base and a pi bond is formed
- proton transfer + loss of a leaving group

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12
Q

What are the products of a beta elimination?

A

con A of base + solo halogen + Alkene

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13
Q

Is an E2 reaction bimolecular and concerted or bimolecular and stepwise?

A

An E2 reaction is bimolecular and concerted
- relying on the substrated and the base for its rate

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14
Q

There must be a — on the beta carbons or an — reaction cant happen

A

Hydrogen, beta elimination/E2

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15
Q

In an E2 rxn the alkene must form between the — and —

A

alpha C and Beta C

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16
Q

How can a base affect the E2 rxn?

A

It can speed it up or slow it down depending on its strenght
- the stronger the base is the faster it can deprotonate the molecule

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17
Q

What is the key difference between an E2 and SN2 rxn?

A

You want a more sterically hindered product, because they are more stable and a sterically hindered substrate so the H are accesible for the base

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18
Q

True or false?

A cis alkene is more stable than a trans alkene bc there is resonance

A

false, a trans alkene reduces interaction between substituents

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19
Q

put 1,2,3,and 4 substitued alkenes in order of increasing stability

A

monosub<disub<trisub<tetrasubstitued

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20
Q

Regioselectivity

A

when there is a major/minor product produced and one is favored over the other, the region where the reaction takes place

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21
Q

True or false?

The more highly substitued the base is the more likely the Zatisev product will be favored

A

False, the more subsituted the base is the more likely the hoffman product will be favored (the less substitued alkene)

22
Q

Zatisev product

A

more substitued alkene

23
Q

Hoffman product

A

less substitued alkene

24
Q

Stereospecific

A

One beta H, produces one stereoisomer (most stable one)

SN2 and E2 under right conditions

25
Q

Stereoselective

A

2+ beta H, will produce a major and minor product in unequal amounts

E2 rxns

26
Q

Anti coplanar/anti periplanar

A

staggard conformation where Beta H and leaving group on opposite planes of each other

lower E makes this the favorable conformation

27
Q

Periplanar/syn-planar

A

eclipsed conformation where Beta H and leaving group are on the same direction

very high E transistion state, not favorable for a E2 reaction

28
Q

If a molecule is syn-planar/periplanar what should you do?

A

rotate the bonds so the molecules are anti planar

29
Q

If an E2 reaction is happening with a substitued cyclohexane what has to be true of the leaving group and beta H?

A
  1. leaving group has to be axial
  2. the leaving group and beta H have to be anti coplanar/antiperi planar to each other (just like in non cycloalkanes)
30
Q

How do unimolecular reactions differ from the biomolecular substituion and elimination reactions?

A
  1. these reactions occur stepwise: at least two transition states and one intermediate
  2. rate depends only on the substrate and not the solvent
  3. Both SN1 and E1 prefer a hindered substrate
31
Q

what is the first step of a unimolecular substitution and elimination reaction and what determines what the next mechanistic step is?

A

first step: Loss of a leaving group
the solvent determines if a nucleophilic attack or a proton transfer will follow

32
Q

True or false?

A unimolecular reaction will produce both SN1 and E1 products

A

True! one will just be featured more depending on the solvent

33
Q

Adding — to a unimolecular reaction will increase the likelihood of a Elimation reaction?

A

Heat will increase the probability of an elimination reaction

34
Q

Unimolecular reaction favor a — substrate

A

hindered

35
Q

True or false?

a primary vinylic and allylic carbocation can never form

A

false, an allylic primary carbocation can form because of resonance. aryl and vinyllic cannot form

36
Q

What kind of solvent is favored for a unimolecular reaction?

A

Polar protic, it can stabilize the partial charges (carbocations) that form during the reaction

37
Q

If your product has a charge at the end of the reaction what should be done?

A

a proton transfer, a charged product is higly unlikely because it would be unstable

38
Q

True or false?

Just like SN2 an SN1 reaction will always produce inversion of configuration

A

false, an SN1 reaction will produce both retention and inversion products

39
Q

In unimolecular reactions will the hoffman or zaitsev product be favored?

A

Zaitsev, more substiuted and more stable

the E isomer will also likely be favored

40
Q

What are the four catagories of reagant?

A
  1. Strong nucleophile, acts only as a nucleophile
  2. strong base, acts only as a base
  3. strong nucleophile, strong base
  4. weak nucleophile, weak base
41
Q

What kind of reaction does a strong nucleophile that acts only as a nucleophile promote?

A

this will promote a SN2 reaction

42
Q

Examples of strong nucleophiles that act only as nucleophiles

A

solo halogens: I-, Br-, Cl-
HS-

43
Q

what kind of reaction does a strong base that only acts as a base promote?

A

likely will promote an E2 reaction

44
Q

example of strong bases that act only as bases

A

DBU, DBN, tert-butoxide, strong bulky bases

45
Q

What kind of reaction do strong nucleophile/strong base promote?

A

Bimolecular reactions

46
Q

examples of strong nucleophile/ strong base

A

charged O- or N-, MeO-, EtO-, -OH

47
Q

What kind of reactions will a weak nucleophile/ weak base promote?

A

unimolecular reactions

48
Q

examples of weak bases/ weak nucleophiles

A

neutral oxygens, Water, Alcohols
MeOH, Et,OH, H2O

49
Q

True or false?

A heavily subsiuted substrate will indicate any reaction that is not SN2

A

True, Sn2 is the only reaction that does not favor a hinderd substrate

50
Q

Will the zaitsev or hoffman product be favored in an E1 reaction?

A

In an E1 reaction zaitsev is always favored

OChem 1 (8 decks)

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