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CHEM 351 > Elementary Steps and Mechanisms > Flashcards

Elementary Steps and Mechanisms Flashcards

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1
Q

Which elementary step is pictured?

A

Nucleophilic Addition

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2
Q

Which carbocation is least stable?

methyl, 1º, 2º, 3º

A

methyl carbocation

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3
Q

Which carbocation is most stable?

methyl, 1º, 2º, 3º

A

3º carbocation

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4
Q

In an SN1 reaction is it stereospecific (only get R OR S not both) or will you get racemization (get both R AND S)?

A

An SN1 reaction will give you both R and S stereoisomers

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5
Q

Will adding heat favor substitution(SN1/SN2) or elimination(E1/E2)?

A

Adding heat will favor elimination pathways

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6
Q

In an E2 reaction do you get both E AND Z stereoisomers or do you only get one (E OR Z)?

*If you get both, which stereoisomer is favored?

*If you only get one, why?

A

You get one or the other (E or Z)

In an E2 reaction the leaving group and the H that are eliminated must be 180º away from eachother (anti)

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7
Q

Is ethanol a protic or aprotic solvent?

A

protic

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8
Q

Which elementary step is pictured?

A

Electrophile Addition

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9
Q

How do you classify a base as “weak”?

A

It must be weaker than -OH

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10
Q

Does a weak base promote E1 or E2?

A

weak bases promote E1

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11
Q

For an elementary step with a negative delta Gº will the transition state resemble reactants or products?

A

It will favor reactants

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12
Q

Is acetone a protic or aprotic solvent?

A

aprotic

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13
Q

Does nucleophile concentration effect the rate of SN1/E1 reactions?

A

No

SN1/E1 reactions ar eonly dependent on substrate concentration

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14
Q

Does a strong base promote E1 or E2?

A

Strong bases promote E2

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15
Q

Is DMF a protic or aprotic solvent?

A

aprotic

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16
Q

Which elementary step is pictured?

A

Proton Transfer

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17
Q

If your substrate is 3º (tertiary) - which reactions will it favor (or which will it not favor)?

(SN1/SN2/E1/E2)

A

it will not favor SN2

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18
Q

Do polar protic solvents favor SN1/E1 or SN2/E2?

A

polar protic solvents favor SN1 and E1

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19
Q

Which elementary step is pictured?

A

E2

Bimolecular Elimination

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20
Q

When will a reaction (SN1, SN2, E1, or E2) occur?

If the Carbon bonded to the leaving group is sp, sp2, or sp3 hybridized?

A

SN1, SN2, E1, or E2 can only occur if the carbon bonded to the leaving group is sp3 hybridized

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21
Q

What will the rate determining step correlate with on a reaction energy diagram?

A

It will correlate with the highest free energy point on the diagram

22
Q

If your substrate is methyl - which reactions will it favor?

(SN1/SN2/E1/E2)

A

methyl favors SN2

23
Q

What is a polar protic solvent?

A

A solvent that has the ability to be a hydrogen bond donor (i.e. can donate H’s)

24
Q

Is H2O a protic or aprotic solvent?

A

protic

25
Q

Which elementary step is pictured?

A

Coordination

26
Q

What is a polar aprotic solvent?

A

A solvent that can only accept H’s - it can not donate them

27
Q

Is DMSO a protic or aprotic solvent?

A

aprotic

28
Q

Does a weak nucleophile promote SN1 or SN2?

A

Weak nucleophiles promote SN1

29
Q

Does a strong nucleophile promote SN1 or SN2?

A

Strong nucleophiles promote SN2

30
Q

How do you classify a base as “strong”?

A

It must be at least as strong as -OH

31
Q

In an E1 reaction do you get both E AND Z stereoisomers or do you only get one (E OR Z)?

*If you get both, which stereoisomer is favored?

*If you only get one, why?

A

You get both E and Z

*the most stable isomer is preferred

32
Q

Which elementary step is pictured?

A

Heterolysis

33
Q

If your substrate is 2º (secondary) - which reactions will it favor?

(SN1/SN2/E1/E2)

A

it will favor all

(SN1/SN2/E1/E2)

34
Q

Does nucleophile concentration effect the rate of SN2/E2 reactions?

A

Yes

SN2/E2 reaction rates are dependent on both nucleophile and substrate concentrations

35
Q

For an elementary step with a positive delta Gº will the transition state resemble reactants or products?

A

It will favor products

36
Q

Is formamide a protic or aprotic solvent?

A

protic

37
Q

Which elementary step is pictured?

A

Nucleophile Elimination

38
Q

In an SN2 reaction is it stereospecific (only get R OR S not both) or will you get racemization (get both R AND S)?

A

SN2 reactions are stereospecific- you will get the opposite steroisomer

39
Q

If your substrate is 1º (primary) - which reactions will it favor?

(SN1/SN2/E1/E2)

A

1º substrates favor SN2 and E2

(benzyl and allyl carbons will favor SN1 and E1)

40
Q

Which carbocation will have the slowest reaction rate?

methyl, 1º, 2º, 3º

A

methyl carbocation

41
Q

Which elementary step is pictured?

A

E1

42
Q

Which elementary step is pictured?

A

Carbocation rearrangements

43
Q

What is the rate determining step for an SN1 reaction?

A

heterolysis

44
Q

Which elementary step is pictured?

A

Electrophile Elimination

45
Q

Which carbocation will have the fastest reaction rate?

methyl, 1º, 2º, 3º

A

3º carbocation

46
Q

Which elementary step is pictured?

A

SN1

47
Q

Do polar aprotic solvents favor SN1/E1 or SN2/E2

A

polar aprotic solvents favor SN2/E2

48
Q

Which elementary step is pictured?

A

SN2

Bimolecular Substitution

49
Q

Is acetonitrile a protic or aprotic solvent?

A

aprotic

50
Q

elimination with a (regular) base will prefer the less or more substituted alkene?

A

elimination usually takes place to favor the most highly subsituted alkene

51
Q

elimination with a big, bulky base will prefer the less or more substituted alkene?

A

it will prefer the less highly substitued alkene

52
Q
A

CHEM 351 (14 decks)

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