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Chem 210 > Exam 3 > Flashcards

Exam 3 Flashcards

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1
Q

What reaction type do strong nucleophiles favor?

A

SN2 reactions

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2
Q

What reaction type do weak nucleophiles favor?

A

SN1 reactions

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3
Q

How does charge correlate to nucleophile strength?

A

a more negative charge = stronger nucleophile

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4
Q

What is the trend of nucleophile strength on the periodic table?

A

increases towards carbon

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5
Q

What reaction type do strong bases favor?

A

E2

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6
Q

What reaction type do weak bases favor?

A

E1

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7
Q

How to determine a weak base?

A

it is the conjugate base of a strong acid; add an H+ proton and determine acid strength

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8
Q

What reaction types does a high concentration of attacking species favor?

A

SN2 and E2 (assume high conc. unless specified)

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9
Q

What reaction types does a diluted (dil.) concentration of attacking species favor?

A

E1 and SN1

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10
Q

What kind of base or acid do leaving groups tend to be?

A

weaker bases

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11
Q

What is TsO-?

A

one of the best leaving groups

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12
Q

What is MsO-?

A

one of the best leaving groups

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13
Q

What is TfO-?

A

one of the best leaving groups

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14
Q

What is HSO4-?

A

one of the best leaving groups

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15
Q

What reaction types do good leaving groups favor?

A

all of them

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16
Q

What reaction types do poor leaving groups favor?

A

SN2 and E2 reactions

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17
Q

What reaction types does heat (∆) favor?

A

elimination (E1 and E2)

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18
Q

What hybridization must a carbon have for a SN1, SN2, E1, or E2 reactions to occur?

A

sp3

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19
Q

Why does sp3 hybridized carbon allow substitution and elimination reactions to occur?

A

because it has the weakest bond strength and electronegativity making it easy for the LG to leave

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20
Q

What reaction types does a primary carbon bonded to the leaving group favor?

A

SN2 and E2

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21
Q

What reaction types does a secondary carbon bonded to the leaving group favor?

A

all of them

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22
Q

What reaction type does a tertiary carbon bonded to the leaving group prevent?

A

SN2

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23
Q

What is the only reaction type a methyl carbon bonded to the leaving group allows?

A

SN2

24
Q

What type of solvent is DmSO?

A

Aprotic

25
Q

What type of solvent is DMF?

A

Aprotic

26
Q

What type of solvent is THF?

A

Aprotic

27
Q

What type of solvent is acetone?

A

Aprotic

28
Q

What reaction types do aprotic solvents favor?

A

SN2 and E2 reactions

29
Q

Why do aprotic solvents favor E2 and SN2 reactions?

A

because they solvate weakly so they don’t block the nucleophile from attacking the molecule

30
Q

What type of solvents have N-H or O-H bonds?

A

Protic solvents

31
Q

Why do protic solvents favor SN1 and E1 reactions?

A

because they strongly solvate the nucleophile, making it less reactive, and strongly solvate the LG making it more reaction

32
Q

Which regiosomer do elimination reactions favor according to Zaitzev’s rule?

A

the major regiosomer is the one with the less substituted alkene (pg. 11 of Carra notes)

33
Q

What is a regioisomer?

A

isomers with the same functional groups attached at different positions of the molecular backbone

34
Q

Do low concentration reaction favor intramolecular interactions or intermolecular interactions?

A

intramolecular (within one molecule)

35
Q

Do high concentration reaction favor intramolecular interactions or intermolecular interactions?

A

intermolecular (between multiple molecules)

36
Q

What are important rules/limitations of using PBr3 and PCl3 to convert alcohol into alkyl halides?

A

the carbon must be sp2 hybridized
it cannot be a tertiary carbon
it is a stereospecific reaction

37
Q

Which type of molecule (1st step) facilitates the attachment of an alkyl to the least substituted alpha carbon during alkylation of an alpha carbon?

A

Strong bulky bases

38
Q

What kind of atom must be attached to an alkyl (2nd step) for alkylation of an alpha carbon to occur?

A

a halogen (Br)

39
Q

Why do strong bulky bases cause alkylation on the least substituted alpha carbon of a molecule?

A

the de-protonation of less the sterically hindered H is irreversible

40
Q

Which type of molecule (1st step) facilitates the attachment of an alkyl to the most substituted alpha carbon during alkylation of an alpha carbon?

A

bulky bases weaker than LDA

41
Q

Why do bulky bases weaker than LDA alkylation on the most substituted alpha carbon of the molecule?

A

because the deprotonation of the less sterically hindered H is reversible, so the more stable enolate is able to form

42
Q

What is a enolate?

A

a deprotonated (has a lone pair and (-) charge) oxyen-carbon double bond in a molecule

43
Q

What is a therodynamic enolate?

A

a more stable enolate

44
Q

What enolate does room temp favor?

A

theromdynamic enolate

45
Q

What is the first step of halogenation of an alpha carbon?

A

to deprotonate the alpha carbon using a base from the solvent

46
Q

What is the second step of halogenation of an alpha carbon?

A

the lone pair of the enolate attacks the partial positive of the halogen pair

47
Q

How does halogenation of an alpha carbon affect stereochemistry?

A

a mixture of 2 stereoisomers is created because the during the sp2 hybridized phase of the enolate, the molecule becomes planar

48
Q

When does polyhalogenation occur?

A

when more than one H exists on the alpha carbon for the halogens to replace

49
Q

Why would polyhalogenation not occur even if more than one H is on the alpha carbon?

A

acidic conditions

49
Q

What product forms when a akylhalide (R-X) is reacted with a alkoxide ((-)OR’)

A

R - O - R’ (an ether)

50
Q

What is this reaction called: R-X → R - O - R’
(→ = (-)OR’)

A

Williamson Ether Synthesis

51
Q

What type of reaction occurs during Williamson Ether Synthesis?

A

SN2

52
Q

What step must first occur before an alcohol can undergo William Ether Synthesis?

A

a base must deprotonate it

53
Q

What is limitation/rule of William Ether Synthesis?

A

it cannot occur at tertiary alkyl halides 3* carbons can not perform SN2 reactions

54
Q

Does an intermolecular/intramoleculer reaction occur if a halide ion and alkoxide are on the same molecule?

A

an intramolecular William Ether Synthesis

55
Q

What is an alpha carbon?

A

a carbon that is one away from a Ketone or Aldehyde (carbon-oxygen double bond)

Chem 210 (2 decks)

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