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intermediate organic chemistry > Ch 22 > Flashcards

Ch 22 Flashcards

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1
Q

What is an enolate ion?

A

the conjugate base anion of a carbonyl compound formed when an alpha hydrogen is removed

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2
Q

Enolate ions can act as (electrophiles/nucleophiles)

A

nucleophiles, because they are anions.

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3
Q

What is an enol?

A

any compound when a hydroxide group is on one of the carbons in a double bond. (vinylic alcohol)

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4
Q

The enol form and original carbonyl compound are considered ______ ______.

A

constitutional isomers.

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5
Q

What is an alpha,beta unsaturated carbonyl compound?

A

Where there exists a double bond on the carbonyl compound connecting the alpha and beta carbon.

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6
Q

The higher the pKa, the (more/less) acidic.

A

The higher the pKa, the less acidic

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7
Q

Give 3 reasons for the acidity of alpha hydrogens

A

1) resonance stability and electron delocalization in the enolate ion
2) negative charge added to oxygen, an electronegative atom.
3) The polar dipole of the carbonyl can stabilize the carboxylate anion.

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8
Q

Aldehydes and Ketones are (more/less) acidic than esters. And by approx how many pKa units?

A

Aldehydes and Ketones are about 7 pKa units more acidic than esters.

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9
Q

Why are esters less acidic than Aldehydes and Ketones?

A

Esters do not have resonance when they are ionized, so it is more stable for them not to deprotonate.

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10
Q

Nitrogen analogs of enolate ions

A

amides!

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11
Q

Oxygen analogs of enolate ions

A

carboxylic acids!

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12
Q

What is the rank of acidity of amides, aldehydes/ketones, and carboxylic acids?

A

Carboxylic acids>amides>(aldehydes/ketones)

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13
Q

Enolate Ions can react with bronsted ____s.

A

bronsted acids

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14
Q

Two consequences of enolate ion formation and protonation

A

1) replacement of H with D

2) racemization of chiral aldehydes and ketones

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15
Q

Why are chiral aldehydes and ketones racemized?

A

the enolate ion is achiral and protonation from the bronsted acid can occur on either face.

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16
Q

Enolate ions are also Lewis ___.

A

Lewis bases, and therefore nucleophiles.

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17
Q

Enolate ions as nucleophiles often react with___(3)___

A

carbonyl carbons, alkyl halides, and sulfonate esters.

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18
Q

What is a tautomer?

A

Constitutional isomers that undergo such rapid interconversions that you cannot separate them.

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19
Q

How do tautomers relate to this chemistry?

A

A carbonyl compound and its enol are considered tautomers.

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20
Q

Which are more stable: Enols or the carboxylic acid?

A

The carboxylic acid

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21
Q

Why are carboxylic acids more stable than their enol counterparts?

A

The C=O bond is stronger in a carboxylic acid than the C=C bond. Also carbonyl oxygen provides some stabilization resonance.

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22
Q

What is an instance where the enol is more stable than it’s carboxylic counterpart?

A

In aromatic rings, the enol (phenol) is more stable than the keto isomer because the keto breaks aromaticity.

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23
Q

What is another example of a stable enol, and why?

A

Beta dicarbonyl compounds in their enol form have increased hydrogen bonding.

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24
Q

Base catalyzed enolization: involves the intermediacy of ____

A

an enolate ion.

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25
Q

Base catalyzed enolization: the ____ is the conjugate base of both the carbonyl compound and the enol.

A

enolate ion

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26
Q

Acid catalyzed enolization: An enol and its carbonyl isomer have the same ____

A

conjugate acid.

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27
Q

Acidity of Carbonyls: Rank allylic, amide, amine, ketone, aldehyde, ester, carboxylic acid

A

Most acidic= carboxylic acid>aldehyde>amide>ketone>ester>amine

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28
Q

Alpha Acidic Halogenation: 2 steps, and rates

A

First step: rate limiting formation of enol

Second step: fast halogenation step

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29
Q

Alpha Acidic Halogenation: Typically converts __ alpha hydrogens to halogens.

A

one

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30
Q

Base catalyzed Halogenation: Also called ____

A

The Haloform reaction

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31
Q

Base catalyzed Halogenation: typically replaces ____ alpha hydrogens with halogens

A

all

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32
Q

Base catalyzed Halogenation: The trihalomethane product is unstable and reacts with ____ and ____ to form a ____ and a ____.

A

OH and H3O+ to form a haloform and a carboxylic acid.

33
Q

Hell-Volhard-Zelinsky Reaction Part I

A

Carboxylic acid + Br2 –red phosphorous or PBr3–> replaces an alpha hydrogen with Br.

34
Q

Iodoform reaction

A

Alcohol –I2, base—> carbonyl

35
Q

Hell Volhard Zelinsky Reaction Part II

A

acid bromide enol form adds another Br (from Br2) to become an alpha bromo acid bromide.

36
Q

Hell Volhard Zelinsky Reaction Part III

A

in presence of small amount of PBr3, the alpha bromo acid bromide reacts with more carboxylic acid to form an alpha bromo acid.

37
Q

Hell Volhard Zelinsky Reaction Overall ( 2 separate condition paths)

A

1) catalytic amount of PBr3: provides alpha bromo acid

2) full equivalent of PBr3: provides an alpha bromo acid bromide

38
Q

Alpha bromo acid bromide + alcohol=

A

alpha bromo ester.

39
Q

Alpha halo carbonyl compounds with a good nucleophile (but weak base) provides a

A

alpha substituted carbonyl compound

40
Q

Alpha halo carbonyl compounds undergo (SN2/SN1)

A

SN2, cannot undergo SN1

41
Q

Why is SN1 not favored by carbonyl compounds?

A

The positive charge on the alpha carbon is destabilized ty the partial positive charge on the carbonyl carbon.

42
Q

General Base catalyzed Aldol Reaction (aldol addition)

A

2 equivalents of aldehyde –(NaOH,H2O)–> aldol

43
Q

What is an aldol?

A

A molecule with part alcohol, part aldehyde

44
Q

General Base catalyzed Aldol Reaction Mechanism(3)

A

1) [nucleophile(enol form)] + aldehyde
2) Protonation
3) Addition product

45
Q

Equilibrium for aldol addition is more favorable for (aldehydes/ketones)

A

more favorable for aldehydes than ketones

46
Q

Aldol Condensation Rxn

A

an aldol addition product can undergo dehydration to afford an alpha, beta unsaturated aldehyde.

47
Q

What favors an Aldol Condensation Step?

A

heat or excess base

48
Q

What occurs during the condensation step (mechanism)

A

Base attacks an alpha hydrogen, which creates a double bond, as the OH leaves.

49
Q

General Acid catalyzed Aldol Condensation

A

2 equivalents of aldehyde with the addition of acid provide an alpha, beta unsaturated carbonyl compound. THE ADDITION PRODUCT CANNOT BE ISOLATED.

50
Q

What are crossed aldol reactions?

A

Different carbonyl compounds coming together in an aldol reaction.

51
Q

Claisen-Schmidt Condensation

A

A ketone with alpha hydrogens condenses via –(NaOH)–> with an aldehyde with no alpha hydrogens, for example, benzaldehyde.

52
Q

Intramolecular Aldol Condensation

A

can occur when more than one aldehyde or ketone group exists, for example can create 6 membered rings

53
Q

Claisen Condensation

A

Base promoted condensation of two ester molecules to give a B keto ester

54
Q

What is a B keto ester?

A

It is a ketone group B to an ester group.

55
Q

Dieckmann condensation

A

an intramolecular Claisen condensation

56
Q

Claisen Condensation: very similar to

A

saponification

57
Q

Crossed Claisen Condensation

A

Combination of two different esters

58
Q

Useful Crossed Claisen Condensations:

A

When one ester is particularly reactive, or has no alpha hydrogens.

59
Q

Example of a useful crossed claisen condensation, and why:

A

ethyl formate: has no alpha hydrogens, and enhanced carbonyl reactivity ( easily interacts with nucleophiles.

60
Q

Another control of Crossed Claisens

A

using one reagent in excess causes one to react preferentially.

61
Q

Ketones and Esters (Claisen Condensation)

A

Ketone is more acidic and therefore forms the enolate. Ester cannot react with itself. Forms a B diketone.

62
Q

What is a B diketone?

A

ketone on the beta position. Looks like a dicarbonyl.

63
Q

Overall, Claisen condensations can be used in synthesis to create:

A

B dicarbonyl compounds, B keto esters, B diketones.

64
Q

Retrosynthesis: Dicarbonyls with a carbon in between.

A

Cut the bond between central carbon and carbonyl carbon in both possible places, and place an HOEt there, putting the EtO on the piece with the carbonyl.

65
Q

Aldol With LAH

A

Turns the carbonyl into an alcohol too.

66
Q

Aldol with PCC

A

Turns the alcohol into a carbonyl too.

67
Q

Alpha Beta unsaturated carbonyl compound with LAH

A

Turns the carbonyl into an alcohol.

68
Q

Alpha Beta unsaturated carbonyl compound with H2/Pd

A

Removes the double bond

69
Q

Alkylation of Ester Enolate Ions: Basic concept (general)

A

enolate ions can also acts as nucleophiles in SN2 Reactions

70
Q

Malonic Ester Synthesis ( 4 steps)

A

Ionization, alkylation, saponification, decarboxylation

71
Q

Direct Alkylation of Enolate Ions from Monoesters: Basic concept (general)

A

Alpha hydrogen replaced with alkyl component by e.g LDA in THF

72
Q

What is LDA?

A

Lithium Diisopropyl Amide (a very strong non nucleophilic base that can esters to form their conjugate base ions)

73
Q

Acetoacetic ester synthesis ( 3 steps)

A

saponification, protonation, decarboxylation

74
Q

Conjugate Addition Reactions (General)

A

Places H-A across a double bond via enolate ion intermediate.

75
Q

1,4 addn rxns (thermo/kinetic)

A

thermodynamic, adds the nucleophile to the 4 position on alkene

76
Q

1,2 addn rxns (thermo/kinetic)

A

kinetic, adds the nucleophile to the carbonyl carbon.

77
Q

Cu (cuprates) 1,4 addn, or 1,2?

A

1,4 thermodynamic product, soft

78
Q

Li/Grignard 1,4 addn or 1,2?

A

1,2 kinetic, adds to the carbonyl carbon

79
Q

Michael Addn

A

Diester + NaOEt creates enolate that adds to the 1,4 position of an alkene.

intermediate organic chemistry (8 decks)

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