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ochem2 > enols and enolate > Flashcards

enols and enolate Flashcards

1
Q

Through what process are enols formed?

A

Keto forms of aldehydes and ketones are tautomerized

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2
Q

What is the difference of tautomers and constitutional isomers?

A

Tautomers differ in H bonds and double bond

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3
Q

How many steps are present in acid catalyzed enolization?

A

2 steps + 1 resonance (PRDD)
Protonate, Resonance, Detach/Double bond

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4
Q

How many steps are present in base enolization?

A

2 steps + 1 resonance (DRP)
Detach,
Resonance,
Protonate

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5
Q

What hydrogens are acidic in ketones?

A

Alpha hydrogens are more acidic since when they are removed they are able to form resonance structures. Beta and gamma hydrogens do not allow for resonance

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6
Q

Why are beta diketones more acidic than regular ketones?

A

They have three sets of alpha hydrogens which can be removed and have three resonance structures

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7
Q

What happens if there is a stereocenter in base reactions?

A

Carbon can attack from either side

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8
Q

What is the importance of the aldol condensation reaction?

A

You can use it to incorporate deuterium

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9
Q

What are the reaction conditions of aldol condensation? What intermediate is formed?

A

Reactant: 2 aldehyde or ketone
Conditions NaOH| H2O then heat
Product: alpha, beta-unsaturated aldehyde
*beta hydroxyaldehyde intermediate

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10
Q

How many steps are in the aldol condensation mechanism?

A

5 steps + 1 resonance
Detach,
Resonance,
Protonate,
Detach/Double Bond
Electron movement

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11
Q

How is equilibrium influenced in the aldol condensation reaction?

A

Aldehyde reaction will favor beta hydroxyaldehyde
Ketone reaction will favor ketone

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12
Q

What happens if instead of 2 equivalents of one aldehyde or ketone you have one of each or two different ones?

A

You get a mixture which is not useful

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13
Q

How do you avoid a mixture of beta hydroxyaldehyde products?

A

Only one reactant can form an enolate and one reactant is more electrophilic

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14
Q

What are enols?

A

Compounds with a double bond and hydroxyl group

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15
Q

What are the relative pka values of alpha hydrogens in aldehyde, ketone, beta- diketone, ester, beta-ketoesters?

A

Aldehyde 16
Ketone 20
Beta-diketone 9
Ester 4
Beta-ketoesters 11-13

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16
Q

How many enolate ion resonance structures do esters and beta-ketoesters have?

A

Esters have two
Beta-keto esters have three

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17
Q

How do the oxygens of an ester contribute to the stability of the carbon in the carbonyl bond? Is it more stable than aldehyde or ketones?

A

Double bond O is a EWG via resonance
C-O is EDG and shares electron density
Yes more stable than aldehydes or ketones

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18
Q

Where does equilibrium lie in ester enolate formation?

A

To form the enolate

19
Q

What is an ester enolate?

A

Compounds with C=C and OR and OH

20
Q

What are the reaction conditions of claisen condensation? What is a special condition?

A

Reactant: ester with a beta carbon having 2 hydrogens
Conditions: 1) NaOR, ROH 2) H3O+
Product: beta-keto ester
OR of ester, and conditions must be the SAME

21
Q

What is the importance of the number of beta hydrogens and pka in claisen condensation?

A

Acidity drives the reaction to completion and with one beta hydrogen the equilibrium lies to reactant

22
Q

Which carbon is the nucleophile in a claisen condensation?

A

Alpha carbon

23
Q

How many steps are in the claisen condensation mechanism?

A

5 steps

24
Q

What are the reaction conditions for diekmann cyclization?

A

Reactant: di ester
Conditions: 1) NaOR, ROH 2) H3O+
Product: 5 or 6 C ring with C=O in ring and one outside

25
Q

What rules must be considered for a mixed claisen condensation?

A

One compound must be enolizable and the other must be more nucleophilic/basic

26
Q

What are the reaction conditions for acetoacetic ester synthesis?

A

Reactant: ester
Conditions: 1)NaOR, ROH 2) H3O+ then R-X (sn2)
Product: ketone

27
Q

What are the reaction conditions for malonic ester synthesis?

A

Reactant: Malonic ester (beta di ester)
Conditions: 1) NaOR, ROH 2) H3O+, RX, 1) NaOH, H2O, heat 2) H3O+, heat
Product: carboxylic acid

28
Q

What are the reaction conditions of alkylation of enolates?

A

Reactants: ketone with alpha hydrogens
Conditions: 1) LDA, ether 2) R-X (sn2)
Product: ketone with R group at alpha carbon
*enolate intermediate

29
Q

Why do you have to use LDA and not hydroxide or alkoxide in the alkylation of enolates?

A

Their relative pka values and leads the equilibrium to lie towards the ketone reactant and not the enolate ion product

30
Q

What is the benefit of using LDA?

A

Neutral amine product is more acidic than ketone product and leads reaction to the product and is irreversible. It is a good base to take of alpha hydrogen and not attack the carbon of the C=O (bad nucleophile)

31
Q

What are alpha beta unsaturated carbonyls? Do they have resonance?

A

Conjugated systems that have a double bond at the alpha and beta carbon and are able to form 2 resonance structures

32
Q

Where do weak bases attack alpha beta unsaturated carbonyls? What does this result in?

A

Attack at the beta carbon resulting in 1,4 addition

33
Q

What are the 5 weak bases in the 1,4 addition?

A

-CN, -SR, RNH2, R2CuLi, enolate ion of beta dicarbonyl

34
Q

Where do strong bases attach alpha beta unsaturated carbonyls? What kind of addition do they result in?

A

Alpha carbon. Result in 1,2 addition

35
Q

What are the 3 strong bases used in alpha beta unsaturated carbonyl attack?

A

RMgX, RLi, LiAlH4

36
Q

What kind of controls are the different types of addition?

A

Thermodynamic control- 1,4 addition
Kinetic control- 1,2 addition

37
Q

What does 1,2 addition of alpha beta unsaturated carbonyls form?

A

Alcohol

38
Q

What does 1,4 addition of alpha beta unsaturated carbonyls form?

A

Enolate intermediate to ketone

39
Q

What are the reaction conditions of Michael addition?

A

Reactant: alpha beta diketones
Conditions: NaOR, ROH
Product: enolate ion

40
Q

What are the reaction conditions of halogenation of enols?

A

Reactant: ketone
Conditions: X2, solvent
Product: ketone with halogen on alpha carbon

41
Q

What are the reaction conditions of haloform formation?

A

Reactants: ketone
Conditions: NaOH | X2 might be seen as 1) X2, NaOH, H2O 2) H3O+
Product: carboxylate ion and haloform (HCX3)

42
Q

Is the keto or enol form preferred in equilibrium?

A

Keto form

43
Q

List the following from most to least acidic: ester, ketone, aldehyde, beta- keto ester, beta- di ketone

A

(most) beta- diketone, aldehyde, beta- keto ester, ketone, ester (least)

ochem2 (13 decks)

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