Alpha Carbon Chemistry: Enols & Enolates Flashcards
What is the mechanism for acid-catalyzed tautomerization?
- Proton Transfer
- Proton Transfer
The carbon next to the carbonyl group is an _____ carbon & it has _____ protons
Alpha
In the presence of a catalytic acid or base is present a ketone will exist on equilibrium with an ______
Enol
Enols are stable because why?
- They have a conjugated pie system which stabilizes it
- They can form hydrogen bonds
- An example of an enol is phenol
What is the mechanism for base-catalyzed tautomerization
- Proton Transfer
- Proton Transfer
The alpha position of enols _____ due to resonance structure.
Nucleophilic
When treated with a strong base the ketone alpha position is deprotonated to form an intermediate called __________
Enolate
An _____ is an ambident nucleophile because it can attack from two places the negative charge oxygen & the alpha carbon.
Enolate
When the negative charge oxygen attacks an electrophile is called an ________
O-attack
When the alpha carbon attacks an electrophile its called a __________
C-attack
Enolates are more useful than enols because why:
- Enolates posses full negative charge & more reactive than enols
- Enolates can be isolated
Only ______ protons of an aldehyde or ketone is acidic
Alpha protons
Aldehyde and ketones pka is usually what?
16-20
An alkoxide ion can be used as a base or a sodium hydride (H-) to convert aldehyde into an _______
Enolate
_______ is a base used to form enolates
LDA lithium diisopropylamide
Under acid-catalyzed conditions, ketones & aldehydes will undergo _________ at the alpha position
halogenation
What is the mechanism for acid-catalzyed halogenation of ketones?
- Proton transfer
- Proton transfer
- Nucleophilic attack
- Proton transfer
When an unsymmetrical ketone is used, bromination occurs primarily at the ________ position of the ketone
More substituted
The halogenated product can undergo elimination when treated with a _____
Base (any base can be used such as pyridine or Li2CO3 or t-BUTOK)
What is the hell-volhard-zelinsky reaction?
Alpha bromination of carboxylic acids
Alpha halogenation can occur easily with ketones & aldehydes however carboxylic acids, esters, or amides can’t do it easily & need a _____
Special reagent
Carboxylic acids can undergo alpha halogenation when treated with bromine in the presence of ______ which is
PBr3
Ketones can undergo alpha halogenation in _____
Basic Conditions
What is the mechanism for acid-catalyzed halogenation of ketones?
- Proton transfer
- Proton transfer
- Nucleophilic attack
- Proton Transfer
Under acid-catalyzed conditions, ketones & aldehydes will undergo halogenation at the _____ position
Alpha
In basic conditions, if there is more than one alpha proton available, the reaction will occur ____
Twice
When a methyl ketone is treated with excess base & excess halogen a _______ is formed (halofrom reaction)
carboxylic acid
When a methyl ketone is treated with __________ a haloform reaction occurs where it form a carboxylic acid
NaOH, Br2/ H3O+
Haloform reaction is most efficient when the other side of the ketone has _________
Has no alpha protons
When an aldehyde is treated with sodium hydroxide a _________ reaction occurs
Aldol addition reaction
The product of an aldol addition reaction is always a _________ aldehyde or ketone
Beta-hydroxy
What is the mechanism for an aldol addition reaction?
- Proton transfer
- Nucleophilic attack
- Proton transfer
For most simple aldehydes equilibrium favors the ________
Aldol product
For most Ketones the _______ is the favored product in equilibrium in an aldol reaction
Ketone
Retro aldol reaction
Is the reverse process of an aldol addition reaction so an aldol reaction converts back to an aldehyde or ketone
When treated in acidic or basic conditions, the product of an aldol addition reaction will undergo elimination to produce ___________
Unsaturation between the alpha & beta position (double bond between alpha and beta position)
Aldol condensation
When aldol addition & dehydration occur at the same time (water is lost)
The product of an aldol condensation is an _____________
alpha, beta-unsaturated aldehyde or ketone
What is the mechanism for an aldol condensation reaction?
- Proton transfer
- Nucleophilic attack
- Proton transfer
- Proton transfer
- Loss of LG
When two stereoisomeric pie bonds are formed the product with ________ is the major product
Fewer steric interaction
_______________ are aldol reactions that cab occur between different reactants
Crossed or mixed aldol reactions
If one aldehyde lack an _______ & has an unhindered carbonyl group then a cross-reaction can be used
Alpha proton
Cross aldol reaction can also be formed with ___________
Benzaldehyde
Aldol reaction using aromatic aldehydes generally produce ______________
Condensation reactions
Cross-aldol reaction can also be performed using _______ as a base
LDA
Compounds that have __________ can undergo intramolecular aldol reaction
two carbonyl groups
Intramolecular aldol reaction show preference for formation of ___________ member rings
5 & 6
Claisen condensation
Is a reaction where esters also exhibit reversible condensation reactions
In a clasien condensation reaction with ester use a base that has ___________
The sam eester group
What is the mechanism for claisen condensation reactions?
- Proton transfer
- Nucleophilic attack
- Loss of LG
- Proton Transfer
The product of a Claisen condensation reaction is a __________
Beta-keto ester
