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Organic Chem Quiz 5: Enols and Enolates (Aldol reaction gives beta…
Organic Chem Quiz 5: Enols and Enolates
Haloform reaction
transformation of a methyl ketone to a carboxylic acid
Key Idea: Using a Halogen (Cl-,Br-)
Conditions: Basic
Mechanism
Deprotonate alpha carbon form enolate ion
Note: C is the nuc site
Alpha carbon attacks Halogen (Br)
Br- is hooking up with Na+
Repeat steps 1-2 two more times
After third bromination, OH- is the nuc and attacks the carbonyl carbon
The alpha carbon is a good leaving group and is pushed off
Then either the OH- or CBr3- deprotonates the OH still attached
Work up step, O is protonated
This is like alpha-bromination of an enol
Enolates in alkylation reactions with alkyl halids or alkyl tosylates
Adds R group to alpha carbon
Best R group primary methyl
Mechanism
Deprotonation of alpha carbon
Enolate nuc attacks alkyl halide
Note: SN2 reactions
Basic Conditions
Aldol reaction gives beta-hydroxycarbonyl
2 uses of reactants
1 is the nuc (enolate)
1 is the elec
Basic Conditions
NaOEt is very common to use
Base is the catalyst
Mechanism
Base deprotonates acid
Nuc enolate attacks the elec reactant
alpha beta new C-C bond forms
Protonates beta Oxygen by reforming the base
Reversible because enolate is stable leaving group
enolate is stable because of resonance structures
Mixed Aldol reaction
"mixed" - 2 different aldehydes or ketones are used
Dehydration/condensation of aldol products to get alpha,beta-unsaturated carbonyl products
Basic conditions OH leaves as Hydroxide
Mechanism
1.OEt attacks alpha H (deprotonation)
Electrons push onto alpha beta bond, then push OH off
Acidic conditions OH leaves as H2O
Mechanism
OH protonates by deprotonating H3O+
2.Pushes H2O off
H2O deprotonates alpha carbon
Not E2 elmination because it has an intermediate
Doing E1cb
1 intermediate, CB stands for conjugate base
Alpha beta double bond is preferred over beta gamma
Product could go on to do 1,4-addition to make an aldol condensation product
Claisen condensation: esters to make beta-keto esters
Differences in aldol reaction
2 C=O in product
H3O+ work up
Similar to aldol reaction
2 carbonyl families
1 becomes enolate nuc
Other is the elec
Basic conditions
Mechanism
OEt- deprotonates alpha carbon forming enolate