ALdehydes and Ketones: Enolates Flashcards
Alpha Carbon
adjacent to the carbonyl carbon
Alpha Hydrogens
hydrogens connected to the alpha carbon
acidity is augmented by resonance stability of the conjugate base, the extra electrons remaining from H being removed can resonate between: alpha C, carnonyl C, and carbonyl O
this causes increased stability of the enolate intermediate
Through _____ , oxygen pulls ______ out of the C-H bonds of alpha C-H bonds weakening them and making it easy to deprotonate the ______ of an aldehyde/ketone.
induction
electron density
carbonyl carbon
Alpha hydrogens of ketone tend to be slightly _____ acidic than those of aldehyde due to the electron donating properties of the ________ in a Ketone.
less
alkyl groups
Aldehydes are _____ reactive to nucleophiles than ketones because of the ______ from the _____.
The ____ make the ____ a high energy intermediate meaning the reaction is _______ to proceed.
more
steric hinderance
alkyl groups
alkyl groups
ketone
less likely
Due to the acidity of the ______, aldehydes exist in solution as a mixture of two isomers: the ____ and ____ form.
alpha hydrogen
keto
enol
Enol Form
presence of C-C double bond with an alcohol
occurs from the deprotonation of the alpha carbon by a strong base such as: OH, LDA, KH
Tautomers
isomers which differ in placement of a proton and the double bond
aka: keto form vs enol form
Equilibrium between the tauromers lies on the ____ side meaning more of the ____ isomer is in solution.
keto
keto
Enolization/Tautomerization
process of converting from the kero to the enol tautomer
Alpha Racemization
any aldehyde and ketone with a chiral alpha carbon will rapidly become a racemic mixture as the Keto and enol form interconvert
Michael Addition
carbanion attacks an alpha, beta unsaturated carbonyl compound (multiple bonds between the alpha and B carbons next to a carbonyl)
Given a ketone has two different alkyl groups, each may have a alpha hydrogen meaning _____ enolate forms can exist.
two
Kinetic Enolate
rapidly made but less stable
double bond to the less subsituted alpha Carbon
favored in rapid, irreversible, lower temperatures with a strong, sterically hindered base
Thermodynamic Enolate
slowly made but more slowly
double bond being formed with the more substituted alpha carbon
favored in reversible, high temperature slow reaction with weaker and smaller base
Enamines
tautomers of imines
hydrogen moves to Nitrogen and double bond moves between C-C
Imine
compound with a C-N double bond
the nitrogen may or may not be bonded to an alkyl or other substituent
Aldol Condensation
aldehyde/ketone acts both as electrophile (keto from) and nucleophile (enol form) and a C-C bond is formed
type od dehydration/condensation reaction
1) enolate is formed when reacting ketone with base
2) due to enolates negative charge on O, it acts as nucleophile and react with the carbonyl of another ketone
3) it attacks the carbonyl carbon and produces an Aldol
4) strong base/high temp creates dehydraton via E1 or E2 to form a double bond between alpha and B carbon
**useful if we only use one type of aldehyde or ketone
if multiple types are used, then there are a mixture of products…but can be avoided if one molecule has no alpha hydrogen (quaternaty alpha carbon)
Aldol
compound with both aldehyde and alcohol
Retro Aldol Reaction
reverse of aldol condensation by adding aq base and hear
helps break bonds between alpha and B carbons of a carbonyl
only possible if intermediate can be an enol
