Aldehydes and Ketones Flashcards
physical properties
- double bonded oxygen is more electron withdrawing
- dipole moments inc intermolecular attractions
- elevation in bp, but less than that of alcohols because no H-bonding
- act as electrophiles and thus are good targets for nu
- EWG properties explain this, partial positive on carbonyl carbon
- aldehydes more reaction to nu than ketones bc less steric hindrance and fewer e- donating alkyl groups
1° alcohol ~~PCC~~>
aldehyde, but any stronger oxidant aldehyde will turn to CA
2° alc ~~ (Na or K)2Cr2O7 or CrO3 or PCC~~>
ketone
after a nu attack and the electrons are kicked up to the oxygen in rxn w carbonyl…
- no good LG and the nu has covalently bonded to carbon, therefore no carbonyl repair
- tetrahedral intermediate
in the presence of water, both aldehydes and ketones form…
geminal diols
o in water is nu
basic conditions
aldehyde or ketone react w 1 eq alc
hemiacetal or hemiketal
anhydrous acid
aldehyde or ketone react w 2 eq alc
- SN1
- acetal or ketal
- used at protecting groups for carbonyl functionalities
- aqueous acid and heat easily converts them back
condensation rxn
- a small molecule is lost during the formation of a bond between two molecules
nitrogen and nitrogen-based functional groups act how when reacting with carbonyls
good nu
imine formation
- ammonia nu attacks carbonyl carbon, water is lost, imine is formed
- condensation reaction
- nu substitution
imines undergo tautomerization to form…
enamines
cyanohydrins
- HCN is common nu
- both triple bonds and an electroneg N atom, rendering it relatively acidic
- CN- attacks carbonyl carbon and O is protonated by H+
aldehyde reacts with what to become CA?
KMnO4, CrO3, Ag2O, H2O2
commons reduction agents
LiAlH4
NaBH4
why is it easier to deprotonate a-H (esp in basic conditions)
induction, oxygen pulls some e- density out of these C-H bonds weakening them
acidity of a-H augmented by resonance stabilization of the conjugate base
inc stability of enolate intermediate and EW oxygen helps with this carbanion stabilization
why are a-H of ketones less acidic than aldehyde
electron donating properties of the additional alkyl group on ketone
a 1,3-dicarbonyl…
- is particularly acidic
- 2 carbonyls delocalize the neg charge
- form enolate carbanions in Michael addition for the nucleophilic carbanion to readily react w electrophiles
1,3-dicarbonyl ~base~> ——— ~ketone~>______
- enolate and H—base
- the a of the a,B-unsat bicarbonyl attached to the B-carbon of the ketone
which is preferred at lower temp w a strong sterically hindered base? kinetic or thermodynamic enolate.
kinetic
if rxn is reversible then the kinetic product can revert to reactant and form thermodynamic product
which is preferred at higher temp w a weak small base? reversible. kinetic or thermodynamic enolate.
thermodynamic
enamine vs imine
enamine: double bond between carbons
imine: double bond between carbon and nitrogen
aldol condensation
- enolate form more nu than electrophilic carbonyl form
- carbonyl + base = enol
- C2 of enol attacks carbonyl carbon of a carbonyl
- oxygen of the second carbonyl get protonated
- 1,3 aldol formed
aldol + strong base and heat
- dehydration
- a,B unsat carbonyl
aldol + strong base + water
aldehyde (alcohol side) and ketone
- retro aldol rxn
