Aldehydes and Ketones Flashcards
(17 cards)
primary alcohol + excess Na2Cr2O7 makes …
a carboxylic acid
oxidation of a primary alcohol by a strong oxidizing agent will be produce a carboxylic acid
what intermediate does a primary alcohol undergo when treated with a strong oxidizer?
it goes through an aldehyde not a ketone
an enamine is made from an imine via
enamine vs imine
tautomerization
emines have double bond C=C
imines have double bond C=N
Tautomers (/ˈtɔːtəmər/) are structural isomers (constitutional isomers) of chemical compounds that readily interconvert. The chemical reaction interconverting the two is called tautomerization
the process increases stability
keto-enol tautomerism mechanism
between a keto (ketone or aldehyde) and structural isomer enol a C-C and O-H is formed for the enol and a C-O and C-H is removed for the keto
this is an equilibrium not resonance and cannot occur if a proton on the alpha carbon cant be removed
favors keto tautomer
catalyzed by acid or base
factors of enol stability; substituion, resonance, Hbonding, aromaticity
in keto-enol tautomerism which form is favored at equilibrium?
the keto form bc the carbonyl bond is stronger than the C=C
not because of resonance
enolate
Enolates can be formed through removing the proton on carbons adjacent to a carbonyl (i.e. the “alpha-carbon“). The resulting anions are much more stable than typical alkanes since the negative charge can be delocalized to the oxygen atom via resonance.
are enolates nucleophiles? how do they react?
aldol addition
nucleophillic carbon addition (amine or alcohol) + enolate alpha carbon of a carbonyl compound
More generally, an aldol addition is characterized as a nucleophilic addition to an aldehyde, ketone, or imine electrophile where the nucleophile is the a-carbon in an aldehyde, ketone, imine, ester, or thioester.
note that the aldol reaction results in a product in which a hydroxide g
enzymes that catalyze aldol reactions
aldolases
retro-aldol cleavage
in the retro-aldol cleavage reaction the β hydroxy group is deprotonated (step 1 above), to form a carbonyl, at the same time pushing off the enolate carbon, which is now a leaving group rather than a nucleophile.
when the carbon-carbon bond breaks, the electrons must have ‘some place to go’ where they will be stabilized by resonance. Most often, the substrate for a retro-aldol reaction is a β
-hydroxy aldehyde, ketone, ester, or thioester.
enolate as leaving group - resonance delocalization of the negative char
How is the fructose 1,6-bisphosphate aldolase reaction an example of retro aldol?
aldol condensation
two way reaction
aldol reaction + dehydration
creates a molecule with double bond and a carbonyl group and water by product
crossed aldol condensation
intramolecular aldol reactions
which molecule is least susceptible to nucleophilic attack?
larger, buliker groups on acyl side of carboxylic acid or derivates make it hard for nucleophilic attack due to sterics
