aldehydes and ketones Flashcards
whats a carbonyl group
which organics have them
C=O
aldehydes, ketones, c acids and co
c acid derivatives acyl chlorides and acid anhydrides can be attacked by water, ammonia, amines or alcohols (nucleophilic addition elimination, the mechanism of acylation)
the oxidation of what causes the formation of aldehydes/ ketones
1y alcohols form aldehydes (partial ox)
2y alcohols form ketones (full ox)
conditions: acidified potassium dichromate (ox agent; gets reduced), heat and distil
whats the ox of aldehydes
conditions
alcohol + [O] —> aldehyde
acidified (dilute s acid) potassium dichromate, heat and distill
aldehyde + [O] —> c acid
RCHO + [O] —> RCOOH
acidified (dilute s acid) potassium dichromate, heat under reflux
what two tests distinguish between aldehydes and ketones
Fehlings
Tollens
they are both redox reactions, where because the aldehyde can undergo further oxidation to c acids, it can reduce the reagents in either
how does tollens work, what is the test
(silver mirror)
a redox reaction between the aldehyde and Tollens’ reagent
reagent: [Ag(NH3)2]+
The silver ions in Tollens’ reagent are reduced to metallic silver (0 ox state). aldehyde acts as reducing agent. reduction of silver ions to metallic silver, it is deposited on the inside the test tube
CH3CHO + 2Ag+ + H2O —> CH3COOH + 2Ag + 2H+
how does fehlings work, what is the test
Fehling’s test detects aldehydes based on their ability to reduce copper(II) ions to copper(I) oxide in an alkaline medium. Aldehydes are readily oxidised to carboxylic acids, which reduces copper(II) to a reddish-brown precipitate of copper(I) oxide.
fehlings a and b give blue solution, copper 2. copper 1 in copper oxide is red. copper 2 gets reduced as aldehyde gets oxidised
CH3CHO + 2Cu2+ + 2H2O —> CH3COOH + Cu2O + 4H+
if alcohols can be oxidised to form them, then…
how do write eq
aldehydes can be reduced to 1y alcohols
and
ketones can be reduced to 2y alcohols
RIG, of e- and H, so in equations we just say [H] like in the ox reactions we say [O]
what are the conditions of aldehyde/ketone reduction to from alcohols
what mechanism is this reaction
NaBH4 in aq solution - source of nucleophilic :H- ions
RTP
nucleophilic addition
what happens in nucleophilic addition mechanism of aldehydes and ketones
- nucleophile (eg H-, CN-) donate LP to delta +ve C
- bond of C=O goes to O. now :O-
- electrophile (eg H+ (so need to add dilute acid)) accepts LP on :O-
- forming alcohol f group
what is the product of nucleophilic addition of aldehydes/ketones (carbonyl compounds) with KCN followed by dilute s acid at RTP
hydroxynitrile
addition of CN adds a nitrile group and branches out (ketone)/ extends (aldehyde) the C chain
then the addition of H+ from acid (the electrophile) onto the O makes it hydroxy
(nitrile has priority so suffix)
whats an enantiomer
pair of molecules that exist in two forms that are mirror images of one another but cannot be superimposed one upon the other
when can optical isomerism arise with these carbonyls
the nucleophilic addition of KCN then dilute acid to: aldehydes, and unsymmetrical ketones
unsymmetrical ketones?
this is to say that the C chain on either side of the C=O isn’t the same length. but if you have a chiral C then yer
what causes optical isomerism arise with these carbonyls
the planar C=O group on the aldehydes/ unsymmetrical ketones get attacked equally by KCN from either side of the C=O
there is equal chance of both enantiomers forming. there is no optical activity because racemic mixture
optical activity: ability of molecules (when just solution of one enantiomer) to rotate the plane of polarised light
