CARBONYLS Flashcards
why are aldehydes and ketones described as unsaturated
they contain a carbon-oxygen double bond
tollens + aldehyde
forms a silver mirror
tollens + ketone
no reaction as ketone cannot be further oxidised
acidified K2Cr2O7 + aldehyde
orange –> green colour change
acidified K2Cr2O7 + ketone
no reaction as ketone cannot be further oxidised
what does the reduction of an aldehyde produce
1º alcohol
what does the reduction of a ketone produce
2º alcohol
what reagents do you use to reduce a carbonyl by nucleophilic substitution
NaBH4 in warm aq solution
carbonyl compound - nuc add. w/ nitrile ions
- reagents
- conditions
- nucleophile
- product
- eq.
- reagents = hydrogen cyanide HCN
- conditions = reflux in alkaline conditions
- nucleophile = cyanide ion CN:-
- product = hydroxynitrile
- eq.= CH3CHO + HCN –> CH3CH(OH)CN
- addition of HCN
- opical isomerism when CN-attacks from above vs below
why do the conditions need to be alkaline during nuc add. w/ nitrile ions
NaOH (aq) allows H+ to react w/ OH- to give water, .:. the equilibrium will shift to the right, producing more H+ and CN- (the nucleophile)
describe the mechanism for nuc add. w/ nitrile ions
STEP 1 :
CN- acts as a nucleophile and attacks the slightly positive C (from C=O)
1 of the C=O bonds break: e- pair goes to O
STEP 2:
A pair of e- used to form bond w/ H+
overall there has been an addition of HCN
2,4-DNPH + aldehyde
orange/yellow ppt forms
2,4-DNPH + ketone
orange/yellow ppt forms
test for carbonyls
2,4-DNPH –> orange/yellow ppt forms
2,4-DNPH = Brady’s reagent
test proves presence but does not identify aldehyde or ketone
how can you identify the carbonyl from the ppt formed after reacting it with Brady’s reagent/2,4-DNPH
recrystalise ppt in minimum amount of hot solvent
take the melting point of pure, dry crystal
compare to database + identify
