aldehydes and ketones (3.3.8)
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what chemical tests can be used to distinguish between aldehydes and ketones?
Tollen’s reagent and Fehling’s solution
what are aldehydes reduced to and what are the conditions and reagents for this process?
• primary alcohols • NaBH4 in aqueous solution
what are ketones reduced to and what are the conditions and reagents for this process?
• secondary alcohols • NaBH4 in aqueous solution
how can a reducing agent be represented?
[H]
what are the reduction reactions of aldehydes and ketones an example of?
nucleophilic addition
why does a nucleophile react with an aldehyde and not an alkene?
• the nucleophile is attracted to the partially positive C atom on the aldehyde • alkenes contain an electron rich C=C bond • the nucleophile is repelled by this bond
what does carbonyl refer to?
the C=O group
what is produced in the nucleophilic addition reaction of a carbonyl compound with KCN followed by dilute acid?
a hydroxynitrile
what do aldehydes and unsymmetrical ketones do when they react with KCN followed by dilute acid?
form mixtures of enantiomers
why can a nucleophilic addition reaction with KCN followed by a dilute acid produce a mixture of enantiomers?
• there is a 50% chance the nucleophile will attack above the C and a 50% chance it will attack below • this can produce optical isomers where there are 4 groups or atoms surrounding a chiral C atom • a racemic mixture forms which is a 50:50 mixture of the two optical isomers • the racemic mixture is optically inactive • the angle of rotation of plane polarised light in a clockwise direction caused by one enantiomer is cancelled out by the angle of rotation in an anticlockwise direction caused by the other enantiomer
what is the overall equation for the reduction of propanal to propan-1-ol using aqueous NaBH4?
CH3CH2CHO + 2[H] -> CH3CH2CH2OH
what is the overall equation for the reduction of ethanal using KCN followed by dilute acid and what is the name of the product?
CH3CHO + HCN -> CH3CH(OH)CN 2-hydroxypropanenitrile
what hazard is associated with the use of KCN?
it is toxic