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what is the functional group of aldehydes?
-CHO containing a carbonyl group (C=O)
how are aldehydes formed?
initial oxidation and distillation of primary alcohols
Oxidation of aldehydes
oxidise to produce carboxylic acids
in presence of acidified potassium dichromate
test for aldehydes
tollens reagent
fehlings solution
positive result for Tollen’s test
silver mirror forms
positive result for Fehling’s test
brick red precipitate forms
functional group of ketones
carbonyl group (C=O)
how are ketones produced?
oxidation of secondary alcohols with acidified potassium dichromate
oxidation of ketones
no further oxidation
Mechanism name of reduction
nucleophilic addition
reagents and conditions used in reduction
NaBH4 under aqueous conditions
what does the reduction of an aldehyde form?
primary alcohol
what does he reduction of a ketone form?
secondary alcohol
what is the nucleophile in reduction of aldehydes and ketones?
H- ion / hydride ion
What is produced when aldehydes and ketones undergo nucleophilic addition with CN- ions?
hydroxynitriles
why is nucleophilic addition with CN- ions good?
extends the carbon chain by 1 carbon
Why is KCN often used in nucleophilic addition rather than HCN?
HCN is a gas so hard to store and reacts to produce dangerous byproducts
reagents used when aldehydes/ketones react with cyanide ions?
KCN and H2SO4
how can the reduction of an aldehyde by nucleophilic addition produce a racemic mixture?
carbonyl group is planar
it can be attacked from either side
there is a 50% chance of each side of the C=O bond being attacked
an equal amount of each enantiomer is formed
Do ketones produce a racemic mixture when reduced by nucleophilic addition?
symmetrical ketones don’t as there is no chiral carbon
asymmetrical ketones produce a racemic mixture as the product can be in the form of 2 enantiomers
why are aldehydes and ketones reactive?
the carbonyl bond is strong but still reactive due to its polarity
Intermolecular forces present between aldehyde and ketone molecules
dipole-dipole forces
What is the boiling point of aldehydes and ketones like compared to alkanes with a similar Mr?
relatively high
What is the boiling point of aldehydes and ketones like compared to alcohols with a similar Mr?
relatively low
natural state of aldehydes and ketones
methanal is a gas at room temperature
all other aldehydes and ketones are liquids
solubility of aldehydes and ketones
short chain are soluble
long chains aren’t
why do nucleophiles attack carbonyl groups?
carbon is slightly positively charged
can a ketone be chiral?
no
