3.3.8 Aldehydes and Ketones (A2)
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what is the functional group of an aldehyde?
C=O(H) on the end of a molecule
what is the functional group of ketones?
C=O in the central region of a molecule
how are aldehydes made?
primary alcohol - one carbon bound to the carbon with -OH oxidise - H+/K2Cr2O7 (sulfuric acid) orange—>green distillation
what is the aldehyde called which includes a benzene ring?
benzanal
how are ketones made?
oxidation of secondary alcohol H+/K2Cr2O7 (potassium dichromate) orange —> green under reflux
what are the properties of aldehydes and ketones?
C=O bond is polar dipole-dipole interactions between molecules higher boiling points than their counterpart alkanes - more energy needed to overcome intermolecular forces
what is the solubility like of aldehydes and ketones?
aldehydes and ketone with less than 4 carbons can dissolve in water because carbonyl group can hydrogen bond to water.
why can’t aldehydes and ketones with more than 4 carbons dissolve in water?
the larger the amount of carbons, the more non polar the molecule, this prevents molecule from dissolving
what state is methanal at room temperature?
gas
what state are short chain aldehydes and ketones at room temperature?
liquids (apart from methanal) with a characteristic smell
what is an example of a ketone used in a household item?
propanone found in nail varnish remover
what is benzaldehyde used for? why?
scenting soaps and flavouring foods smells of almonds
why do ketones have no fewer than 3 carbons?
the double bond oxygen has to be on neither end of the carbon chain
what is the lowest number of carbons in a ketone?
3
why is no numbering system needed for aldehydes?
R=O(H) has to be on either end of the chain
why are there no H bonds between propanone molecules?
no oxygen bonded to hydrogen
what reactions tend to happen with aldehydes/ketones?
REDOX nucleophilic addition - the delta positive carbon is susceptible to nucleophilic attack, carbonyl group unsaturated
why can’t we use the cyanide ion in the lab?
cyanide is toxic
what group are the products of reactions with cyanide ions in?
nitrile
why do we get a racemic mixture?
C=O bond is planar nucleophile can attack from either above or below the plane 50:50 chance of either happening so we get a 50:50 mixture of both enantiomers
why do racemic mixtures show no optical activity?
the rotation on plane-polarised light cancels out
what is oxidation?
loss of e- gain of oxygen loss of H
what is reduction?
gain of e- loss of oxygen gain of H
what does the oxidation of an aldehyde result in?
carboxylic acid