6.1.2 Carbonyl Compounds
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what are the 2 carbonyls
aldehydes and ketones
what are carbonyls
contain the carbonyl functional group C=O
what are aldehydes
• carbonyl functional group found at the end of the carbon chain • CHO
what are ketones
• carbonyl functional group is joined 2 to other carbon atoms in the carbon chain • CO • start with propanone
how do you name aldehydes
• add the suffix -al • don’t need to name aldehyde group, this is ALWAYS on carbon-1
how do you name ketones
• add the suffix -one • only needs to be numbered past 5 carbon atoms
what are aldehydes oxidised into
carboxylic acids
what are the reagents required for the oxidation of aldehydes
• acidified potassium dichromate ions • usually found with K2Cr2O7 and H2SO4 • oxidation agent shown via [O] • under reflux
what is the equation of oxidation of butanal
butanal + [O] ===> butanoic acid • (add reagents onto the arrow)
what happens to ketones when oxidised
ketones do not undergo oxidation reactions
what is the reactivity of carbonyls influenced by
the C=O bond
how is the C=O bond structured in carbonyls
• a sigma single bond between the C-O • and a pi-bond above and below the planes of the carbon and oxygen atoms
what is the difference between the C=C and C=O double bond
• the C=C bond is non-polar (electrophilic addition) • the C=O bond is polar
explain the polar C=O bond
• O is more electronegative than C • so the electron-density in the C=O bond lies closer to the O atoms • so C=δ+ and O=δ-
how does the polar C=O bond affect the reactivity of aldehydes
• can react with NUCLEOPHILES • via nucleophilic addition • as can attract them with the Cδ+
what is the reducing agent for carbonyls
NaBH4 - sodium tetrahydridoborate (III)
how are carbonyls reduced
• reduce to alcohols • usually using a warm carbonyl and NaBH4 • in an aqueous solution
what are aldehydes reduced to
primary alcohols
what is the equation for reduction of aldehydes
aldehyde + 2[H] ===> primary alcohol • need to add NaBH4 and H2O onto the arrow • e.g. butanal would go to butan-1-ol
what are ketones reduced to
secondary alcohol
what is the equation for the reduction of ketones
ketone + 2[H] ===> secondary alcohol • need to add NaBH4 and H2O on the arrow • e.g. propanone would go to propan-2-ol
what is HCN
hydrogen cyanide
what are the properties of hydrogen cyanide
• colourless, poisonous gas • boils slightly over room temperature • cannot be used safely in an open lab
what is used to provide HCN in a lab
• sodium cyanide • sulfuric acid • STILL hazardous