3.8&9 The Carbonyl Group

C=O

Aldehyde - RCHO - ethanal - always on the 1st carbon Ketone - RCOR - propanone - in the middle of the carbon chain

C=O bond is strongly polar Therefore permanent dipole dipole forces are present Leading to relatively high boiling points Solubility decreases in water as the carbon chain increases

Aldehydes are oxidised to carboxylic acids using reflux and acidified potassium dichromate VI Ketones cannot be oxidised as the c-c is too strong

Aldehyde heated with Fehlings solution turns brick red Ketones give no reaction (stay deep blue) Aldehyde heated with tollens reagent forms a silver mirror on the test tube The aldehyde is oxidised, silver is reduced Ketones give no reaction

Nucleophilic addition

CN and OH On the carbon where the double bond O was

In CN the ‘N’ is alway on carbon 1 so it is likely there are side chains when naming

A racemate can form With an aldehyde and an asymmetrical/chiral ketone

Symmetrical/non-chiral ketones

The first arrow goes from the lone pair on the CN- and attacks the C (with the double bond O) And the second arrow goes from the middle of the double bond C=O on to the oxygen

Then arrow goes from the lone pair on the oxygen to the H+ ion The final product is an OH group in replace of the double bond O And a CN group attached on the same carbon

A carboxylic acid forms

NaBH4 In methanol or aqueous conditions

The first arrow goes from the lone pair on a H- ion to attack the C The second arrow goes from the middle of the C=O bond to the oxygen Second stage: The arrow goes from the lone pair of the O- to a H+ ion Forming an alcohol

Asymmetrical ketones can produce racemates Symmetrical ketones and aldehydes do not form racemates

O || R-C - O - H RCOOH At the end of the carbon chain Ends in -oic acid

The OH group in carboxylic acids is more acidic that the OH group in alcohols

They form hydrogen bonds with water and themselves (in the solid state) Methanoic acid to butanoic acid (all 4) are soluble in water Higher boiling points than alkanes of similar Mr They have characteristic smells

Measure their melting point and comparing them to a table of values of known melting points We can use a thiele tube or do it electrically

The H+ ion from the OH group is lost leaving a negative carboxylate ion The negative charge is shared over the whole carboxylate group This delocalisation makes the ion more stable

Carboxylic acids are weak but strong enough to react with sodium hydrogencarbonate NaHCO3 This releases CO2 (also ester and water produced)

O || R - C - O - R RCOOR With COO in the middle

Based on the parent acid Ethanoic acid -> ethanoates First part: methyl, ethyl etc.. comes from the chain attached to the O Second part: methanoate, ethanoate etc… comes from the chain attached to the carbon (includes the carbon in the COO)