1. ESTERS

2. What is an ester? Responsible for tastes and odours.
Contain the ester linkage
Made from an alcohol and a carboxylic acid.
Since the C=O group is polar and has the ability to hydrogen bond, these compounds will have higher melting and boiling points than the corresponding hydrocarbon and they will be soluble in water

3. NAMING
Use the “yl” form of the alcohol proceeded with the “oate” form of the carboxylic acid.
i.e. “alkyl oate”
Examples

4. Reactions of Esters
1. Preparation
2. Hydrolysis (reverse of 1)

5. For the above reactions, if there is an excess of the alcohol and carboxylic acid, reaction 1 is favoured and if there is an excess of water, reaction 2 will be favoured.
3. Irreversible Hydrolysis
Since these conditions produce a stable carboxylate
ion, the reaction is not reversible

6. Waxes
Waxes are mixtures of esters having carbon chains in the range of 16 to 34 carbons on each side of the ester linkage.
Since the hydrocarbon chains are so long, waxes
are very water repellant.
Biological Importance: fruit, leaves, insects

7. Fats and Oils
Fats and oils are triesters of glycerol that contain at least one fatty acid.
Fatty acids are carboxylic acids that contain carbon and having varying degrees of unsaturation
glycerol + 1 fatty acid  monoglyceride + water
glycerol + 2 fatty acids  diglyceride + water
glycerol + 3 fatty acids  triglyceride + water

8. Fats in Plants
The hydrocarbon chains are unsaturated with 1,2, or 3 C=C bonds.
The double bonds reduce the intermolecular forces by causing “kinks” in the chain resulting in lower melting and boiling points.
For this reason the fats are generally liquid (oils)
Since the double bonds provide a site for reactions, the break down of unsaturated fats is more effective (i.e. less cholesterol).
The double bonds are easily oxidized meaning edible oils will go rancid (i.e. spoil) and oil based paints/varnish will crosslink to produce tough films.

9. Fats in Animals The hydrocarbon chains are fully saturated.
The chains are fairly straight allowing for close packing and greater intermolecular forces.
Due to the lack of unsaturation, they are not broken down easily by the body and can cause the build up of cholesterol.
Solids at room temperature.

10. Salicylates Contain salicylic acid.
Most common is acetyl salicyclic acid “ASA” (AKA aspirin) which is used for pain relief and as an antiseptic.