An ester is a molecule containing an ester link, $-COO-$.

Esters names are determined from the carboxylic acid and the alcohol they are formed from.

→ ‘alcohol’ -yl ‘carboxylic acid’ -anoate

In a condensation reaction, two molecules are joined together with the elimination of a small molecule.

Esters are formed by a condensation reaction between an alcohol and a carboxylic acid.

When an ester link is formed by the reaction between a hydroxyl group and a carboxyl group, the small molecule eliminated is water.

In a hydrolysis reaction, a molecule reacts with water to break down into smaller molecules.

Esters can be hydrolysed to produce an alcohol and a carboxylic acid.

Esters are used as flavourings and fragrances as many have pleasant, fruity smells.

Esters are also used as solvents for non-polar compounds that do not dissolve in water.

Edible fats and edible oils are esters formed from the condensation of glycerol (propane-1,2,3-triol) and three carboxylic acid molecules.

propane-1,2,3-triol

The carboxylic acids used to form edible fats and oils are known as ‘fatty acids’ and can be saturated or unsaturated straight-chain carboxylic acids, usually with long chains of carbon atoms.

Edible oils have lower melting points than edible fats.

The greater the degree of unsaturation of fats/oils, the lower the melting point.

→ If the fatty acids are mostly saturated then the substance will likely be solid at room temperature and be termed a fat.

→ If the fatty acids are more unsaturated then the substance will likely be a liquid in room temperature and be termed an oil.

Double bonds in fatty acid chains prevent oil molecules from packing closely together, so the greater the number of double bonds present, the weaker the van der Waals forces of attraction.

Unsaturated compounds quickly decolourise bromine solution.

The bromine molecules add across the carbon–carbon double bonds in an addition reaction.

The greater the number of double bonds present in a substance, the more bromine solution can be decolourised.

→ The general formula for carboxylic acids is $C_nH_{2n + 1}COOH$ or $C_nH_{2n}O_2$. When the fatty acid is joined to glycerol then the $COOH$ is no longer present, so the first formula should be used and the $H$ to $C$ ratio considered as $C_nH_{2n + 1}$. However when a full fatty acid or carboxylic acid is presented then the latter formula should be used, and the $H$ to $C$ ratio considered as $C_nH_{2n}$.