Esters are a class of organic molecules that can have a fruity or flowery aroma. The structure of an ester is a carbonyl with an alkyl or aryl group on one side and an oxygen bound to another alkyl or aryl group on the other side.
Depending on the alkyl or aryl groups, the ester can take on many different characteristics. For example, the reaction of glycerol and three fatty acids, which are carboxylic acids with long alkyl chains, results in a triglyceride, which has three ester groups. The long alkyl chains from the fatty acids give triglycerides a very high molecular weight. In contrast, simple esters have a low molecular weight and small functional groups.
The smells and flavors of fruits and flowers are attributed to simple esters. Even small changes to the structure of a simple ester greatly affect its fragrance. For example, changing a hydroxyl group to an amine changes the scent of this ester from wintergreen to grape. Similarly, propyl acetate smells like pears, while butyl acetate, which has only one more carbon in its chain, smells like apples.
One common way to make an ester is Fischer esterification, where a carboxylic acid and an alcohol react in the presence of an ac
