Structure of esters
To make an ester, a hydrogen atom must be removed from the hydroxyl group (–OH) of the alcohol.
The –OH portion of the acid's carboxyl group must also be removed. The hydrogren atom and the -OH combine to form a water molecule (H2O).
\(propanol + ethanoic\,\,acid \rightleftharpoons propyl\,\,ethanoate + water\)
This same change can be represented using shortened structural formulae:
\(CH_{3}CH_{2}CH_{2}OH+CH_{3}COOH\rightleftharpoons CH_{3}CH_{2}CH_{2}OOCCH_{3}+H_{2}O\)
When looking at the structure of an ester, you can easily name it. Remember that the C=O part of the molecule came from the acid.
In the molecule below, the ester link (-COO) separates the two parts of the molecule.
Since the C=O came from the parent acid, there were four carbon atoms in the acid molecule (butanoic acid) and two carbon atoms in the parent alcohol (ethanol).
This ester is called ethyl butanoate.
The names and structures of some other esters are shown below.
