The structural formula of an ester is:

The structural formula of the ester is of the compound ethyl ethanoate (CH₃COOC₂H₅).

Esters are formed by the process of esterification when an alcohol reacts with a carboxylic acid in the presence of concentrated sulphuric acid.

(a) The formula of the acid (acetic acid) is CH₃COOH.

(b) The formula of the alcohol (ethanol) is CH₃-CH₂-OH.

The chemical equation is given below:

$CH_3COOH + CH_3CH_2OH \xrightarrow {Conc. H_2SO_4} CH_3COOCH_2CH_3 + H_2O$