Final answer:
The functional group of an ester consists of a carbonyl group bonded to an alkoxy group, represented as -C(=O)-O-R'. It is formed by the reaction of a carboxylic acid and an alcohol, where the acid's hydroxyl hydrogen is replaced by an alkyl group.
Step-by-step explanation:
The functional group of an ester is characterized by a carbonyl group (a carbon-oxygen double bond, C=O) adjacent to an alkoxy group (-OR'), where 'R' is typically a hydrogen or a hydrocarbon chain and 'R'' must be a hydrocarbon chain. This forms a distinctive -C(=O)-O-R' structure. The presence of these polar bonds contributes to the polar nature of esters. The general formula for an ester can be represented as R-C-O-R', where R is the acyl group and R' is the alkoxy group. Esters are created through a reaction between a carboxylic acid and an alcohol, resulting in a molecule where the hydrogen atom of the hydroxyl group in the acid is replaced by an alkyl group from the alcohol.
For instance, if we look at ethanoic acid (acetic acid) and compare it to methyl ethanoate (methyl acetate), we see the functional group difference. In ethanoic acid, we have the -COOH group, where the hydrogen is available for reactions such as forming ionic salts with bases. Conversely, in methyl ethanoate, the hydrogen is replaced by a methyl group, hence forming the ester linkage -COOCH3.