WAEC Chemistry 2010 Paper

Concept:Esters are named as alkyl alkanoate: the group from the alcohol is written first, followed by the name derived from the carboxylic acid.Explanation:The ester has the condensed structure $\mathrm{CH_3CH_2COOCH_2CH_3}$, which can also be written as $\mathrm{C_2H_5COOC_2H_5}$.To name it, break the molecule at the $\mathrm{-COO-}$ bond.The acid part is $\mathrm{CH_3CH_2COO^-}$, which comes from propanoic acid, $\mathrm{CH_3CH_2COOH}$.Therefore, this acid part is called propanoate.The group attached to the oxygen atom is $\mathrm{C_2H_5}$, which is the ethyl group.Now combine the names by placing the alkyl group first, followed by the alkanoate part.Thus, the IUPAC name is ethylpropanoate.Answer:B. ethylpropanoate