WAEC Chemistry 2017 Paper

Concept:Esters are named as alkyl alkanoates: the alkyl group attached to oxygen is named first, followed by the acid part with the suffix changed from $-oic$ acid to $-oate$.Explanation:The given ester is $\mathrm{C}_{4}\mathrm{H}_{9}\mathrm{COOC}_{3}\mathrm{H}_{7}$.It can be split into two parts: $\mathrm{C}_{4}\mathrm{H}_{9}\mathrm{COO}-$ and $\mathrm{C}_{3}\mathrm{H}_{7}-$.The part $\mathrm{C}_{3}\mathrm{H}_{7}-$ is the alkyl group, named as propyl.The part $\mathrm{C}_{4}\mathrm{H}_{9}\mathrm{COO}-$ is derived from the parent acid $\mathrm{C}_{4}\mathrm{H}_{9}\mathrm{COOH}$.Counting the carbonyl carbon, the acid chain has 5 carbon atoms, so the acid is pentanoic acid.When forming the ester name, $-oic$ acid becomes $-oate$, giving pentanoate.Therefore, the ester is called propyl pentanoate.Answer:The name of the compound is propyl pentanoate.Correct option: A. propyl pentanoate.