Graph‐theoretical identification of molecular formulae, empirical formulae, and molecular fragments

A given molecular formula (or a given set of atoms with/without electric charges) in chemistry can be represented in terms of positive integers (degrees in mathematical graph theory). Senior's graph‐theoretical criteria (1951) with respect to the representation judge whether or not the set is realized and connected as an undirected graph with multiple edges and without loops, or as a chemical structural formula. It is shown that the criteria can be interpreted as extended forms of the well known chemical theorems for analysing molecular formulae, and that repeated use of the criteria identifies both functional groups and molecular fragments in a given molecular formula. We hence conclude that the mathematical approach to the analysis of molecular formulae is very useful in chemistry teaching courses.