Carbon-unbalanced reactions cannot be meaningfully handled at the level of sum formulas. Instead, it is necessary to make use of the structures of reactant and product molecules. To this end, we represent both the reactants and the products of a reaction as graphs whose connected components are the molecules. In these graphs, vertices are labeled by atom types and edges correspond to chemical bonds, annotated by their bond type. Since reactions with carbon atoms missing on the reactant side are treated in the same way as reactions with missing carbon on the product side, we fix the notation as follows: Let X and Y be the graphs with the larger and smaller number of carbons, respectively. Moreover, we write X = {X 1 , X 2 , . . . , X k } for the set of connected components of X. Assuming that all missing carbons belong to one connected compound Y * missing on the Y -side of the reaction, we can conclude that Y * is in essence a part of some X i . In order to identify this part, we compute, for each X i ∈ X , a maximum con-