This section discusses a potential future method to solve reaction completion. Using an atom mapping tool to understand the atom rearrangements from the reactants to the products, the unmapped fragments in the reactants could be detected. These fragments themselves could be potential missing products of the incomplete reactions, coming from the cleavage of the reactants, or could be recombined to form new product molecules. Figure (a) shows an example reaction completed by this method. Using the atom mapping tool RXNMapper, it is known that in the anion of the reactants, only the carbon atom, marked as "C[:1]", is mapped into the products. Therefore, it is very likely that the carbon-carbon bond connected to the carbon atom is broken to form another anion product shown in the red box in Figure However, currently this fragment method cannot be applied to all reaction records but demonstrated here as a potential future method. This is because firstly, there is no perfect atom mapping tool which always gives ground truth mapping results, from which the unmapped fragments are always uncertain. Secondly, the unmapped fragments could undergo further cleavage or recombination steps, which at this stage could only be manually examined. With further development of this method in the future, this could be a third-tier method if the reaction completion fails from ChemBalancer and ChemMLM predictions.