To generate the structures of the reactants and products, SMILES representations of the molecules were first generated from SMILES subgraphs of the NacNacGa=NR core and the R 1 and R 2 substituents. In the next step, graphs were converted to 3D atomic structures using the ghemical force field implemented in OpenBabel . The structures were then optimized using DFT so that the root mean square and maximum norm of the gradient are below 0.0003 E h a 0 -1 and 0.000 45 E h a 0 -1 , respectively.