We used a subset of the topological and functional group filters described in and implemented them using SMARTS. With this filter set, strained ring systems, such as small fused / spiro rings or complex bridgeheads shared by multiple rings, were filtered out. Functional group filters exclude volatile and rather unaccessible functional groups such as peroxides or allenes. The post-processing steps defined in Table of also included the conversion of functional groups to enrich chemical space. This was omitted since we aim to characterize the crossover products without further modification. Moreover, we skipped checks of atomic volume. Instead, we directly considered 3D embedability using the rdkit implementation of basic knowledge informed Experimental-Torsion Distance Geometry (ETGK) . The method attempts to place a molecule in 3D space such that known bond length, bond angles, and torsion angles for bonds are respected. If this is not possible, the violations are recorded.