Conformer sampling. The hydrocarbon dataset presented herein contains molecules with diverse structural elements (see Fig. for 10 randomly selected examples). While the enumerated 2D molecular graphs contain information on molecular bonding, they do not fully determine the molecular geometry, e.g. with respect to relative configurations around rotatable single bonds. As an example, 115.888 (53.046) of the contained molecules incorporate at least 2 (4) rotatable bonds, with a maximum of 5 rotatable bonds occuring overall. We thus expect a significant conformational flexibility for these molecules. This flexibility can influence the ML predictions of λ in two ways. First, the reference λ values may depend on the conformer and second, the ML prediction of λ is based on a representation derived from a 3D molecular geometry. To arrive at an internally consistent procedure when comparing among different molecular systems, we therefore focus on the lowest energy conformers that we can identify for each molecular system.