Key to the accurate determination of the polar interaction descriptors is the availability of K data for partition systems with water as a partition phase because water is a strong H-bond donor and acceptor phase and thus the corresponding K values are sensitive to the H-bonding properties of the solute. In particular, at least one solvent/water or air/water data is required to determine B because there is no commonly used GC phase that is a significant H-bond donor. In the data set, KHxd/w is sensitive to both A and B and Kow is sensitive to B. However, KHxd/w and Kow data are not available for all PFAS. To increase the number of PFAS for which descriptors can be determined, the following assumptions were made. First, PFAS that have the same nonfluorinated structure and differ only in the perfluoroalkyl chain length share the values of S, A, and B. Examples of this case are 4:2, 6:2, 8:2, 10:2, and 12:2 FTOHs. Second, A and/or B were set to 0 if the compound does not have a functional group that can form an H-bond in the respective manner. For example, A and B were set to 0 for perfluoroalkanes (PFAs), perfluoroalkyl iodides (PFAIs), and FTOs; A was set to 0 for X:2 fluorotelomer iodides (FTIs), acrylates (FTACs), and methacrylates (FTMACs), B was set to 0 for 1H,8Hperfluorooctane (1,8-DHPFO); and. All these assumptions are tabulated in the SI (Table ).