an official format of the data is under review, and is expected to be posted online in the near future. Both data sources were checked for errors and occasionally corrected. A more detailed discussion of the curation process is in the Methods section. The pK a distributions in D2A-pKa vary significantly across different solvents, as shown in the Figure . For example, in water, pK a values mostly fall within 0 to 14, but pK a data in dimethyl sulfoxide (DMSO) is more widely distributed. These differences largely reflect the measurable pK a ranges in each solvent (determined by the solvent's autoprotolysis constant) as well as the different selections of acid types that have been measured and compiled in each solvent. For example, carboxylic acids make up nearly 40% of the pK a data in water (and contribute to the peak near 4 pK a units), but only 12% of the pK a data reported in DMSO. The acidities of many C-H bonds have been measured in DMSO;