Figure 1.

First data set of titratable molecules involves 81 molecules in nineteen different molecular families (A–S). The detailed data are listed in Tables S1–S7 of the Supporting Information. The number of molecules of a specific family is given after the one-letter family name. The molecules are displayed in the protonated state with titratable protons in green color, whereas the other polar hydrogens are displayed in black. For the families O and P only one resonance structure is shown, but, all displayed hydrogen atoms are equivalent and titratable. Nonpolar hydrogens are not displayed. For the families R and S protonation of the carbon atom C2 and C3, respectively, converts the double bond between the two carbon atoms to a single bond. As a consequence the excess positive charge is localizes at the carbon atom, which is not protonated. The formal charge localized at the titratable hydrogen is denoted as a superscript. Oxygen, nitrogen, and sulfur atoms are highlighted in red, blue, and yellow color, respectively.