Ionization constants of all seven positional isomers of quinolinesulfonamides and quinoline-N,N-dimethylsulfonamides

The pKa values of isomeric sulfamoylquinolines 2a–8a and N,N-dimethylsulfamoylquinolines 2b–8b were determined by means of a UV–VIS spectroscopic method that uses absorbance diagrams, at constant ionic strength (0.15 M). For sulfamoylquinolines 2a–8a two pKa values – for basic function (Nring: −0.31 to 3.36) and for acid function (SO2NH2 group: 8.89–10.34) but only one in the case of N,N-dimethylsulfamoylquinolines 2b–8b (−0.05 to 3.07) – were obtained. The full geometry optimization in the 6–311 + G(d) basis set and the NBO population analysis were performed. Correlation between the experimentally determined and theoretically calculated (Sparc program) of pKa values as well as the differences between the calculated NBO population values for neutral and ionic forms were found for compounds 2a–7a and 2b–8b.