Exploring the relationship between the conformation and pKa: can a pKa value be used to determine the conformational equilibrium?

Four substituted cis and trans-4,5-dihydroxyhexahydropyridazines that were expected to undergo pH induced conformational switching were synthesized and carefully investigated by NMR analyses and calculations. For two of the compounds a large difference in pKa existed between the two possible chair conformers and for one compound this resulted in conformational switching as a result of pH change. For the first time it is shown that the pKa directly reflects the conformational equilibrium of conformers.