Pteridine studies. Part XXXIII. Equilibria between 3,4-hydrated and 5,6,7,8-dihydrated cations

Abstract

Proton magnetic resonance studies indicate that the 3,4-hydrated cation of pteridine in aqueous solution gradually reaches equilibrium with a 5,6,7,8-dihydrated cation (3,4-hydrate, 21%, 5,6,7,8-dihydrate, 79% at pH 2). With pteridine and its derivatives, the proportions of the two cations at equilibrium appear to depend upon the effectiveness of resonance stabilisation in the respective species. Reactions previously attributed to reversible ring-opening are shown to involve only a change of hydration site.