¹H, ¹³C and ¹⁵N NMR observations on the protonation of 1‐ and 3‐deazapurine

Abstract

Abstract Using 1 H, 13 C and 15 N NMR it has been concluded that 3‐deazarpurine protonates exclusively at N‐1 with a p K of about 5.6. The base exhibits rapid tautomerism with proportions of 70:30, with the N–7‐H tautomer in the majority. The salt exists predominantly as the N‐7‐H tautomer. 1‐Deazapurine protonates essentially in a 1:1 ratio at N‐3 and at the imidazole ring, with a p K of about 3.1. This base also exhibits rapid tautomerism with proportions of 30:70, this time with the N‐9‐H in the majority. The salt also exists in a tautomcric mixture with approximately equal proportions. One form has N‐3 and N‐9 bearing hydrogens and the other has N‐7 and N‐9 bearing hydrogens.