ChemInform Abstract: THE EFFECT OF SUBSTITUTION ON PROTONATION SITES, EVIDENCE FOR PROTONATION AT N(3) IN N(7)‐SUBSTITUTED ADENINE

Abstract

Abstract Several experimental and theoretical studies have shown that N (1) is the first site for protonation in adenine and N (9)-substituted adenine derivatives. N (7) is considered the site for the second protonation to yield dipositive cations. Results are reported here which indicate that this protonation pattern is altered in N (7)-substituted adenine derivatives. In particular, an X-ray diffraction analysis of the structure of 7-methyladenine dihydrochloride, [C 6 N 5 H 7 ]Cl 2 , definitively shows that the sites for protonation are N (3), as opposed to N (1), and N (9). Theoretical calculations of the molecular electrostatic potential in various systems suggest that such changes in preferred protonation sites should be expected, in general, when a modification of the molecular structure creates adjacent sites with similar reactivity, such as the N (3) and N (9) sites in 7-methyladenine.