On the Tautomers of Hypericin

摘要: Hypericin has 16 theoretically conceivable tautomers (10 with and 6 without Kekule structural formulas). AM1 calculations show that two factors determine the relative stability of tautomers. The dominant factor is mode conjugation π-electrons. A less pronounced, yet significant, steric repulsion carbonyl and/or hydroxy groups in positions 3 4. Among equal π-electron conjugation, least stable are those having tautomer Q(7, 14), 7 14, far most one; next –Q(1, 7) 13) – have by some 40 kJ/mol higher energies, followed Q(3, 7), Q(8, 13), Q(1, 6) energies 60, 70 above energy etc. values hypothetical structures lie 150–200 14); therefore, these no practical relevance.