ON THE RELATIVE STABILITY OF DIOXO DERIVATIVES OF PHENANTHRO[1,10,9,8-OPQRA]PERYLENE RELATED TO THE TAUTOMERS OF HYPERICIN

In order to simplify the problems encountered in the study of the stab ility order of the tautomers of hypericin, we examined the structural factors influencing the stability of the respective dioxo derivatives of the parent benzenoid hydrocarbon phenanthro[1,10,9,8-opqra]perylene . It is shown that the stability order of these dioxo derivatives is e ssentially the same as that of the corresponding tautomers of hyperici n. This corroborates the earlier opinion that the relative stability o f the tautomers of hypericin is primarily determined by differences in pi-electron conjugation and only to a lesser extent by steric effects of the oxo groups in positions 3 and/or 4.