CONCERNING THE ACIDITY AND HYDROGEN-BONDING OF HYDROXYPHENANTHROPERYLENE QUINONES LIKE FRINGELITE-D, HYPERICIN, AND STENTORIN

The strongly enhanced acidity of the bay hydroxyl group as compared to the respective peri hydroxyl groups of fringelite D, hypericin, and s tentorin could be rationalized on the basis of a vinylogous carboxylic acid and was nicely corroborated by semiempirical calculations of the AM1 type. Experimental data obtained from several independent experim ental methods, like polarized absorption spectroscopy, hole burning, a nd isotope effects, as well as from semiempirical AMI and 6-31G level ab initio calculations conclusively pointed to dissymmetrical hydrogen bonding systems in both the peri and bay regions of the corresponding bay phenolate ions.