TOWARD THE PHOTOSTABILITY MECHANISM OF INTRAMOLECULAR HYDROGEN-BOND SYSTEMS .4. 3(5)-(1'-HYDROXY-2'-NAPHTHYL)PYRAZOLES AND 3(5)-(2'-HYDROXY-1'-NAPHTHYL)PYRAZOLES

Two new families of compounds, the 3(5)-(1'-hydroxy-2'-naphthyl)pyrazo les (a series) and the 3(5)-(2'-hydroxy-1'-naphthyl)pyrazoles (b serie s), have been synthesized and fully characterized. The use of NMR (H-1 and C-13) and UV (absorption and emission) spectroscopies in differen t solvents led us to determine the major tautomers, the coplanarity of both rings (naphthyl and pyrazolyl) if present, and the existence of hydrogen bonds. The photostability of a representative set of such der ivatives was also determined, showing that the existence of an intramo lecular hydrogen bond (IMHB) is not an essential condition for providi ng UV stability. Moreover when such an IMHB is present in the molecule , the photostability is not dependent on whether the proton is transfe rred or not.