DEUTERIUM-ISOTOPE EFFECT ON H-1 AND C-13 CHEMICAL-SHIFTS OF INTRAMOLECULARLY HYDROGEN-BONDED PERYLENEQUINONES

The primary and secondary deuterium isotope effects on proton and carb on chemical shifts were measured for a number of natural pigments and their derivatives, which contain the perylenequinone system and presen t a phenol-quinone tautomerism, cercosporin 1, isocercosporin 2, phlei chrome 3, isophleichrome 4, cladochrome E 5, elsinochromes 6-8, hypocr ellin 9, noranhydrocercosporin 10 and noranhydrophleichrome 11. Deuter ium isotope effects on protons were also measured for 1,4-dihydroxyant hraquinone 12, methyl xy-9,10-dioxo-9,10-dihydroanthracen-2-yl)butanoa te 13,N-acetyldaunomycin 15, daunomycinone 16, naphthazarin 17 and a n umber of intramolecularly hydrogen-bonded enols from beta-diketones, b eta-ketoesters and omicron-hydroxyacyl aromatic compounds 19-24. The p rimary isotope effects Delta delta(H-1,H-2) on OH proton shift and H-1 chemical shifts of OH groups are correlated and can be used to estima te the strength of the hydrogen bonds in solution. The secondary isoto pe effects on proton and carbon nuclei are transmitted along the whole extended conjugated perylenequinone system. Long-range effects over e leven bonds and over seven bonds were observed in compounds 1-11 and i n 12-18. The perturbation of the equilibrium due to the presence of de uterium was considered and calculations were performed in order to eva luate the amount of this contribution to the isotope effect. The varia tion with temperature of primary and secondary effects, from 25 degree s C down to -70 degrees C, was studied for compounds 1, 3, 6, 12 and 1 7, and for acetylacetone 22 and benzoylacetone 23. Parameters from a n umber of X-ray analyses, for example the O ... O distances (as suggest ed by Gilli et al., J. Am. Chem. Sec., 1991, 113, 4917), gave evidence of a substantial parallelism between the liquid and the solid phase. The strength of the hydrogen bond in perylenequinones depends on the p lanarity of the two naphthalene units rather than on the distortion of the polycyclic ring.