Applications of proton magnetic resonance spectroscopy in the structural investigation of xanthones
Computed chemical shifts and coupling constants for xanthone in deuteriochloroform and trifluoroacetic acid are in agreement with experimental data at 60, 100, and 220 MHz. The increased dispersion of the signals at 220 MHz in deuteriochloroform shows four distinct aromatic proton signals which can be analysed directly by first-order methods. Fundamental parameters for xanthone in carbon tetrachloride, pentadeuteriopyridine, hexadeuterioacetone, and hexadeuteriodimethyl sulphoxide have also been measured. Additive diamagnetic shifts for ortho-, meta-, and para-hydroxy-, alkoxy-, and alkyl substituents have been determined empirically and experimental and predicted chemical-shifts for natural and synthetic xanthones are in agreement, providing steric hindrance of vicinal groups is considered. The influence of different solvents on chemical shifts and coupling constants has been correlated.