Assignment of individual signals of aromatic protons in the NMR spectrum of 6-substituted purines

Assignment of the resonances of ring protons in substituted purines is made by comparison with spectra of compounds in which one of these protons has been substituted by an alkyl group, and by application of the nuclear Overhauser effect to these derivatives in order to identify the signals of protons adjacent to the alkyl substituent. Chemical shifts are given for various ionic forms of the purines in deuterium oxide solution, as well as for the neutral forms.