ELECTRONIC-SPECTRA OF SOME PTERINS AND DEAZAPTERINS

The electronic absorption spectra of some derivatives of pterin and N5 -deazapterin are analysed using the CNDO/S-CI method, including allowa nce for solvent shifts. These calculations give good agreement with th e spectra, which may be assigned to a group of pi<--pi transitions. T here are some differences between calculated values for gas-phase and solution models but their general level of conformity with experiment is similar. Band shifts caused by methyl substitution, protonation and replacement of ring nitrogens are investigated, and a number of struc tural and spectroscopic problems are addressed. The spectral predictio ns agree well with experimental assignments for tautomeric forms and p rotonation sites for known compounds, and predictions are made for the spectra of N8-deazapterin and N5,N8-dideazapterin which have not been reported.