Systematics in the Electronic Spectra of Nucleoside Derivatives

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Abstract
In order to calculate accurately the orientation of the sugar relative to the base in the pyrimidine nucleosides from circular dichroism data, the localized nature of the electronic transitions in both the sugar and the base have been exploited. Within the matrix formalism of the theory of optical activity, the sugar is treated by the bond exciton theory without the resonance assumption. The chromophore is treated by a semiempirical self‐consistent field calculation from which the delocalization of each transition is extracted and then compared with the results of the bond exciton treatment. In three bands, there is excellent support for the SCF CI result, and these three are then used to draw conclusions regarding the molecular geometry. The one‐electron effect on the pyrimidine nucleoside circular dichroism is shown to be small. The manner in which transitions are localized in the various chromophores is then used as a basis for a systematical discussion of various nucleoside spectral properties.