الفهرس 
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Abstract
UV spectroscopy has continuously played a major role in the investigation of the properties and structure of nucleic acid bases and their derivatives. Pyrimidine and its deri- vatives are of great biochemical interest. Their absorption spectra have been extensively investigated especially in media of varying pH values. The structural significance of the spe- ctra of these compounds has been also critically studied in connection with a search for some relationship between elect- ronic structure and chemotherapeutic activity.
The study of the electronic structure, tautomeric pro- perties and optical properties of naturally occurring pyri Didines is a problem of great interest in molecular biology. The knowledge of these properties provide important informa- tion for understanding energy transfer, photochemistry, sagne- tic circular dichroism, and other properties of DNA, RNA, and related model systems. Here, in this chapter we will present
a concise review of some of these problems.
1.1. Studies on Tautomeric Equilibria and Spectra of Uracil
During recent years a very large amount of work has been carried out, both experimentally and theoretically, in order to elucidate the qualitative and quantitative aspects of pyrimidine tautomerion and to determine the physicochemical properties of the obser vable tautomeric forms of these molecules. Among the various.