Ultraviolet photoelectron studies of 5‐halouracils

Abstract

Abstract Ultravoilet photoelectron spectroscopy has been employed to exmamin the valence electronic structure of 5‐fluorouracil, 5‐chlorouracil, 5‐bromouracil, and 5‐iodouracil. Photoelectron bands associted with the three highest π orbitals and the two oxygen atom lone‐pair orbitals were assigned by a comparison to similar bands observed in the photoelectron spectrum of uraciul. Bands arising from the halogen atom lone‐pair orbitals were assigned by comparing the present results with photoelectron spectra measured for halobenzenes, and by considering the linear dependence of halogen atom lone‐pair ionization potentials upon halogen atom electronegativities. The present spectroscopic results have been compared with results from studies of association constants of 5‐halouracil–adenine complexes. This examination in dicates that the complex association constants incresase as the ionization potentials of the highest occupied π orbital and the halogen atom lone‐pair orbitals of th halouracils decrease.