Spectroscopic studies of molecular interactions involving 5- substituted uracil donors and chloranil as an electron acceptor

Abstract

Electronic absorption and electron spin resonance spectroscopic measurements have been made on the interaction between uracil, 2- thiouracil, 5-substituted uracils and 2' -deoxyuridine as &lt;i&gt;n&lt;/i&gt;-donors and chloranil as &pi;-acceptor. The studies reveal that EDA complex of charge transfer type acts as precursor to the formation of uraci/uridinium free diradical canon and trichlorohydroxyquinone. The electronic absorption bands in the 615-625 nm range are attributed to red coloured trichlorohydroxyquinone while ESR signal is assigned to free diradical cation. The thermodynamic stability constants, <em>K</em>, for the various D-A systems, as determined from the Benesi-Hildebrand model, follow the ascending order, 5-methyluracil &lt; 5- arninouracil &lt;Uracil &lt;5-iodouracil &lt;2-thiouracil &lt; 5- bromouracil &lt; 5-nitrouracil.