SPECTROSCOPIC STUDIES OF MOLECULAR-INTERACTIONS INVOLVING 5-SUBSTITUTED URACIL DONORS AND CHLORANIL AS AN ELECTRON-ACCEPTOR

Electronic absorption and electron spin resonance spectroscopic measur ements have been made on the interaction between uracil, 2- thiouracil , 5-substituted uracils and l-deoxyuridine as n-donors and chloranil a s pi-acceptor. The studies reveal that EDA complex of charge transfer type acts as precursor to the formation of uracil/uridinium free dirad ical cation and trichlorohydroxyquinone. The electronic absorption ban ds in the 615-625 nm range are attributed to red coloured trichlorohyd roxyquinone while ESR signal is assigned to free diradical cation The thermodynamic stability constants, K, for the various D-A systems, as determined from the Benesi-Hildebrand model, follow the ascending orde r, 5-methyluracil < 5- aminouracil <uracil <5-iodouracil <2-thiouracil < 5- bromouracil < 5-nitrouracil.