Substituent effects on the voltammetric studies of 2-oxo-1,2,3,4-tetrahydropyrimidines

The electrochemical oxidation of various substituted 2-oxo-1,2,3,4-tetrahydropyrimidines (THPMs) in acetonitrile has been studied using voltammetric methods at a glassy carbon electrode to investigate the steric and electronic effects of the substituents on the 1-, 4- and 5-positions of the heterocyclic ring. Analysis of the results presented in this study shows that the electronic nature and steric hindrance of the substituents, their positions and their orientations towards the heterocyclic ring, determine their effects on the oxidation peak potential. The electron detachment process in this study is also affected by the nature of solvent, which explains the extent of solvation of both neutral THPM and THPṀ+. Analysis of the computational results obtained at the DFT-B3LYP/6-31++G** level of theory suggests a mechanism in which the first electron removal occurs from the N1 atom. This process is followed by a fast proton removal, resulting in the formation of stable allylic and/or benzylic radicals which then undergo further oxidation to the 2-oxo-1,2-dihydropyrimidines (DHPMs).