Cyclic voltammetric and DFT computational studies of 3,5-disubstituted 4,5-dihydro-1,2,4-oxadiazoles: Steric and electronic effects

Abstract

Cyclic voltammetry, UV-vis spectroscopy and (TD)DFT/6-311++G(d,p) computations are applied to investigate electronic and steric effects of substitutions in a series of 3,5-disubstituted 4,5-dihydro-1,2,4-oxadiazoles (DHOZs). Compared to the σ-electron-donating/accepting substitutions on the C5-position, the π-electron-donating/accepting substitutions on the C3-position have larger effects on the frontier molecular orbitals energies, and consequently, on their oxidation peak potentials and UV-vis transitions. Furthermore, the σ-/π-electron-donating/accepting effects of substitution are larger for the LUMO energies. The trend of the results of the computational UV-vis spectra are in agreement with that of the experimental data. The frontier molecular orbitals and molecular electrostatic potential (MEP) surfaces of the optimized structures 1, 4 and 11, as representative, shows that the electrochemical oxidation occurs mainly from the heterocyclic ring, especially the N4 atom having lone pair in the sp3 orbital.