The Electronic Spectra and Nonaqueous Oxidation and Reduction Potentials of Azoxybenzenes, and Their Mutual Correlation

Abstract

Abstract The near-ultraviolet absorption spectra of various p,p′- and m,m′-disubstituted azoxybenzenes were recorded in aprotic and protic solvents. The PPP-SCFMO-CI calculation was used in analyzing the spectra and the solvent effect on them. The π-π* bands of azoxybenzene could be well interpreted on the basis of the electronic structure of benzaldehyde N-phenyl oxime (a nitrone). In addition, the half-wave potentials of reduction (E1⁄2red) and oxidation (E1⁄2oxd) were also measured in nonaqueous solvents. These electrochemical data and the above spectral data satisfied a good linear relation: (E1⁄2oxd–E1⁄2red)=k1·Eho→luUV+k2, this equation having been previously proposed by us. In the Appendix, we have discussed the physical meaning of the constant term, k2, from the quantitative standpoint, using a series of alternant hydrocarbons as a typical example. Finally, a good linear relation between the E1⁄2red or E1⁄2oxd values and the substituent constants was demonstrated and discussed in azoxybenzenes.