The Carbon-13 NMR Spectra and Electronic Structure of 3<i>H</i>-Phenoxazin-3-ones

Abstract

Abstract The 13C NMR chemical shifts of 3H-phenoxazin-3-one (1) and eighteen of its derivatives are reported. The chemical shifts of 1 can be explained in terms of a successive polarization of the π-conjugated framework by an electron-withdrawing carbonyl group and a π-donating ether oxygen. The principal factor solution for the chemical shifts of the 2-substituted 3H-phenoxazin-3-ones suggests that the first and the second factors collectively controlling the 2-substituent effect are electronic and steric effects, respectively. A dual substituent parameter analysis elucidated the transmission modes of the polar and resonance effects of the 2-substituents, and that the first and the fourth factor loadings multiplied by the corresponding standard deviation of the chemical shifts correlate with the CNDO/2 substituent-induced σ and π charge densities.