Mass spectra of 1,2-alkylenedioxy-substituted and related benzofurazans and benzofuroxans: Differentiation between linear and angular isomers

The electron ionization (EI) mass spectra of [1,3]-dioxolo-, 6,7-dihydro-[1,4]-dioxino-, 7,8-dihydro-6H-[1,4]dioxepino-, 6,7,8,9-tetrahydro[1,4]dioxocino-, 7,8,9,10-tetrahydro-6H-[1,4]dioxonino- and 6,7,8,9,10,11-hexahydro[1,4]dioxerino[2,3-f]-2,1,3-benzoxadiazoles (benzofurazans) and the corresponding 1-oxides (benzofuroxans), all linear isomers, are reported. Also reported are the EI mass spectra of the corresponding angular isomers, [1,3]dioxolo-, 7,8-dihydro[1,4]dioxino-, 8,9-dihydro-7H-[1,4]dioxepino-, 7,8,9,10-tetrahydro[1,4]dioxocino-, 8,9,10,11-tetrahydro-7H-[1,4]dioxonino-, 7,8,9,10,11,12-hexahydro[1,4]dioxecino[2,3-e]-2,1,3-benzoxadiazoles and the corresponding 1-oxides. The relative abundance of the fragment ion of m/z 80 is characteristically enhanced in the spectra of the angular derivatives compared to the spectra of the linear counterparts. Collisionally activated decomposition studies show that it is structurally identical whether derived from the benzofurazans or the benzofuroxans. The relative abundance of the m/z 80 ion serves to distinguish between linear and angular isomeric pairs. In addition, the fragment ion at m/z 80 also serves to differentiate between the pairs of isomers, analogous to linear and angular, of six acyclic methoxy- and methoxymethyl-substituted benzofurazans and their corresponding benzofuroxans.