ELECTRONIC EFFECTS IN THE ELECTRON IONIZATION FRAGMENTATIONS OF 2-ARYL SUBSTITUTED OCTAHYDRO-1,3-BENZOXAZINES AND OCTAHYDRO-3,1-BENZOXAZINES

The 70 eV electron ionization mass spectra of 27 2-aryl substituted oc tahydro-1,3- and -3,1-benzoxazines have been recorded in order to find out how the site and stereochemistry of the ring fusion and especiall y the nature of the substitutent X on the 2-phenyl group affect their fragmentation patterns. The structural isomers showed clearly differen t spectra; however, stereoisomeric differentiation was possible only w ith 1,3-derivatives. The fragment-ion peaks connected with the ionized ring and open chain forms of the compounds studied were clearly prese nt in all the spectra. Analogously to the results obtained in solution , the electron-withdrawing ability of X increased the abundance of the fragments originating from the ring form. Also, the relative importan ce of different fragmentation channels varied according to the electro n donating or withdrawing ability of the substituent X.