Electronic effects in the electron ionization fragmentations of 2‐aryl substituted octahydro‐1,3‐ and ‐3,1‐benzoxazines

Abstract

AbstractThe 70 eV electron ionization mass spectra of 27 2‐aryl substituted octahydro‐1,3‐ and ‐3,1‐benzoxazines have been recorded in order to find out how the site and stereochemistry of the ring fusion and especially the nature of the substitutent X on the 2‐phenyl group affect their fragmentation patterns. The structural isomers showed clearly different spectra; however, stereoisomeric differentiation was possible only with 1,3‐derivatives. The fragment‐ion peaks connected with the ionized ring and open chain forms of the compounds studied were clearly present 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 importance of different fragmentation channels varied according to the electron donating or withdrawing ability of the substituent X.