Electron impact and ammonia chemical ionization mass spectra of n‐azabicyclo[m.2.0]alkan‐(n + 1)‐ones (m = 3–6, n = 6–9)

Abstract

AbstractElectron impact induced fragmentation of the title compounds obeys a route where the lactam moiety, OCNH, is cleaved first, with the accompanying formation of a cycloalkene ion. This can be verified by low‐resolution, high‐resolution, B/E and B2/E spectra as well as by collisional activation spectra of, for example, the ions m/z 82 and 67 from 7‐azabicyclo[4.2.0]octan‐8‐one and from cyclohexene. The only, and fairly weak, fragment ions including O and N are [C3H3O]+, [CkH2k‐2N]+ (k = 5–8) and [C3H6N]+. The ammonia chemical ionization spectra are also characteristic for all four lactams and show the same dominant ions in all cases, namely [M + 1]+, [M + 1 + NH3]+˙ and [2 M + 1]+˙.