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

Electron 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 B 2 / 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 [C 3 H 3 O]+, [C k H 2 k ‐2 N] + ( k = 5–8) and [C 3 H 6 N] + . 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 + NH 3 ] + ˙ and [2 M + 1] + ˙.