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 B²/E spectra as well as by collisional activation spectra of, for example, the ions m/z 82 and 67 from 7-azabicyclo4.2.0]octan-8-one and from cyclohexene. The only, and fairly weak, fragment ions including O and N are C₃H₃O]+, C_kH_2k-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]⁺˙.