MNDO study of fragmentations in mass spectrometry. Part I. The geometry and electron structure of [C3H6O] + ˙ systems and [C2H3O]+ ions

MNDO calculations of [C3H6O]+ ˙ predict the parallel existence of both structures of radical cations of acetone (1) and propen‐2‐ol (2) in electron ionization spectra. The calculated heats of formation of 1+ ˙ (ΔHfMNDO = 783.2 kj mol−1) and of 2+ ˙ (ΔHfMNDO = 649.8 kJ mol−1) are in very good agreement with the experimental results. A comparison with the results of ab initio calculations (3–21 G and 6–31 G) and experimental data for the individual structures of the main fragment [C2H3O]+ demonstrates a sufficient accuracy of MNDO results, suggesting the possibility of applying the method also in other cationic systems, especially in larger ones.