Mndo study of fragmentations in mass spectrometry. Part II. Substituent effects in the ioinization of [CH3?CO?R] compounds and their enol tautomers

A semiempirical MNDO method was used in calculations on monosubstituted neutral and cationic compounds of the CH₃? CO? R] type with a wide range of substituents (R = H, F, Cl, CH₃, NH₂, OH, OCH₃, NHCH₃, CH?CH₂). The results obtained are interpreted with respect to the effect of the individual substituents on the geometry and electron distribution in the systems studied and allow the conclusion that the ratios of partial charges in the individual substructures in a radical cation correspond to those of the respective peak intensities in the mass spectrum.