Abstract: The investigation of the pathway of EIfragmentation of 4-chloro-4'-substituted benzyl butyl ketones with nine different ring substituents was accomplished by means of Mass-Analyzed Ion Kinetic Energy Spectra (MIKES). The results showed that the pathway was predominantly composed of Mclafferty Rearrangement of molecular ions followed by α-dissociation. Under lower impact electron energy down to 20eV, the α-disspciation leaction of product ions of Mclafferty Rearrangement could satisfactorily correspond with Hammeit eqtation resulting in the regression linear epuation lgZ/Z₀ =-0.378σ_p-0.008 with correlation coefficient 0.9949. The substituent effect of monofnolecular dissociation in mass spectrometry was obviously shown from present work.

Key words: 4-Chloro-4'-substituted benzyl ketone, Low energy election impact mass spectra, Substituent effect