GC-MS and IR studies on the six ring regioisomeric dimethoxybenzoyl-N-methylpiperazines (DMBzMPs)

The complete series of regioisomeric dimethoxybenzoyl-N-methylpiperazines were synthesized and evaluated in GC-MS and FTIR studies. The EI mass spectra show fragment ions characteristic of both the dimethoxybenzoyl and the N-methylpiperazine portions of the molecules. These characteristic fragments include the dimethoxybenzoyl cation at m/z 165 as well as the m/z 99 N-methylpiperazine cation and the low mass cation species at m/z 56 (C3H6 N(+)) and the m/z 70 ion (C4H8N(+)). Unique radical cations characteristic for the benzoyl-N-methylpiperazines were observed at m/z 83 (C5H9 N(+)) and m/z 207 (C11H13NO3(+)) Deuterium labeling experiments were used to characterize the mechanism of formation of these fragment ions. Attenuated total reflection infrared spectroscopy provides direct confirmatory data for the differentiation between the six regioisomeric aromatic ring substituted dimethoxybenzoyl-N-methylpiperazines. Gas chromatographic separation of this series of compounds was accomplished on an Rtx-200 stationary phase and relative retention appears related to the degree of steric crowding of the aromatic ring substituents. The most crowded patterns of substitution elute first while the more symmetrical 1-, 3-, 5-substitution pattern has the highest retention time.