الفهرس 
Theoretical considerationsOnly 14 pages are availabe for public view
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Abstract
Abstract A mass spectrometer of the type QMS (SSQ710) is used to record the electron ionization mass spectra of some 6-fluoroquinolones molecules, namely: Norfloxacin, Pefloxacin, Ciprofloxacin and Levofloxacin.While the chemical ionization mass spectra of these compounds are recorded using Thermo Finnigan TRACE DSQ GC/MS system. In EI mass spectra, the relative intensities for the molecular ions [M• of the studied compounds and the prominent fragment ions are reported and discussed. Furthermore, fragmentation patterns for the four compounds have been suggested and discussed and the most important fragmentation processes such as [M-CO2]+•, [M-C2H4N]+ and [M-CO2-C2H4N]+are investigated. On the other hand, the chemical ionization (CI) mass spectra of the compounds have been recorded using methane as the reagent gas. These spectra are discussed in terms of the structure of the compounds, with particular reference to their conventional electron ionization mass spectra. The protonated molecules [M+H]+ are more relatively intense than [M]+• ions in the recorded EI mass spectra indicating higher stability in the case of [M+H]+. Also, fragmentation patterns for the four compounds have been suggested and discussed (using chemical ionization technique) and the most important fragmentation processes such as [MH-CO2]+•, [MH-C2H4N]+ and [MH-H2O]+ are investigated. Using MNDO semi-empirical method for computation together with the experimental results gave valuable information about the heats of formation and ionization energies of the molecules. The effect of substituents on the geometry of the neutral and ionized molecules are reflected in the values of the ionization energy and heats of formation of neutral Hf(M) and ionized ∆Hf(M)+∙ molecules. The calculated values for ionization energies of Norfloxacin, Pefloxacin, Ciprofloxacin and Levofloxacin are 8.1, 8, 8.8 and 8.3 eV, respectively. The calculated charge distributions at N1 and O12 in the qinolone ring of the studied molecules as well as the presence of a lone pair electrons at N1 and O12 atoms indicate that the ionization processes occur at these two atoms. The appearance (AE) and activation energies of the fragment ions [M-CO2]+• and [M-C2H4N]+ are also calculated and discussed. It is noteworthy that all the presently calculated values of ionization, appearance and activation energies are not yet published. The MNDO method is also used to probe the protonation of the studied compounds. The calculated proton affinities (PA’s) together with ∆Hf [M+H]+ values at nitrogen (N1) and at oxygen (O12) atoms are calculated. These results give interesting features for the protonation sites. The protonation at oxygen (O12) site is more favored than that at nitrogen (N1) site. Furthermore, the calculated values of the heats of formation of neutral [M], ionized [M]+•, protonated molecule [M+H]+ and PA’s values are reported for the first time.