No abstract

In the present communication we have measured ionization energies (ZE) for molecular ions M+' as well as appearance energies ( A E ) for [M-l]+ fragment ions at threshold produced from benzyl alcohol, benzyl amine and benzyl cyanide. The electron impact, ZE and A E data were obtained by using an Atlas CH-4 mass spectrometer and the data were treated using the deconvoluted first differential (DFD) technique.' Metastable peaks associated with the formation of [M -1]+ fragment ions were recorded-using an MM 16F mass spectrometer-at low electron energy (9-12 eV) in order to avoid interference from normal fragment ions. Kinetic energy release values ( were calculated2 from metastable peak width at half height. Molecular Ions. ZE and A E [M -1]+ values are presented in Table 1 together with K E released and AH, values calculated for [M -1]+ ions.

Appearance energies for [ C7H7]+ and [ C,H,I+ fragment ions obtained from methylphenol isomers were measured at the threshold using the electron impact technique. Different processes for the formation of the ions are suggested and discussed. Metastable peaks were detected and the kinetic energies released were determined. The results indicate that [ C7H,]+ ions are formed from methylphenols with both benzyl and tropylium structures, whereas [ C,H,]+ ions are formed with the phenyl structure at the detected thresholds. Kinetic energies released on fragmentation of reactive I C,H7]+ and I CHsl' ions were used as a probe for the structure of the ions at 70 eV.

An energetic study of the production of [C7H,N]+ and [C6H7]+ fragment ions from o-toluidine and Nmethylaniline is reported. The mechanisms for the formation of the ions are suggested. Metastable peaks associated with the formation and fragmentation of reactive [ C,H,N I + and I C6H7 1 .+ ions were detected and kinetic energy released were determined. The results indicate that the IC,H,N]+ ion is formed at threshold from o-toluidine with an aminotropylium structure whereas for N-methylaniline the ion is formed with an N-phenylmethaniminium structure. [ C,H,] + ions are believed to be formed at threshold from the two precursors with a protonated benzene structure.

The electron ionization mass spectra of 2-and 4-chlorodiphenylamine and 2-and 4-bromodiphenylamine are reported. All the spectra are characterized by strong molecular ion signals, corresponding to the base peak. Two primary fragmentations of significance include the expulsion of the substituents X and HX (X = halogen) from the four compounds. Further dissociation of the primary fragment ions results in the formation of some secondary decomposition ions having low or negligible relative abundances.

The relative intensity of the metastable peaks at 70 eV appearing at m/z 105.7 and 69.6 in the mass spectra of methylacetophenone isomers, as well as the kinetic energy (T,,,) released with the peaks at 14 and 70 eV respectively, are reported. The profile of all the metastable peaks studied has been found to be approximately Bat-topped. For the same transition it is found that the kinetic energy released with the metastable peaks formed by unimolecular decomposition of the three isomers decreases from the ortho to the para isomer. In addition, the kinetic energy released during the same transition is found to be roughly directly proportional to their corresponding intensity ratios. This result, together with the observation that the energy released with each metastable peak decreases by lowering the electron energy, may reveal the role of the internal energy of the reacting ions in producing the kinetic energy associated with the metastable peaks produced from methylacetophenone isomers.

The formation of a [CH,N]+ cation in the mass spectral fragmentation of amines is well known.' The ion exists in two stable forms; the well known enthalpy of the most stable [CH2NH2]' ion with methaniminium structure (a) is AH: 298 = 745 kJ mol-'.*S3 The methylnitrenium [CH,NH]+ ion (b) is the less stable structure with an uncertain AH: 2 9 8 value in the range of 866-11 17 kJ mol-'.4-6 Scheme 1 Scheme 2 Scheme 3 Scheme 4

An investigation employing the semiempirical molecular orbital MNDO method in the program package of the HyperChem 7.5 software to calculate ΔH f (M), ΔH f [M+H] + and local proton affinities (PAs) as well as the charge distributions for the two highly electronegative hetero atoms (O 11 and N 1) in six quinolone derivatives have been undertaken. The MNDO calculated values of PAs for the quinolone derivatives at site O 11 and at site N 1 indicate that the average energy separation between PA values at two respective sites is equal to about 164 kJ.mol-1. This allows the authors to conclude that the protonation at site O 11 is a more favoured process than at N 1. This conclusion can be explained as resulting from the presence of unsaturated carbonyl (C ═ O) double bond and ion pair electrons of the oxygen atom, which increase the influences of the protonation at O 11 site, which is known to be a good proton acceptor. The preferential protonation at site O 11 for the studied molecules have been confirmed by the calculated ΔH f [M+H] + values at sites O 11 and N 1 .