Electron impact fragmentation spectra

Similar experiments on a large number of transition metal carbonyls have shown that this process favors dissociation to and detection of metal clusters or atoms. Since most metal-(CO)n photofragments are themselves subject to efficient dissociation, MPI experiments do not identify the primary photoproducts. This situation contrasts sharply with electron impact ionization where the parent ion is usually formed and daughter ions are seen as a result of parent ion fragmentation. Figure 4 shows the electron impact mass spectrum of Mn2(C0) Q (33). for comparison with the MPI mass spectrum of Figure 3. 

A molecular ion is seen in the electron impact mass spectrum of compound (6) but the base peak is that resulting from the loss of nitrogen [M — 28] <91AG(E)1476>. The electron impact mass spectra of sydnones show the loss of NO and CO, either consecutively or simultaneously <84CHEC-I(6)365). A study of the Cl mass spectra of protonated sydnones, with methane as the reagent gas, shows that HNO and CO are the fragments lost <89H(29)185>. The electron impact mass spectrum of compound (19) shows an intense molecular ion which loses NO and then HCN <85JCS(Pi)2439>. 

The electron Impact Ionization spectrum of melphalan Is shown In Figure 6. It was obtained by direct-probe introduction of the sample on a Hewlett-Packard 5995A mass spectrometer (70 eV). The relative intensities of the most prominent fragments are given In Table III the abundance cut-off was 1Z. 

The electron impact mass spectrum of vitamin D3 obtained with a CEC Model 21-110B instrument (Consolidated Electrodynamics Corporation, Pasadena, CA) by direct probe sample introduction is shown in Figure 5 (22). It shows a strong molecular ion at m/z 384 and a fragmentation pattern characteristic of vitamins D2 and D3, their primary metabolites and other chemically related compounds. The fragment ion assignment is shown in Scheme III (22). 

Figure 3. Top. Ion/molecule reaction product formed by reaction of cis-dichloro-trans-dihydroxo-bis-2-propanamine platinum (IV) with its 50 eV electron impact fragments. Bottom. Dissociation pattern produced upon irradiation with cw CO2 laser, same experimental conditions and delay times as in the top spectrum. (Reproduced from ref. 18. Copyright 1987 American Chemical Society.)...

The electron impact mass spectrum of eugenol was measured using a Jeol JMS-DX 303 system. The spectrum is presented in Figure 6, and assignments for the main observed fragments are provided in Table 3. 

The electron impact (El) spectrum of nimodipine shown in Figure 13 was recorded using a Shimadzu PQ-5000 GC MS spectrometer. The spectrum shows a mass peak (M ) at = 418, and a base peak at m/z = 296 resulting from the loss of the nitrophenyl group. These and other proposed fragmentation patterns of the drug are presented in Table 5. 

The electron-impact mass spectrum of cleomiscosin A showed prominent fragment peaks at m/z 208 and 180, corresponding to ions E and F, which is explained in Fig. 9. 

The flash vacuum pyrolysis and the mass spectrometric fragmentation of a series of five methyl substituted phenanthrenes were correlated with each other in a quaUtatively predictable way.i ) The major thermochemical products for these compounds generally corresponded to one of the five most intense fragment ions in the compound s electron impact mass spectrum. The importance of products which corresponded to ions with high appearance potentials increased with increasing temperature in the thermolysis system. 

The thermal and mass spectral reactions of the dinitrobenzenes are even more interesting. ) The primary ionic and thermal decomposition reaction is in every case loss of NO2 to give a nitrophenyl cation or radical respectively. In both systems the nitrophenyl radicals may lose another NO2 fragment to give phenylene diradicals. In the case of o-dinitrobenzene loss of two NO2 fragments leads to the formation of benzjme. Benzofurazan, 44, is one of the minor products obtained from thermolysis of o-dinitro-benzene, it is also a minor ion in the electron impact mass spectrum of the compound. 

The electron impact ionization spectrum of sulfacetamide was obtained at 70 eV using a solid probe insertion and is shown in Figure 5. The spectrum was run on a Finnigan Mat 112S double focusing mass spectrometer connected to a PDP 11/34 (DEC) computer system. It shows a molecular ion peak M+ at m/z 214. Since the molecule contains one sulfur atom, M+2 peak appears at m/z 216. The proposed fragmentation pattern and prominent ions are given in Table IV. 

Peaks expected in the electron impact mass spectrum (as expected on the basis of fragmentation each side of every CO)... 

In the electron-impact mass spectrum of 12f, the molecular ion is observed at m/e 240,242 (M ), indicative of the presence of one bromine atom. Cyanic acid (m/e 42, base peak) is eliminated to give the prominent ion m/e 197, 199. Following elimination of SO2 (m/e 64) and on further impact, it either loses HBr to give the ion at m/e 54, or fragments to give BrCN and ethylene. A second pathway which has been observed also involves the initial loss of the bromine atom (80JHC977). 

Carbomethoxy-pedicularine (30) was proposed as the structure for an alkaloid of mass 235 amu from a NH3 chemical ionization gc/ms analysis of the alkaloid extract of the flowers of Penstemon whippleanus (Scrophula-riacaeae) (30). No molecular ion was observed in the electron impact mass spectrum, only an (M-45)+ ion at m/z 190. The further fragmentation of this ion (m/z 162,146, and 117) compared well with the mass spectrum of pedicularine (31) (1,82,83), so the alkaloid was tentatively suggested to be a carbomethoxypedicularine (30). Isomeric structures for this alkaloid cannot excluded, particularly given biogenetic considerations. The isolate may even be the methyl ester of pedicularine. 

Figure 2,32 An electron impact mass spectrum of aspirin (The following m/z fragments can be seen 43(C2H30 ), 92(CeH40 ), 120 (CyH402 ), 138 (CyHdO ), 180 (MH )).

The 70 eV electron Impact mass spectrum of acetohexamide, presented In Figure 10, was obtained on Varian MAT 311 mass spectrometer using Ion source pressure of 10 Torr, Ion source temperature of 180 C and an emission current of 300 pA. The molecular Ion Is detectable at m/e 324 and the base peak at m/e 56. A proposed fragmentation pattern and the mass/charge ratios of the major fragments are sham in Scheme 1. 

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