Chemical ionization mass spectra

The chemical potentials and free energies of the 2-isoxazolines have also been studied and the electron impact and chemical ionization mass spectra determined (77MI41614). Fragmentation pathways and retrocycloadditions of various derivatives were discussed in these reports. 

Chemical ionization mass spectra of the normal paraffins studied range from CsHis to the branched paraffins... 

For most of the experiments reported here the temperature of the ionization chamber was 150 °C., but to investigate the effect of temperature on chemical ionization mass spectra, runs were made at ionization chamber temperatures varying between 216° and 131 °C. 

Figure 1. Chemical ionization mass spectra of n-octadecane MW = 254, reactant — CHa, Pch4 = 1 torr...

In proceeding to a consideration of the chemical ionization mass spectra of more highly branched paraffins, it will be most convenient to consider separately the several different classes of alkyl ions found in the spectra—i.e., MW — 1+, MW — 15+, MW — 29 +, etc. We can see from Table II that a considerable amount of variation in the relative intensity of the MW — 1 ions (always the highest mass ion for which an intensity is given in the table) occurs. However, we shall show that the observed MW — 1 intensities can be approximately accounted for in terms of the concept of localized electrophilic attack by the reactant ion. First, however, we must consider the energetics of two processes which may be important in generating the spectra of branched paraffins. One of these is the abstraction of a primary hydrogen by the reactant ion. As a typical example we may write... 

The intensity of the MW — 43 ion in the chemical ionization mass spectra of normal paraffins in the Ci0-Ci2 range is about 0.04 of the total additive ionization. Considering the C9-C12 branched compounds listed in Table II, those compounds which can form the MW — 43 ion by a... 

The appearance and reproducibility of chemical ionization mass spectra depends on the ionizing conditions, principally the source temperature and presstire and the purity of the reagent gas. Chemical ionization mass spectra are generally not as reproducible as electron impact spectra. 

Chemical-ionization mass spectra of partially methylated aldono-nitrile acetates have been published.523 Intense peaks appear at M + 1 and M + 1 - 60, permitting determination of the number of substitutions. 

Transfer Chemical Ionization Mass Spectra of Isomeric C5 and Ce Alkanols. Can. J. Chem. 1981,59,2125-2132. 

Beckey, H.D. Comparison of Field lorrrzation and Chemical Ionization Mass Spectra of Decane Isomers. J. Am. Chem. Soc. 1966,88,5333-5335. 

Identification of compounds in the river water extracts was based on the coincidence of gas chromatographic retention times and on the equivalence of electron impact and chemical ionization mass spectra with those of authentic compounds. Quantitation was based on standard curves generated for selected compounds. 

FIGURE 11.33 Typical chemical ionization mass spectra taken using (a) HSCU as the chemical ionization reagent or (b) SiF5 as the Cl reagent. Note the change to a logarithmic scale in (b) above 2000 counts per second (CPS) (adapted from Mauldin et at., 1998 and Huey et al., 1998). 

The molecular ion regions of the chemical ionization mass spectra of 37 2 and 37 3 are listed in the table. Predict the expected intensities of M, M+1, and M+2 for each of the four species listed. Include contributions from C, H. O, and N, as appropriate. Compare your predictions with the observed values. Discrepant intensities in these data are typical unless care is taken to obtain high-quality data. 

The NMR spectra were obtained at either 300 or 600 MHz for protons and 75.5 or 150.9 MHz for carbon CDC13 was the solvent unless otherwise labeled. At 600 MHz, all 2-D spectra were obtained with gradients except INADEQUATE. The IR spectra were obtained neat (i.e. no solvent) unless otherwise labeled. The mass spectra were obtained by El GC-MS unless otherwise noted. Methane was used to obtain the chemical ionization mass spectra. 

Dougherty RC, Dalton J, Biros FJ (1972) Negative chemical ionization mass spectra of polycyclic chlorinated insecticides. Org Mass Spectrom 6 1171-1181... 

---