Mass spectrometric studies

Charles C, Garcia P, Grolleau B and Turban G 1992 Mass spectrometric study of tetraethoxysilane and... 

Neon, a very inert element, is however said to form a compound with fluorine. It is still questionable if true compounds of neon exist, but evidence is mounting in favor of their existence. The ions, Ne+, (NeAr)+, (NeH)+, and (HeNe+) are known from optical and mass spectrometric studies. Neon also forms an unstable hydrate. 

More information has appeared concerning the nature of the side reactions, such as acetoxylation, which occur when certain methylated aromatic hydrocarbons are treated with mixtures prepared from nitric acid and acetic anhydride. Blackstock, Fischer, Richards, Vaughan and Wright have provided excellent evidence in support of a suggested ( 5.3.5) addition-elimination route towards 3,4-dimethylphenyl acetate in the reaction of o-xylene. Two intermediates were isolated, both of which gave rise to 3,4-dimethylphenyl acetate in aqueous acidic media and when subjected to vapour phase chromatography. One was positively identified, by ultraviolet, infra-red, n.m.r., and mass spectrometric studies, as the compound (l). The other was less stable and less well identified, but could be (ll). 

The first mass spectrometric study of thiazoles was carried out by Clark et al. (115), who investigated the method of fragmentation of thiazole, and 4-methyl- and 2,4-dimethylthiazole. 

Boron Monoxide and Dioxide. High temperature vapor phases of BO, B2O3, and BO2 have been the subject of a number of spectroscopic and mass spectrometric studies aimed at developiag theories of bonding, electronic stmctures, and thermochemical data (1,34). Values for the principal thermodynamic functions have been calculated and compiled for these gases (35). 

During the course of a mass spectrometric study of D-homo-14-hydroxy steroids, it was necessary to prepare the corresponding C-8 deuterium labeled analogs. The preparation of these uncommon steroid derivatives has been achieved by repeating the Torgov total synthesis [(257) (262)] with a deuterium-labeled bicyclic starting material (258). Both of the resulting 14-hydroxy epimers, (261) and (262), exhibited better than 90% isotopic purity. ... 

The author is grateful to Drs. P. Potter (AERE), D. W. Green (AML), J. K. Fink (ANL), and L. Leibowitz (ANL) for helpful discussions concerning the Pu-0 system. The author is particularly grateful to Dr. J. E. Battles (ANL) for providing this writer with his unpublished manuscript and permission to quote the results of a mass spectrometric study of the volatilization of plutonia. 

No evidence for PUO3 has been reported in mass spectrometric studies (31). However, the existence of the Pu + ion has been established by the observation of the hexafluoride (32). We have not included any Pu + in our calculations. 

Some of the problems encountered in the mass spectrometric study of ion-molecule reactions are illustrated in a review of the H2-He system (25). If the spectrometer ion source is used as a reaction chamber, a mixture of H2 and He are subjected to electron impact ionization, and both H2+ and He+ are potential reactant ions. The initial problem is iden-... 

Mass Spectrometric Study of Ions in Gases under Conventional Radiation Chemical Conditions... 

Mass spectrometric studies yield principally three types of information useful to the radiation chemist the major primary ions one should be concerned with, their reactions with neutral molecules, and thermodynamic information which allows one to eliminate certain reactions on the basis of endothermicity. In addition, attempts at theoretical interpretations of mass spectral fragmentation patterns permit estimates of unimolecular dissociation constants for excited parent ions. 

The first complication to be considered is the presence of an electrostatic field during the mass spectrometric study of the reaction. Only few quantitative studies have allowed for the possible contribution of hard collisions to cross-section (25), and the possibility that competitive reactions of the same ion may depend on ion energy is generally neglected in assigning ion-molecule reaction sequences. These effects, however, do not preclude qualitative application of mass spectrometric results to radiation chemistry. 

Mass Spectrometric Studies of Ion-Molecule Reactions in Gas Discharges... 

Mass spectrometric studies of the ionic species which arrive at the cathode of both glow and corona discharges yield useful information regarding ion-molecule reactions which occur within these systems. Glow discharges have been used to study endothermic reactions, and their usefulness and limitations have been demonstrated by studies of the dissociative charge transfer reactions Ar+ + N2 N+ + N + Ar N2+ + N2 N+ + N + N2 N2+ + 02 0+ + O + N2. Exo-... 

IR spectra have been reported for WSCI4 13, 57), and WSBr4 and WSCI3 (57). WSCI4 was also the subject of a mass-spectrometric study of the vaporization 359). The reaction of WSeCU with 1,2-dimethoxy-ethane has been investigated 56). 

Enzell, C.R., Francis, G.W., and Liaaen-Jensen, S., Mass spectrometric studies of carotenoids. 1. Occurrence and intensity ratios of M-92 and M-106 peaks, Acfa Chem. Scand., 22, 1054, 1968. 

Fukumura, H., Mibuka, N., Eura, S., Masuhara, H. and Nishi, N. (1993) Mass spectrometric studies on laser ablation of polystyrene sensitized with anthracene. J. Phys. Chem., 97, 13761-13766. 

A mass spectrometric study was carried out to establish tbe structure of compoimd 69. Its mass spectrum contains tbe molecular ion peak m/z 252 (16.98%) and a base peak (100%) at m/z 210, corresponding to 2-(2-hydroxypbenyl)benzimidazole (70). A tendency towards decreasing the heterocycle size is characteristic of the mass spectrometric behavior of 1,5-benzodiazepin-2-ones [61] and consequently the mass spectra of these compounds contains intense peaks of the corresponding benzimidazoles. It is also known that the mass spectrometric fragmentation of 1,5-benzodiazepines is similar to their thermal or acid decomposition. In fact, refluxing compound 69 in concentrated sulfuric acid yields benzimidazole 70 as the main product. 

Pastor E, Castro CM, Rodriguez JL, Gonzalez S. 1996. On-line mass spectrometric studies on the interaction between organic adlayers on platinum. Part 1. Consecutive adsorption of formic acid and propargyl alcohol. J Electroanal Chem 404 77-88. 

Mass spectrometric studies are not limited to the investigation of stable intermediates they have also been carried out on reaction transition states. The ultrafast studies by Zewail, for example, are nominally mass spectrometric based, where photoionization is used to detect reactive species on exceedingly short (femtosecond) time scales.Time resolved studies provide insight into the rates of unimo-lecular reactions, but do not provide direct thermochemical insight. 

The experiments with a beam of silver particles were conducted at room temperature. The energy of dissociation of diatomic molecules of silver is 1.78 eV, the heat of evaporation of silver molecules is 95 kcal/mol [46], and the heat of evaporation of an uniatomic silver is 64 kcal/mol. Mass-spectrometric studies [46] of silver vapour above a metallic silver showed that the ratio of number densities of ions Ag /Ag2 is equal to two. In other studies [47], a considerably larger value of this ratio was found. At 1037 - 1147 C molecular mass of silver particles in vapours was found to be 278 90 [46], i.e., an average number of atoms in a molecule of silver is 2.56. 

If the competition data are compared with electronegativity values for the halogens 85>, then tetrafluorobenzyne is clearly in an anomalous position. The only reasonable explanation available at present is that tetrafluorobenzyne is so destabilized by the inductive effect of the fluorine atoms that it has lost a considerable amount of the selectivity which arynes normally show. Estimates for the heats of formation of the isomeric dichlorobenzynes and for tetrachlorobenzyne have recently been made from mass spectrometric studies and these do indicate a low stability for tetrachlorobenzyne 86>. Evidently more data are required for the tetrahalogenobenzynes. 

Fig. 9. Pulse microreactor system for use with 13C-labeled hydrocarbons. D, E, and J are microreactors J contains the catalyst to be used for hydrocarbon skeletal reaction D and E are used, when necessary, to generate the required reactant hydrocarbon from a non-hydrocarbon precursor (e.g., alcohol dehydration in D and olefin hydrogenation in E) reactant injected at C. F is a trap which allows the accumulation of products from several reaction pulses before analysis G is a G.P.C. column, K a katharometer. Traps H collect fractions separated on G for subsequent mass spectrometric study. When generating reactant hydrocarbon in D and E, a two-step process is preferable in which, with J below reaction temperature, the purified reactant hydrocarbon is collected in H, and this is recycled as reactant with D and E below reaction temperature but with J at reaction temperature. After C. Corolleur, S. Corolleur, and F. G. Gault, J. Catal. 24, 385 (1972).

---