Rearrangement and predissociation processes in negative molecular ions of nitrobenzenes

The reactions of resonant electron capture by the molecules of benzene nitroderivatives has been studied in the gas phase. Some fragment negative ions were found to be unstable with respect to electron autodetachment. This circumstance has been used for the determination of their structure. In particular, it has been established that the low measured appearance energy of neutral component of [M? H]^? ion beam is a result of isomerization of nitrobenzenes' molecular ion, leading to the 2‐nitrosophenol structure with the subsequent formation of the phenoxide anion in the autodetaching state. The effective yield curves of some types of fragment ions demonstrate fine vibrational structures, testifying the predissociation mechanism of ion formation. For all detected ions, the absolute cross sections of formation have been measured. Copyright © 2009 John Wiley & Sons, Ltd.     

Infrared intensities of some SiH-containing compounds in the gas-phase

Infrared intensities measured in the gas-phase are reported for CH3SiH3, CH3SiD3, (CH3)2SiH2, (CH3)2SiD2, (SiH3)2CH2, (SiD3)2CH2, Si2H6, SiH2Cl2 and (SiH3)2O. These are compared with theoretical estimates from HF, MP2 and B3LYP calculations with the 6-311G** basis set. Literature values of nuCH intensities per bond from 18 compounds correlate linearly with the values calculated at MP2 and B3LYP levels: the corresponding HF plot is slightly curved. The new HC(Si) data fit these correlations adequately. In similar plots for SiH stretching intensity, the point for SiH2Cl2 is displaced, especially at the HF level. The lack of relation of nuCH or nuSiH intensity to Mulliken atomic charge points to the effect of varying atomic charge flux in the parameter thetamu/thetar. Anomalies associated with nuSiH intensities influenced by chlorine or OR substitution and previously explained by d(pi)-p(pi) bonding are attributed instead to charge flux variation. For silyl groups, deformation band intensities are roughly additive according to the number of such groups. However, this is not the case for the methyl symmetric deformation bands in methyl and dimethyl silanes.     

Microdetermination of carbon and hydrogen in organofluorine compounds

A simple method is described for the elimination of the interferences of fluorine in carbon and hydrogen determination of fluorinated organic compounds. Samples are burnt in a rapid flow of oxygen using the cobalto-cobaltic oxide, rapid straight empty tube, rapid empty tube of Belcher-Ingram, and flash combustion methods.The combustion products are passed through Anhydrone, silica gel-thorium nitrate, and soda asbestos absorption tubes, respectively. Carbon and hydrogen are determined gravimetrically. Acceptable results are generally obtained for a wide range of partially and highly fluorinated organic compounds.     

1,2,3,4-Tetrahydropyrimidines and some other compounds based on propiolic acid derivatives

The reactions of ethyl propiolate and propiolamide with methylene and benzaldehyde and anisaldehyde in an acidic medium, in which the corresponding 2-oxo-1,2,3,4-tetrahydropyrimidines and 1,4-dihydropyridines or a 3,4-dihydropyrimidine derivative are formed, were studied.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 4, pp. 529–531, April, 1984.     

Hidden rearrangement processes in short-lived negative molecular ions

The study of resonant electron capture by nitrobenzene molecules showed that some fragmentary negative ions are unstable toward electron autodetachment. The measured appearance energy of the neutral component of an [M — H]⁻ ion beam does not agree with the energetics of direct dissociation in a molecular ion. The estimation calculations show that the low appearance energy of [M — H]⁰ neutral components is caused by isomerization of a molecular ion of nitrobenzene to the 2-nitrobenzene structure followed by the formation of a phenoxide ion in the autodetachment state. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 367–370, February, 2006.     

Rearrangement processes in the mass spectra of some 3,5-dimethylisoxazole derivatives

The mass spectra of isoxazole and some 3,5-dimethylisoxazole derivatives were investigated. Schemes for the formation of the principal rearranged ions are proposed on the basis of a study of the dissociative ionization of labeled compounds. Examples of the effect of electronic and steric factors on the probability of the existence of different channels for disintegration of the molecular ion are presented. It is shown that the formation of an ion with mass 82 during the dissociative ionization of a number of the investigated compounds occurs via different mechanisms as a function of the nature of the substituents in the 4 position of the isoxazole ring.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 10, pp. 1336–1340, October, 1972.     

Detection of negative molecular ions in acrylic acid plasma: some implications for polymerization mechanisms

There is much scientific and commercial interest in plasma polymers to modify surface chemistry. To date, only neutral and positively charged species have been detected in the commonly applied acrylic acid plasma. Using time-averaged negative ion mass spectrometry, we demonstrate that large, negatively charged species exist in the plasma, contrary to previous studies that detected only neutral and positive species. We briefly outline how negative molecules may contribute to the deposition of plasma polymer in the acrylic acid system.     

The behaviour of stereoisomeric ions in the gas-phase. The case of some new macrocyclic ether-tetraesters

The electron impact mass spectrometric behaviour of some new diastereoisomeric macrocycles containing diglycolyl moiety as subcyclic unit is reported and discussed in detail with the aid of linked scans, exact mass measurements and collisionally activated decomposition mass analyzed ion kinetic energy spectra.     

Mass-spectrometric study of the cyclization of diazo compounds. 10. 2-Diazomalonic acid amides. Mass spectra of the negative ions

The mass spectra of the negative ions of the dissociative resonance capture of electrons of diazo amides and the isomeric triazoles were studied. The molecular negative ions of these compounds are unstable and do not undergo interisomerization. The principal fragmentation process involves the elimination of a molecule of nitrogen and transformation of the resulting [M-N₂]^– ions to the heterocyclic form, which is the same for the two isomers.See [1] for communication 9.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 7, pp. 941–944, July, 1987.     

Evidence for stepwise processes in the charge reversal of negative ions

Various processes during the charge reversal of the simple negative ions OH⁻, Cl^−·₂, CN⁻ and C₂H⁻ have been revealed by application of a voltage to the collision cell in the second field-free region of a VG Micromass ZAB-2F mass spectrometer. It is shown for all these ions that the two-electron stripping process required for charge reversal can take place not only in one step, but also in two steps. Moreover, for the Cl^−·₂ ions, it has been found that they can fragment to Cl⁻ ions prior to the two-electron stripping process. In the charge reversal of the OH⁻ and CN⁻ ions, some processes have been found which strongly indicate that even a one-step three-electron stripping is possible in addition to a stepwise process of two- and one-electron stripping. Many of the electron stripping processes are accompanied at some stage by fragmentation.     

Solvent extraction of uranium and some other metal ions with 2-N-butyl-2-ethyl octanohydroxamic acid

The solvent extraction of uranium by solutions of the new extractant 2-n-bytyl-2-ethyl octanohydroxamic acid (HX) in different solvents has been investigated as a function of pH, ligand and uranium concentrations. The results indicate that a 1 : 2 complex, UO₂X₂, is formed in solution, which has been confirmed by analysis of the isolated complex. Values of K_ext were 2.0, 6.6 × 10⁻³ and 1.3 × 10⁻³ in hexane, xylene and chloroform, respectively. Extraction behaviour of HX towards Zr, Ce, Ru, Sr and Cs has also been studied as a function of pH and the results are discussed.     

5,5,5-Trifluorolaevulic acid and some derived compounds

5,5,5-Trifluorolaevulic acid (II) has been prepared by the acidic hydrolysis of the Claisen condensation product (I) of ethyl trifluoroacetate and diethyl succinate. Dehydration of the acid (II) with phosphoric oxide gave 4-hydroxy-5,5,5-trifluoropent-3-enoic acid lactone (III). Reduction of either this lactone or the acid (II) with lithium aluminium hydride gave 5,5,5-trifluoropentane-1,4-diol (IV), from which 5,5,5-trifluoropenta-1,3-diene (VI) has been obtained by acetylation followed by pyrolysis.     

Mobilities of some positive and negative hydrogen ions in He and H2

Mobilities of H⁺ and H^? in He and in H₂, and of H⁺₂ and H⁺₃ in He, are calculated from ion-neutral potentials derived from theory and ion-beam scattering. Agreement with experiment is reasonable except for H^? in H₂ and H⁺₂ in He, which present unexplained puzzles.     

Thermal behaviour of malonic acid,sodium malonate and its compounds with some bivalent transition metal ions

Characterization, thermal stability and thermal decomposition of transition metal malonates, MCH₂C₂O₄·nH₂O (M = Mn(II), Fe(II), Co(II), Ni(II), Cu(II), Zn(II)), as well as, the thermal behaviour of malonic acid (C₃H₄O₄) and its sodium salt (Na₂CH₂C₂O₄·H₂O) were investigated employing simultaneous thermogravimetry and differential thermal analysis (TG-DTA), differential scanning calorimetry (DSC), infrared spectroscopy, TG-FTIR system, elemental analysis and complexometry. The dehydration, as well as, the thermal decomposition of the anhydrous compounds occurs in a single step. For the sodium malonate the final residue up to 700 °C is sodium carbonate, while the transition metal malonates the final residue up to 335 °C (Mn), 400 °C (Fe), 340 °C (Co), 350 °C (Ni), 520 °C (Cu) and 450 °C (Zn) is Mn₃O₄, Fe₂O₃, Co₃O₄, NiO, CuO and ZnO, respectively. The results also provided information concerning the ligand's denticity, thermal behaviour and identification of some gaseous products evolved during the thermal decomposition of these compounds.     

Structural characterization of organic molecules by negative ions in laser microprobe mass spectrometry. Part 1—Neutral compounds

Laser microprobe mass spectrometry (LMMS) has been used to systematically study polyfunctional molecules, covering a wide range of structure and polarity. The knowledge about the mechanisms actually involved for desorption and ionization (DI) of organics by laser microbeam irradiation of solid samples at high-power density is rather limited. Therefore we have elaborated a set of tentative hypotheses about DI in LMMS, permitting consistent rationalization of detected signals. The technique apparently combines desorption under mild conditions, shown by the release of intact thermolabiles, with extensive fragmentation. Structural data are typically distributed between cations and anions. Interpretation of negative-ion detection mode mass spectra often represents intricate problems, partly due to the lack of sustaining background information from conventional mass spectrometry. Selected examples are presented to illustrate the occurrence of electron capture ionization, the role of heteroatoms in the formation of negative ions and the tendency to undergo complex skeletal rearrangements. Although LMMS was originally aimed at microprobe applications, it has been found to be a valuable tool in organic mass spectrometry.     

Fluorinated tropylium ions in the mass spectra of some polyfluoroaromatic compounds

The most prominent ion in the mass spectra of C₆F₅CH₂X (X ? H, Br, CH:CH₂, COCl, and CH₂C₆F₅) is C₇F₅H₂⁺, formulated as the pentafluorotropylium cation. This ion is also found, in an amount comparable to the parent ion, in the spectrum of (C₆F₅)₂CH₂. The heptafluorotropylium cation is found similarly in the spectrum of C₆F₅CF₃. The mass spectra of (C₆F₅)₂CHBr and [(C₆H₅)₂CH]₂ exhibit an ion C₁₃F₁₀H⁺ as the base peak, which is probably a pentafluorophenylpentafluorotropylium cation. The alcohol (C₆F₅)₂CHOH shows loss of C₆F₅, followed by 2H, as a major breakdown pathway. The mode of formation, and the subsequent fragmentation, of the major ions in these spectra, are discussed.     

The synthesis,spectroscopic and thermal study of oxamic acid compounds of some metal(II) ions

Summary The preparation of oxamic acid complexes of general formula M(H₂NCOCOO)₂·xH₂O (M = Mn^II, Co^II, Ni^II, Cu^II or Zn^II; x = 1 for Cu^II, x = 2 for the other metals) is reported. The i.r. and Raman spectra are discussed considering a trans-octahedral structure, formed by five-membered chelate rings with the amide oxygen and one carboxylic oxygen as donor atoms. The apical positions are occupied by water molecules. The thermal degradation process is very similar for the different complexes, first losing H₂O in one or different steps, then the fragments of the organic ligand to give the metal oxide as residue. The thermal degradation of the Cu^II and Zn^II compounds results in the formation of a new polymeric compound by deprotonation of the primary amide function in an endothermic process, the polymer further decomposes to form the metal oxide.