Epoxidation of 4,4-dimethyl-A-homo-4a-cholestene derivatives and a study of electron impact mass spectra of the epoxidation products

1982 ◽  
Vol 47 (1) ◽  
pp. 315-337 ◽  
Author(s):  
Helena Velgová ◽  
Antonín Trka
Keyword(s):  
Electron Impact ◽  
Mass Spectra ◽  
Molecular Ions ◽  
Mass Spectrometric ◽  
Characteristic Decomposition ◽  
Conformational Effects ◽  
Electron Impact Mass ◽  
Decomposition Pathway ◽  
Impact Mass

The effect of the substituent in the position 3 on the epoxidation of some 4,4-dimethyl-A-homo-4a-cholestene derivatives was investigated. The stereochemistry of the epoxidation is affected mainly by sterical and conformational effects. The mass spectrometric behaviour of epoxides IV-XI, XV-XX, XXIII and XXIV and of 4a,5-unsaturated 3-ketones XXI and XXVI was also studied. The double-transannular cleavage represents a common and characteristic decomposition pathway of molecular ions of these compounds.

Mass Spectra of Sodium N-Alkyl and N,N-Dialkyl Dithiocarbamates and Some Related Compounds

1976 ◽  
Vol 59 (3) ◽  
pp. 622-632 ◽  
Author(s):  
Francis I Onuska ◽  
Michael E Comba
Keyword(s):  
Electron Impact ◽  
Mass Spectra ◽  
Molecular Ions ◽  
Fragmentation Behavior ◽  
Zinc Salts ◽  
Electron Impact Mass ◽  
Related Compounds ◽  
Impact Mass

Abstract Electron impact mass spectra of 8 sodium alkyl and dialkyl dithiocarbamate salts are reported with the spectra of 2 dithiocarbamate zinc salts and N′,N′-dimetliyl-N,N-dimethylthiocarbamylsulfenamide. The investigated compounds all gave molecular ions, and generalized descriptions of their fragmentation behavior are presented.

Oxygen equilibration in the mass spectra of 2-benzoylbenzoic acid

1976 ◽  
Vol 29 (2) ◽  
pp. 301
Author(s):  
MJ Lacey ◽  
JS Shannon
Keyword(s):  
Mass Spectrum ◽  
Benzoic Acid ◽  
Electron Impact ◽  
Mass Spectra ◽  
Chemical Ionization ◽  
Molecular Ions ◽  
Electron Impact Mass Spectrum ◽  
Primary Fragmentation ◽  
Electron Impact Mass ◽  
Impact Mass

Positional integrity of the label is maintained in the molecular ions of 2-ben~oyl[18O]benzoic acid prior to a number of primary fragmentation modes. Positional integrity is also evident for some source and metastable reactions of the protonated molecular ions formed in its chemical ionization (H2) mass spectrum. The (M-Ph)+ ions formed in the electron impact mass spectrum, however, fragment further after complete equilibration of their oxygen atoms.

Field Desorption Mass Spectra of Polymer Chemicals

1978 ◽  
Vol 51 (5) ◽  
pp. 925-939 ◽  
Author(s):  
R. P. Lattimer ◽  
K. R. Welch
Keyword(s):  
Molecular Weight ◽  
Electron Impact ◽  
Mass Spectroscopy ◽  
Mass Spectra ◽  
Structural Data ◽  
Molecular Ions ◽  
Complex Mixtures ◽  
Electron Impact Mass ◽  
Impact Mass

Abstract From the results presented here, it is clear that FD-MS is a very effective analytical method for determining molecular weights of polymer chemicals. Molecular ions were the only prominent ions produced in the FD mode of analysis for the series of representative polymer chemicals discussed in this paper. Good molecular ion spectra were obtained even from compounds that are quite unstable, both structurally and thermally. It is also evident, on the other hand, that FD-MS by itself provides only limited chemical structure information. The molecular weight is provided and often nothing else. Fortunately the molecular weight and “chemical intuition” regarding the history of the sample in question are often enough to deduce the structure. If not, then other techniques are available to provide complementary information. Electron impact (EI) mass spectra can be run on the same samples to obtain fragmentation patterns, and other spectro-scopic techniques (infrared and magnetic resonance) can be used to provide detailed structural information. Several application areas can be identified in which FD-MS can play an important role in the characterization of nolymer chemicals in industry. These include chemical identification (molecular weight and structure determination), direct detection of components in mixtures, identification of liquid chromatographic (LC) effluents, characterization of polymer blooms and extracts, identification of vapors from polymer processing, and identification of polymer chemical degradation products. For many of these applications the samples to be analyzed are very complex mixtures of chemical compounds. Electron impact mass spectroscopy is quite limited in its ability to analyze such complex mixtures due to the extensive fragmentation (and perhaps decomposition) that takes place in the ion source. Since molecular ions are normally the only prominent ions formed in the FD mode of analysis, FD-MS can be a very powerful tool for the characterization of polymer chemical mixtures. In summary, field desorption mass spectroscopy can in many cases provide molecular weight and structural data for polymer chemicals heretofore not obtainable by any analytical technique. In addition this information complements well the structural data obtained by magnetic resonance, infrared, and electron impact mass spectroscopy. We therefore feel confident that FD-MS will become increasingly important in the characterization of polymer chemicals in the future.

Massenspektrometrische Untersuchungen an ungesättigten Kohlenwasserstoffen: Halogen-Wanderung bei Acetylenen und Olefinen / Mass Spectrometric Investigations on Unsaturated Hydrocarbons: Halogen Migration in the Molecular Ions of Acetylenes and Alkenes

1979 ◽  
Vol 34 (11) ◽  
pp. 1612-1614 ◽  
Author(s):  
Klaus K. Mayer ◽  
Ilona Matolović ◽  
Erich Fischer ◽  
Carl Djerassi
Keyword(s):  
Mass Spectrometry ◽  
High Resolution ◽  
Electron Impact ◽  
Molecular Ions ◽  
Mass Spectrometric ◽  
Electron Impact Mass Spectrometry ◽  
Unsaturated Hydrocarbons ◽  
Electron Impact Mass ◽  
Impact Mass

The migratory aptitude of halogens and simple nucleophilic substituents X in the molecular ions of alkynes 1-11 and alkenes 12-17 was investigated by electron-impact mass spectrometry using low and high resolution, metastable analysis and 2H-labelling.

Notizen: Fast Pulsed Laser Induced Electron Generation for Electron Impact Mass Spectrometry

1988 ◽  
Vol 43 (12) ◽  
pp. 1151-1153 ◽  
Author(s):  
E. R. Rohwer ◽  
R.C. Beavis ◽  
C. Köster ◽  
J. Lindner ◽  
J. Grotemeyer ◽  
...  
Keyword(s):  
Electron Impact ◽  
Mass Spectra ◽  
Ion Source ◽  
Electron Impact Mass Spectrometry ◽  
Uv Laser ◽  
Electron Generation ◽  
Medium Resolution ◽  
Electron Impact Mass ◽  
Impact Mass ◽  
Tof Ms

A new ultra fast electron impact (El) ion source is pre­sented that produces a very short, high intensity electron beam, allowing medium resolution mass spectra to be re­corded without pulsing the ion accelerating voltages in a time-of-flight mass spectrometer (TOF-MS). The ion source requires minimum modification of any TOF-MS equipped with an electrostatic ion reflector and UV-laser. El-spectra are presented for comparison with literature spectra.

Sign in / Sign up

Export Citation Format

Share Document