The Influence of the C-4′ Substituent on the Formation of Benzoyl Ions during Electron Ionization-Induced Decomposition of Some 2-Phenyl-1,3,4-Oxadiazoles

2002 ◽  
Vol 8 (4) ◽  
pp. 295-298 ◽  
Author(s):  
Rafał Frahski ◽  
Krystian Eitner ◽  
Grzegorz Schroeder ◽  
Volodymir Rybachenko
Keyword(s):  
Charge Density ◽  
Phenyl Ring ◽  
Molecular Ions ◽  
Electron Ionization ◽  
Ion Current ◽  
Fragment Ions ◽  
Induced Decomposition ◽  
Linear Correlations ◽  
Positively Charged

The effect of the C-4′ substituent for the formation of benzoyl ions during electron ionization-induced decomposition of some 2-phenyl-1,3,4-oxadiazoles is studied. The formation of these ions occurs via an azirane ion. The sums of the abundances of benzoyl ions and abundances of fragment ions derived from them, expressed as a percentage of total-ion current, were compared with the calculated charge density on both C-4′ atoms and atoms connected with C-4′ atoms. Linear correlations were found for both molecular and intermediate azirane ions. In the case of substituents which are less likely to be positively charged, the peaks of benzoyl ions have higher relative intensities. It is deduced that ionization in the phenyl ring strongly affects the formation of benzoyl ions from molecular ions of the studied compounds.

Unimolecular Gas-Phase Reactions of Diethyl Phthalate, Isophthalate, and Terephthalate upon Electron Ionization

2003 ◽  
Vol 56 (5) ◽  
pp. 473 ◽  
Author(s):  
Susumu Tajima ◽  
Masashi Mamada ◽  
Satoshi Nakajima ◽  
Yutaka Takahashi ◽  
Nico M. M. Nibbering
Keyword(s):  
Gas Phase ◽  
Molecular Ions ◽  
Ion Source ◽  
Electron Ionization ◽  
Diethyl Phthalate ◽  
Gas Phase Reactions ◽  
Fragment Ions ◽  
Metastable Fragmentation ◽  
Primary Fragmentation ◽  
Ion Kinetic Energy

Unimolecular gas-phase reactions of diethyl phthalate (1), isophthalate (2), and terephthalate (3), upon electron ionization, have been investigated by use of mass-analyzed ion kinetic energy (MIKE) spectrometry and deuterium labelling. The metastable molecular ions (1)+ decompose to give exclusively the ions m/z 176 ([M – CH3CH2OH]+) and not the ions by the loss of CH3CH2O as proposed earlier in the literature. The metastable molecular ions (2)+ and (3)+ fragment differently from (1)+ and lead not only to the formation of the major fragment ions m/z 194 ([M − CH2CH2]+) via a McLafferty rearrangement but also to minor fragment ions m/z 193 ([M – CH2CH3]+).Yet, molecular ions decomposing in the ion source all show as primary fragmentation channel the loss of CH3CH2O to give the ions at m/z 177, which further dissociate to give the ions at m/z 149 through the loss of C2H4 or CO, indicating the resulting ions are +COC6H4COOH and +C6H4COOCH2CH3. The +COC6H4COOH ions decompose into the m/z 121, 93, and 65 ions by the consecutive losses of three carbon monoxide molecules, respectively. Prior to the second CO loss, a migration of the OH group to the benzene ring occurs. During the metastable fragmentation of the +C6H4COOCH2CH3 ions no ethoxy migration occurs, in contrast to the methoxy migration taking place in the metastable decomposition of the lower homologue +C6H4COOCH3 ions.

Structural Characterization and Differentiation of Isomeric ω-Bromoalkoxy Derivatives of (E)-Chalcone by Means of Mass Spectrometry

2008 ◽  
Vol 14 (1) ◽  
pp. 37-47 ◽  
Author(s):  
Zdzisława Nowakowska
Keyword(s):  
Mass Spectrometry ◽  
Electrospray Ionization ◽  
Structural Characterization ◽  
Molecular Ions ◽  
Electron Ionization ◽  
Cone Voltage ◽  
Fragment Ions ◽  
The Difference ◽  
Derivatives Of

Mass spectrometry with electron ionization and electrospray ionization have been applied to characterize and differentiate the isomeric ortho-, meta- or para-( E)-bromoalkyloxychalcones 1–15. The difference in the values of μ1–μ5 (i.e. the ratio of abundances of the selected fragment ions to those of the molecular ions) in the series of isomeric chalcones studied and the so-called “in-source” fragmentation induced by increasing cone voltage have been found to be important and reliable indicators differentiating the isomers studied.

Die kinetische Energie ionisierter Molekülfragmente I. Methodik

1964 ◽  
Vol 19 (4) ◽  
pp. 484-493 ◽  
Author(s):  
Rolf Taubert
Keyword(s):  
Probability Function ◽  
Solid Angle ◽  
Initial Energy ◽  
Ion Source ◽  
Distribution Functions ◽  
Velocity Space ◽  
Ion Current ◽  
Molecular Fragments ◽  
Fragment Ions ◽  
Energy Distribution Functions

Methods of measuring initial energies of ionized molecular fragments are discussed in terms of the velocity space. An ion source together with the collector arrangement define a certain part of the velocity space from where ions are collected. If this part is not equivalent to a fixed solid angle in velocity space, discrimination due to initial energy takes place. Well defined discrimination effects can be used to measure the initial energy probability function WE of an ion ensemble. Emphasis is laid especially upon the deflection method. Using this method one obtaines the probability function WE simply by differentiating the primarily measured ion current distribution. The necessary working conditions which have to be fulfilled are discussed in some detail and an experimental arrangement is described, which has been used to measure the initial energy distribution functions of fragment ions from the lower paraffins.

scholarly journals Charge Density Studies on Anti-Alzheimer Agents

2014 ◽  
Vol 70 (a1) ◽  
pp. C969-C969
Author(s):  
Peter Luger ◽  
Stefan Mebs ◽  
Manuela Weber ◽  
Birger Dittrich
Keyword(s):  
Methylene Blue ◽  
Charge Density ◽  
Tau Protein ◽  
Positive Charge ◽  
Brain Disorders ◽  
Electronic Interactions ◽  
Hirshfeld Surfaces ◽  
Spherical Structures ◽  
The Brain ◽  
Positively Charged

The average age of people is increasing continuously thanks to the progress in the medicinal sciences and further social advances. As a consequence, however, diseases which affect people more likely at a higher age also increase. In this course Alzheimer's disease (AD) and related brain disorders distribute rapidly and have to be taken more serious. One of the most frequently applied drugs against AD is donepezil®. Its function is a reversible inhibition of acetylcholinesterase (AChE), thereby reducing the deficit of acetylcholine associated with the occurrence of AD. As one result from the charge density (CD) of the small-molecule structure containing the donepezilium cation comparable electronic interactions were identified as in the macromolecular TcAChE-donepezil complex which were made visible by electrostatic potential and Hirshfeld surfaces.[1] Two newer developments of Alzheimer agents are bexarotene and methylene blue. For the first one a therapeutic effect on AD in a mouse model was recently reported. From a comparative CD study on bexarotene and its disila analogue differences in the electrostatic potentials were identified, while the spherical structures showed no significant differences. The second one, methylene blue, targets the abnormal tangle type tau protein aggregation inside the nerve cells in the brain and stops its spread. The molecule is positively charged with various counterions. From the CD an answer to the not yet understood question is expected whether the formal positive charge is localized or delocalized.

Continuous flow fast atom bombardment mass spectrometry of mononucleotides and their metal complexes

1989 ◽  
Vol 67 (5) ◽  
pp. 910-920 ◽  
Author(s):  
M. J. Bertrand ◽  
V. Benham ◽  
R. St-Louis ◽  
M. J. Evans
Keyword(s):  
Mass Spectrometry ◽  
Continuous Flow ◽  
Fast Atom Bombardment ◽  
Aqueous Media ◽  
Molecular Ions ◽  
Fragment Ions ◽  
Low Concentrations ◽  
Metal Adducts ◽  
Matrix Concentration

The mass spectra of mononucleotides and their metal adducts Na, K, Mg, Ca, Ni, Co, Cu, and Zn of guanosine 5′-monophosphate (5′-GMP) as well as H, Na, and Mg of adenosine 5′-monophosphate (5′-AMP) and H and Ni of inosine 5′-monophosphate (5′-IMP) have been obtained in low concentrations of matrix in water using continuous-flow fast atom bombardment. The results indicate that this technique is suitable for the analysis of these complexes in aqueous media and yields spectra that are highly characteristic of the compounds analyzed. Parent-molecular ions and structurally significant fragment ions are observed for all compounds studied and the different binding sites for the metal on the nucleotides can be isolated from the fragment ions. Experimental parameters influencing the quality of the spectra such as flow rate, matrix concentration, matrix nature, and analyte concentration have been studied and optimized. For the thirteen compounds studied, it appears that continuous-flow FAB is superior to conventional FAB and that good quality spectra can be obtained with as little as 0.5% of added matrix thus minimizing spectral interferences. Keywords: continuous flow FAB, FAB MS, mass spectrometry, nucleotides, metal-nucleotides.

Rearrangements in the Molecular Ions of Some ortho-Substituted Schiff Bases

1993 ◽  
Vol 46 (6) ◽  
pp. 895 ◽  
Author(s):  
T Blumenthal ◽  
M Dosen ◽  
RG Gillis ◽  
QN Porter
Keyword(s):  
Kinetic Energy ◽  
Schiff Bases ◽  
Molecular Ions ◽  
Energy Spectra ◽  
Supporting Evidence ◽  
Deuterium Labelling ◽  
Methyl Group ◽  
Molecular Ion ◽  
Fragment Ions ◽  
Ion Kinetic Energy

Under electron ionization conditions, the ortho-substituted Schiff bases N-benzylidene-o-toluidine (1a), N-(o-methylbenzylidene)aniline (1b), N-salicylideneaniline (1c) and N-(o-methoxybenzylidene)aniline (1d) give fragment ions which have been shown by collision-activated mass-analysed ion kinetic energy spectra to have the structure of the protonated molecular ions of indole (2), benzofuran (3), and 1,2-benzisoxazole (4). The molecular ion of N-(o-methylbenzylidene)-o-toluidine (1f) gives as fragment ions not only the protonated molecular ion (2) of indole and the tropylium ion but also the molecular ion of anthracene. Attempts to find supporting evidence for a mechanism for this rearrangement by deuterium labelling of a methyl group in (1b), such as (1g), have been unsuccessful.

Mass spectral investigations on selenium compounds. II. The behaviour of meta-and para-substituted benzeneseleninic acids and of meta-nitrophenyl selenocyanate under electron impact

1982 ◽  
Vol 35 (7) ◽  
pp. 1365 ◽  
Author(s):  
A Benedetti ◽  
C Preti ◽  
L Tassi ◽  
G Tosi
Keyword(s):  
Mass Spectrometry ◽  
Mass Spectrum ◽  
Electron Impact ◽  
Molecular Ions ◽  
Selenium Compounds ◽  
Molecular Ion ◽  
Mass Spectral ◽  
Low Intensity ◽  
Fragment Ions

Substituted benzeneseleninic acids of the type XC6H4SeO2H (X = m-Cl, p-Cl, m-Br, p-Br, p-Me, m-NO2, p-NO2) have been investigated by mass spectrometry. The fragmentation modes and the fragment ions are discussed and compared with those obtained from the mass spectrum of m-nitro-phenyl selenocyanate, O2NC6H4SeCN. Generally, as regards the acids, besides very weak peaks due to the molecular ions, a number of peaks at higher mass numbers and of greater intensity is observed; these peaks are in multiplets typical of the presence of two selenium atoms, and they correspond to the disubstituted diphenyl diselenides of the type XC6H4SeSeC6H4X. m-Nitrophenyl selenocyanate shows an intense molecular ion peak and the relative fragmentation, while the peak due to the diselenide is of very low intensity.

Negative Ionen durch Elektronenstoß aus organischen Nitroverbindungen, Äthylnitrit und Äthylnitrat

1967 ◽  
Vol 22 (5) ◽  
pp. 700-704
Author(s):  
K. Jäger ◽  
A. Henglein
Keyword(s):  
Electron Impact ◽  
Negative Ions ◽  
Molecular Ions ◽  
Ion Source ◽  
Negative Ion ◽  
Electron Affinities ◽  
Low Intensity ◽  
Ion Molecule Reactions ◽  
Fragment Ions ◽  
Product Ions

Negative ion formation by electron impact has been studied in nitromethane, nitroethane, nitrobenzene, tetranitromethane, ethylnitrite and ethylnitrate. Appearance potentials, ionization efficiency curves and kinetic energies of negative ions were measured by using a Fox ion source. The electron affinities of C2H5O and of C (NO2)3 are discussed as well as the energetics of processes which yield NO2-. The electron capture in nitrobenzene and tetranitromethane leads to molecular ions [C6H5NO2~ in high, C (NO2)4 in very low intensity] besides many fragment ions. A number of product ions from negative ion-molecule reactions has also been found.

Nachweis metastabiler Ionen mit langen Lebensdauern

1965 ◽  
Vol 20 (12) ◽  
pp. 1708-1710 ◽  
Author(s):  
H. Tatarczyk ◽  
U. von Zahn
Keyword(s):  
Electron Impact ◽  
Drift Tube ◽  
Magnetic Spectrometer ◽  
Ion Current ◽  
Time Interval ◽  
Fragment Ions ◽  
Metastable Ions ◽  
Hydrocarbon Molecules

In order to search for metastable ions with long lifetimes hydrocarbon molecules are ionized by electron impact and the fragment ions preselected by a magnetic spectrometer. Subsequently these selected ions M0+ pass a drift tube where they may decay into ions M1+, Μ2+, .... Behind the drift tube a quadrupole spectrometer is used to analyze the ion current for its mass components M0+, M1+For selected species of fragment ions M0+ of n-butane, n-pentane, and n-hexane it was found that between 10% and 20% of M0+ decay in the time interval of 10 μs to 150 μs after ionization. Furthermore, 150 μs after ionization (0.040 ± 0.025) % of mass 86+ ions from n-hexane decompose into 56+ fragment ions per 1 μs.

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