Search results for "ionization"

Direct pyrolysis in the mass spectrometer of aromatic polysulfonates and polythiosulfonates

1978

The thermal degradation mechanism of three aromatic polysulfonates and polythiosulfonates was investigated by direct pyrolysis in the ion source of a mass spectrometer. Thermal degradation reactions were followed directly by this method by detecting the thermal and electron impact induced fragments. The results obtained have provided evidence that sulfur dioxide extrusion from the polymer backbone takes place in these polymers above 300°C. The synthesis and molecular characterization of the polymers studied are reported in the text.

Strukturuntersuchung von polyestern durch direkten abbau im massenspektrometer, 1. Polyester der terephthalsäure

1976

Die Abbaureaktionen von Poly(athylenterephthalat) (1a), Poly(tetradeuteroathylenterephthalat) (1b), Poly(trimethylenterephthalat) (1c) und Poly(tetramethylenterephthalat) (1d) im Massenspektrometer wurden untersucht. Hierzu wurden die Polymeren direkt in der Ionenquelle des Massenspektrometers pyrolysiert und die entstehenden thermischen Bruchstucke durch Elektronenstos ionisiert und fragmentiert. Die thermisch- und elektronenstosinduzierten Abbaureaktionen lassen sich nebeneinander nachweisen. Die untersuchten polymeren Terephthalate 1a–d folgen in beiden Abbauschritten den gleichen Mechanismen und konnen anhand ihrer Pyrolyse-Massenspektren unterschieden werden. The degradation reactions …

Studies in organic mass spectrometry. IV. Electron impact induced fragmentation of 2-substituted 3-(5-isoxazolyl)-4(3H)-quinazolinones of pharmaceuti…

1984

The fragmentation under electron impact of thirteen 2-substituted-3-(5-isoxazolyl)-4(3H)-quinazolinones has been investigated with the aid of metastable ion detection and high resolution measurements. Molecular ions are always abundant and the main primary fragmentation route involves acetonitrile elimination through isoxazole ring opening. The other common processes, particularly those leading to the abundant [R-C8H4N2]+ ion (b or b'), as well as those due to the nature of the 2-substituent are reported and discussed.

ChemInform Abstract: Mass Spectrometry of 3,4-Dihydroquinazolin-4-ones of Pharmaceutical Interest. Part 3. Electron Ionization Mass Spectra of 2-Subs…

2010

The fragmentation reactions induced by electron impact of eighteen title compounds has been investigated with the aid of low beam energy spectra (14 eV, nom. value), metastable ion detection, high resolution measurements and labelling experiments. The loss of the 4-carbonyl oxygen together with the 3-substituent, which constitutes a characteristic fragmentation route of 3-aryl and 3-heteroaromatic substituted-4(3H)-quinazolinones, is again observed, but the presence of a carboxyethyl group at the 4′-position of the pyrazole ring is responsible of an anomalous loss of 47 daltons from the molecular ion. Lastly, a comparison with the previously described behaviour of 3-(5′-isoxazolyl) derivati…

Differentiation of isomeric cyclic diamides by electron impact mass spectra

1976

The behaviour under electron impact of two series of isomeric cyclopentane- and cyclohexane-1, 2- and -1, 3-dicarboxylic acid dipiperidides was studied. Diagnostic fragmentation pathways were found to differentiate the isomeric diamides. Additional evidence was obtained from the metastable transitions.

The effect of chlorine substituent(s) on the primary loss of a methyl radical from chlorinated veratroles (1,2-dimethoxybenzenes)

1989

Mass spectrometry of 3,4-dihydroquinazolin-4-ones of pharmaceutical interest. Part3. Electron ionization mass spectra of 2-substituted-3-(5′-pyrazoly…

1992

The fragmentation reactions induced by electron impact of eighteen title compounds has been investigated with the aid of low beam energy spectra (14 eV, nom. value), metastable ion detection, high resolution measurements and labelling experiments. The loss of the 4-carbonyl oxygen together with the 3-substituent, which constitutes a characteristic fragmentation route of 3-aryl and 3-heteroaromatic substituted-4(3H)-quinazolinones, is again observed, but the presence of a carboxyethyl group at the 4′-position of the pyrazole ring is responsible of an anomalous loss of 47 daltons from the molecular ion. Lastly, a comparison with the previously described behaviour of 3-(5′-isoxazolyl) derivati…

Über den thermischen abbau des poly(ɛ-caprolacton)s

1977

The thermal and electron impact induced degradation reactions of poly(e-caprolactone) {poly[oxy(1-oxohexamethylene)]} were investigated in a mass spectrometer. It can be shown that the favorated thermal degradation reaction is the cleavage of the ester bond and formation of ω-hydroxyl and ketene endgroups (Eq. (iii)) and with a lower intensity the cleavage of the OCH2-bond and formation of carboxyl-and pentenyl endgroups (Eq. (vii)). After electron impact and fragmentation of the pyrolysis products to carboxonium ions an elimination of caprolactone via a “zip”-mechanism can be observed (Eq. (v)).

Absolute cross-sections for the nonresonant multi-photon ionization of toluene and xylene in the gas phase

2001

Abstract The absolute multi-photon ionization cross-section of the phenyl ring was determined by laser-ionization of toluene and xylene molecules in the gas phase. Excitation was achieved using nonresonant four-photon absorption of the frequency doubled light of a 10 ns pulsed Nd:YAG laser (532 nm). The resulting ions were stored in a Penning trap and detected by time-of-flight mass spectrometry. The values of the cross-sections are 1.4(3)×10 −42 cm 8 W −4 s −1 and 1.3(3)×10 −42 cm 8 W −4 s −1 for toluene and xylene, respectively.

Mononuclear rearrangements of heterocycles in water/β-CD: information on the real site of reaction from structural modifications of substrates and fr…

2007

Abstract The effect of β-cyclodextrin (β-CD) on the reactivity in the base-catalyzed pathway for the rearrangement in water of some ( Z )-hydrazones of 3-benzoyl-1,2,4-oxadiazoles ( 1b – f ) into the relevant triazoles ( 2b – f ) was investigated, finding different behavior as a function of the proton concentration. ESIMS and 1 H NMR data evidence the formation of host – guest complexes. The whole of the experimental and calculated (MM2) data enabled us to draw some intriguing conclusions concerning the influence of the structures of the substrates and the nature of the formed host – guest complexes on the real site of the reaction.