The mass spectra of pyrimidines. II. 2(1H)-Pyrimidinethiones and some N(1)-substituted derivatives

1984 ◽  
Vol 62 (11) ◽  
pp. 2340-2343 ◽  
Author(s):  
Robin T. B. Rye ◽  
Oswald S. Tee ◽  
Eva M. Kazdan
Keyword(s):  
Kinetic Energy ◽  
Energy Release ◽  
Mass Spectra ◽  
Kinetic Energy Release ◽  
Exact Mass ◽  
Metastable Peak ◽  
Fragmentation Pathways

The EI induced fragmentation of 2(1H)-pyrimidinethione (1), some N(1)-substituted derivatives, and 2(1H)-pyrimidineselenone (4) have been studied. Principal fragmentation pathways have been identified using 2H-labelling, metastable defocussing, and exact mass measurements.The fragmentations of 1 and 4 generally parallel those reported for 2(1H)-pyrimidinone. In contrast to the oxo-compound, however, direct expulsion of the exocyclic hetero atom is significant in the fragmentation of 1, and dominates the spectrum of 4.Based on metastable peak abundances and kinetic energy release measurements, it is postulated that the [M – H]+ entity generated from N-ethyl-2-pyrimidinethione has a thiazolinium structure.

scholarly journals Ringöffnung CO+- und COOCH3+·-substituierter Cyclopropane und CO-Eliminierung aus isomeren C3H5CO+-Ionen / Ring Opening of CO+ and COOCH3+· Substituted Cyclopropanes and CO Loss from Isomeric C3H5CO+ Ions

1979 ◽  
Vol 34 (3) ◽  
pp. 488-494 ◽  
Author(s):  
Helmut Schwarz ◽  
Chrysostomos Wesdemiotis
Keyword(s):  
Kinetic Energy ◽  
Energy Release ◽  
Ring Opening ◽  
Collisional Activation ◽  
Kinetic Energy Release ◽  
Ester Group ◽  
Molecular Ions ◽  
Peak Shape ◽  
Metastable Peak ◽  
Substituted Cyclopropanes

Abstract The non-decomposing molecular ions of methyl cyclopropanecarboxylate (14) are found to rearrange to ionised methyl but-3-enoate (15). For ions with sufficient internal energy to decompose, this isomerization is in competition with · OCH3 loss, via direct cleavage of the ester group. Collisional activation spectroscopy may be used to distinguish between the C3H5CO+ ions formed by · OCH3 loss from the molecular ions of 14, 15 and other isomeric precursors. Four distinct C3H5CO+ species (18-21) can be identified in this way; these C3H5CO+ ions may themselves decompose, via CO elimination. Consideration of the metastable peak shape for CO loss, in conjunction with collisional activation spectroscopy on the resulting C3H5+ -ions, leads to two main conclusions, (i) Two C3H5+ ions (22 and 27) exist in potential energy wells. The very narrow metastable peaks for CO loss from 19 and 21 (leading to 22 and 27, respectively) show that these processes are continuously endothermic. In contrast, CO loss from either 18 or 20 gives rise to much broader metastable peaks. This suggests that rate-determining rearrangement of the incipient C3H5+ cations, to a more stable isomer, occurs prior to decomposition, (ii) Elimination of CO from the [M- · OCH3]+ fragment of 14 gives rise to a composite metastable peak, thus indicating the occurrence of two competing channels for dissociation. These channels are assigned to CO loss from 18 (larger kinetic energy release) and CO loss from 19 (smaller kinetic energy release).

The structure and fragmentation of protonated carboxylic acids in the gas phase

1979 ◽  
Vol 57 (21) ◽  
pp. 2827-2833 ◽  
Author(s):  
Nora E. Middlemiss ◽  
Alex. G. Harrison
Keyword(s):  
Kinetic Energy ◽  
Energy Release ◽  
Gas Phase ◽  
Activation Barrier ◽  
Kinetic Energy Release ◽  
Drift Region ◽  
Metastable Peak ◽  
Butyl Esters ◽  
Peak Intensity ◽  
A Minor

Gaseous protonated acids fragment in the first drift region of a double focussing mass spectrometer to yield the corresponding acylium ion and water. The metastable peaks for this fragmentation reaction have been recorded for the protonated acids from acetic to valeric and the kinetic energy release distributions evaluated from the metastable peak shapes. The protonated acids were produced by dissociative ionization of the ethyl, propyl, and butyl esters. The results provide evidence for two structures for gaseous protonated acids. Fragmentation of the hydroxyl protonated structure, a minor contributor to the metastable peak intensity, shows a low kinetic energy release (T(most probable) = 0.02 eV) as would be expected for a simple bond fission reaction. Fragmentation of the carbonyl protonated acid, which represents the major part of the metastable peak, is accompanied by a muchlarger kinetic energy release (T(most probable) = 0.30 to 0.43 eV). This result is interpreted in terms of an activation barrier for fragmentation of the carbonyl protonated acid which is considerably greater than the reaction endothermicity, with the excess energy being partitioned between internal energy and kinetic energy of the fragments. The results indicate that the addition of the acylium ion to water in the gas phase to produce the carbonyl protonated acid has an activation energy barrier.

Kinetic energy distributions from the shapes of metastable peaks

1974 ◽  
Vol 341 (1625) ◽  
pp. 135-146 ◽  
Keyword(s):  
Kinetic Energy ◽  
Energy Release ◽  
Kinetic Energy Release ◽  
Average Kinetic Energy ◽  
Translational Energy ◽  
Energy Distributions ◽  
Metastable Peak ◽  
Average Value ◽  
Half Height ◽  
Kinetic Energy Distributions

A general procedure is presented for determining the distribution of translational energies released in unimolecular ionic reactions occurring in the analyser of a mass spectrometer. It is shown that the method is applicable to reactions in which the average kinetic energy release covers a wide range (< 1 meV to ca . 3 eV). The treatment avoids making approximations either in the calculation of metastable peak shapes or in the subsequent determination of the translational energy distribution. Excellent agreement is achieved between experimental and calculated metastable peak shapes and the kinetic energy distributions represent the first accurate values obtained by a generally applicable technique. The relation between the average kinetic energy released and the width at half height of the corresponding metastable peak has been explored for peaks of various shapes. For gaussian-type peaks the kinetic energy release calculated from the half height is smaller by a factor of two to three than the average value, while for dish topped peaks it approximately equals the average value.

Isotope effects on kinetic energy release. Elimination of CH4 from [CH3CHOH]+ and [CH2OCH3]+

1989 ◽  
Vol 93 (2) ◽  
pp. 215-223 ◽  
Author(s):  
Kevin F. Donchi ◽  
Einar Uggerud ◽  
Georg Hvistendahl ◽  
Peter J. Derrick
Keyword(s):  
Kinetic Energy ◽  
Energy Release ◽  
Isotope Effects ◽  
Kinetic Energy Release
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