Kinetic Energy Release and Energy Partitioning During the Ionic Fragmentation in Metastable Ions

1983 ◽  
Vol 38 (5) ◽  
pp. 524-527
Author(s):  
F. H. Abd El-Kader ◽  
M. S. Abd El-Fattah
Keyword(s):  
Kinetic Energy ◽  
Temperature Dependence ◽  
Kinetic Energy Release ◽  
Molecular Ions ◽  
Energy Partitioning ◽  
Unimolecular Decomposition ◽  
Centrifugal Barrier ◽  
Metastable Ions ◽  
Significant Temperature ◽  
Ionic Fragmentation

The kinetic energy released in the unimolecular decomposition of some metastable transitions has been investigated. It was found to have a significant temperature dependence in cases of H‘ loss from molecular ions. This is attributed to the tunelling of H• atom through the centrifugal barrier.The activation energies of the reverse reactions “εr≠” and the kinetic energy released “TB” have been determined for the loss of H• from acetonitrile and elimination of HCN from benzonitrile. The partitioning energy quotients q=TB/εr≠ are found = 0.91 and 0.58 for acetonitrile and benzonitrile respectively.

Kinetic Energy Release and Position of the Transition State for С6Н7+ Ions Produced from Isomeric C7H8O Precursors

1991 ◽  
Vol 46 (12) ◽  
pp. 1021-1025 ◽  
Author(s):  
Ezzat T. M. Selim ◽  
M. A. Rabbih ◽  
M. A. Fahmey
Keyword(s):  
Kinetic Energy ◽  
Transition State ◽  
Energy Release ◽  
Benzyl Alcohol ◽  
Kinetic Energy Release ◽  
Heat Of Formation ◽  
Molecular Ions ◽  
Energy Partitioning ◽  
Endothermic Reaction ◽  
Late Transition

Abstract The energetic requirement and mechanisms for CHO' loss from the molecular ions of isomeric C7H8O precursors have been reported. The heat of formation of [C6H7]+ (protonated benzene) was determined and ε* evaluated. Measurement of the kinetic energy release TB gives the energy-partitioning quotients q= TB/εr* which range from 0.38 to 0.99. The energy available and TB are small for the strongly endothermic reaction of benzyl alcohol but increase sharply in the case of the weakly endothermic reaction of anisole. All reactions have "late" transition states, the position X0*of the transition state on the reaction coordinate varying from 0.64 to 0.93

Metastable Ions as a Guide to Reaction Mechanisms. Loss of ’OH from Substituted Nitrobenzene Molecular Ions

1974 ◽  
Vol 29 (3) ◽  
pp. 507-512
Author(s):  
T. Keough ◽  
J. H. Beynon ◽  
R. G. Cooks ◽  
C. Chang ◽  
R. H. Shapiro
Keyword(s):  
Nitro Group ◽  
Hydrogen Transfer ◽  
Direct Interaction ◽  
Kinetic Energy Release ◽  
Molecular Ions ◽  
Time Range ◽  
Direct Role ◽  
Ion Fragmentation ◽  
Distinct Process ◽  
Metastable Ions

Loss of ‘OH from the molecular ions of nitrobenzenes having various substituents in the m- and p-positions does not involve substituent randomization and reaction through the ortho-isomer; the kinetic energy release accompanying metastable ion fragmentation shows this latter to be an entirely distinct process. The origin of the hydrogen lost as 'OH in the m- and p-compounds is the ring (mainly the position ortho to the nitro group in methyl p-nitrobenzoate). However, the hydro­gens of the substituent do play a direct role in the reaction as shown by an isotope effect upon the abundances of metastable peaks. Hydrogen atom abstraction by the ionized nitro group apparently occurs independently of participation by the substituent on the nitrobenzene but a second hydrogen transfer from this substituent to the ring precedes fragmentation. Direct interaction between groups o ' the aromatic ring that are not ortho to each other therefore apparently does not occur. Inversion of the rate constants for two reactions, NO' loss and CH2O loss from the methyl p-nitrobenzoate molecular ion in the metastable ion time range, has been observed following isotopic substitution.

Kinetic energy release and mean life time of metastable ions produced from C3H3N

Vacuum ◽  
2009 ◽  
Vol 83 ◽  
pp. S20-S23 ◽  
Author(s):  
K. Głuch ◽  
E. Szot ◽  
A. Gruszecka ◽  
M. Szymańska-Chargot ◽  
J. Cytawa ◽  
...  
Keyword(s):  
Kinetic Energy ◽  
Energy Release ◽  
Life Time ◽  
Kinetic Energy Release ◽  
Metastable Ions

Massenspektrometrische Untersuchungen zur Genese von [M—Me] [M-Et] [C7H7]+ und [C7H8]+ aus n-Butyl- und n-Pentylbenzol: Zeitabhängige Nachbargruppeneffekte, Isomerisierungen und kompetitive Wasserstoff-Umlagerungen / Mass Spectrometric Investigations on the Formation of [M-Me] [M-Et] [C7H7]+ und [C7H8]+ from w-Butyl and w-Pentyl Benzenes: Time Dependent Neighbouring Group Participation, Isomerization and Competitive Hydrogen Rearrangements

1978 ◽  
Vol 33 (10) ◽  
pp. 1150-1164 ◽  
Author(s):  
Chrysostomos Wesdemiotis ◽  
Helmut Schwarz ◽  
Friedrich Borchers ◽  
Heinz Heimbach ◽  
Karsten Levsen ◽  
...  
Keyword(s):  
Hydrogen Exchange ◽  
Hydrogen Transfer ◽  
High Resolution Mass Spectrometry ◽  
Kinetic Energy Release ◽  
Molecular Ions ◽  
Mass Spectrometric ◽  
Time Dependent ◽  
Alkyl Chains ◽  
Neighbouring Group Participation ◽  
Metastable Ions

Abstract The details of the elimination of CH3· and C2H5· from the molecular ions of n-butyl and n-pentyl benzenes as well as the formation of C7H7+ and C7H7+ -have been established using a combination of different mass spectrometric techniques. Among these techniques are field ionization kinetics (FIK), collisional activation (CA), unimolecular decomposi-tion of metastable ions (MI), kinetic energy release determinations (Tkin)> appearance potential measurements (AP) as well as high resolution mass spectrometry. The appli-cation of these methods and the investigation of nine 13 carbon and eleven deuterium labelled n-butyl and n-pentyl benzenes clearly demonstrate that 1) the loss of methyl and ethyl from terminal positions of the alkyl chains are accompanied by an interaction with the phenyl ring and 2) the regioselectivity of these processes is time dependent. Contrary to previous conclusions it is shown that hydrogen transfer in the formation of C7H8+ -occurs via five-, six-and seven-membered transition states. The time dependence of the hydrogen exchange reaction preceding the alkene eliminations is discussed in detail.

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).

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