Metastable Ion Studies. V. The Identification of C2H4O+ · Ion Structures from their Characteristic Kinetic Energy Releases

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Ionic heats of formation and collisional activation (CA) mass spectra for fifteen isomeric or tautomeric [C4H4O]+• ions are described. Twelve of these species can be characterised by means of their CA mass spectra alone. The relative thermodynamic stabilities of keto–enol tautomers and the ease of interconversion of some ions are discussed. It is emphasised that CA spectra alone (i.e. in the absence of other information, such as heat of formation, etc.) may not easily be correlated with the appropriate ion structures.

“…Metastable peaks (33) and collisional activation mass spectra (18) were measured by conventional means.…”

Section: Trifluoroacetic-trans-crotonic Anhydride ( C F -C O G Co-cmentioning

confidence: 99%

Isomeric and tautomeric [C₄H₄O]^+• ions; their thermochemistry and collisionally induced fragmentation characteristics

Burgers¹,

Holmes²,

Lossing³

et al. 1982

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“…The production of (b) type ions may therefore be a minor process as is observed in the dissociation of the analogous C2H50+ ion (1).…”

Section: -mentioning

confidence: 99%

“…isopropanol, diethylether, etc.) (1). The behaviour of analogous nitrogen-containing compounds will be discussed below.…”

Section: Reference Ionsmentioning

confidence: 99%

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Metastable ion studies. VI. The identification of C₂H₅N^+• ion structures from their characteristic kinetic energy releases

Holmes¹,

Terlouw²

1976

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. Can. J. Chem. 54, 1007Chem. 54, (1976. Metastable peaks for the fragmentation C2H5N+. + C2HdN+ f H' have been studied in the first field-free region of a double focussing mass spectrometer. Isomeric structures of C2H5N+' ions derived from a variety of precursor molecules were characterised by their metastable peak shape and kinetic energy release. The identifications were aided by appropriate deuterium labelling experiments. Four isomeric ions (c) (e) were shown to retain their structural identity within the ion energy and lifetime ranges observable in these experiments. Ion (a), generated from aziridine was found to be indistinguishable from its open chain isomer CHZ-NH=CH~+. (d).The results closely parallel those previously found for the isoelectronic C2H40+' ions, but the differences in characteristic kinetic energy release are smaller. A simple deuterium exchange labelling experiment may be necessary for the unequivocal identification of C2H5N+' ion structures. JOHN L. HOLMES et JOHAN K. TERLOUW. Can. J. Chem. 54, 1007Chem. 54, (1976.On a CtudiC les pics metastables dus B la fragmentation C2H5N+' + C2H4N+ f H ' dans la premikre rigion libre de champ d'un spectromktre B double focal~sation. On a caractCrisC les structures isomkres des ions C2H5N+' dCriv6s d'une grande variCte de molkules prCcurseurs par la forme de leurs pics metastables et par la libiration d'inergie cinitique. Les identifications furent facilities par des expCriences impliquant des molkules marquees au deutirium dans des positions appropriks. On a montrC que les quatres ions isomkres

“…There has been considerable experimental (1)(2)(3)(4) and theoretical (5, 6) work on the structures, stabilities, and relative energies of various isomers on the C2H40+' energy hypersurface. The isoelectronic C2NHs+' species is one of the principal ions in the mass spectra of nitrogen-containing compounds and five different isomers (1 -5) have been identified (7,8).…”

mentioning

confidence: 99%

An abinitio molecular orbital study of isomers on the C₂NH₅^+• and C₂NH₅ surfaces

Lien¹,

Hopkinson²

1984

. Can. J. Chem. 62, 922 (1984).The structures and relative energies of seven possible CINHs" isomers have been calculated using nb initio molecular orbital theory. Structure optimisations havc been performed with a 4-31G basis set, using both thc restricted (RHF) and unrestricted (UHF) Hartree-Fock methods. The optimum geometries wcre then used for single point calculations using the 6-31G" basis set. The relative energies are 1 < 7 < 5 < 3 = 2 = 6 < 4 . This order is the same, with the exception of 6 , as for isomers on the C2H40+' surface and the relative energies are very similar to those on the C,H,O" surface. The structures of the radical cations C2NHs+' are compared with those of the neutral molecules C2NHs. Faisant appel 5 la thCorie nb irlitio des orbitales molCculaires, on a calculC les structures et les knergies relatives des sept isomkres possibles pour le CINHs+'. On a optimisC les structures ii I'aide d'une base 4-31G et en utilisant les mCthodes restraintes (RHF) et non-restraintes (UHF) de Hartree-Fock. On a ensuite utilisC les geomktries optimales pour faire des calculs en un point unique a I'aide d'une base 6-31G*. Les Cnergies relatives sont dans I'ordre 1 < 7 < 5 < 3 = 2 = 6 < 4 .A I'exception de 6 , I'ordre est le mCme que pour les isomkres sur la surface de CzH40+' et les Cnergies relatives sont trks semblables a celles sur la surface de C2H40". On compare les structures des radicaux cations CINHS+' avec celles des molCcules neutres C2NHS.[Traduit par le journal]There has been considerable experimental (1-4) and theoretical (5, 6) work on the structures, stabilities, and relative energies of various isomers on the C2H40+' energy hypersurface. The isoelectronic C2NHs+' species is one of the principal ions in the mass spectra of nitrogen-containing compounds and five different isomers (1 -5) have been identified (7,8). Deuterium labelling studies have established 5 to be the base peak for pyrrolidine and both 3 and 5 are produced from piperidine (9). From metastable ion studies different ions, given structures 1, 2, 3, and 4 and/or 5, were shown to retain their structural identities prior to fragmentation by loss of hydrogen atom (7), and subsequent studies (8) using collisioninduced dissociation have established that 5 is the dominant ion, with 4 being produced only from aziridine. Ion 2 (or its cis-isomer 6) has also been reported as a minor product in the laser photolysis of methylamine (lo), but no structural information was provided.The transient nature of these ions precludes a detailed experimental study of their structures and even the relative energies of these ions are not known. We now report an ab initio molecular orbital study of the C,NHst' energy hypersurface in which we determine the relative energies of isomers 1 4 6 and we also report details of their structures. All structures were found to be at minima on the surface and an additional structure, 7, not previously mentioned in the literature was found to be at the second lowest minimum. Initally all structures were subjected...