Electron impact studies. LVI. The fluorenyl and phenalenyl cations. The application of metastable characteristics (original) (raw)
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Organic Mass Spectrometry, 1991
The electron impact-induced fragmentation processes of pyrrole-2- ,-3,-2,3- ,-3,4,-2,s and-2,3,karboxylic acids were investigated with the aid of metastable ion, collisional and deuterium labelling experiments. The general behaviour of these compounds is discussed in detail, together with the reasonable structures of the more relevant fragment ions.
Metastable ion decomposition and collisional activation mass spectra of 1,2,3-triarylpropen-1-ones
Organic Mass Spectrometry, 1991
Substituents have been found to have a marked influence on the metastable ion decompositions and collisionally activated (CA) fragmentations of the M" ion of a number of 1,2,3-triarylpropen-l-ones. An attempt has been made to confirm the structures of the rearrangement ions, IC,,H,,I+*, [C13Hll]+, [CljH9l+ and [C,,HS]+' by comparison of their CA spectra with those of the corresponding ions produced from reference compounds. The results imply that [C,,Hloj +. and the M" ions of phenanthrene and diphenylacetylene have a common structure, ICI3H9]+ and the fluorenyl cation have a common structure and [C,,H,] +' and biphenylene molecular ion have a common structure. The available data indicate that the ion at m/z 167 consists of a mixture of structures, likely possibilities being diphenylmethyl, phenyltropylium and dihydrofluorenyl cations.
Organic Mass Spectrometry, 1982
The electron impact mass spectrometric behaviour of a series of macrocyclic-acyclic polyether-ester compounds containing an isoxazole, benzene or pyridine ring is discussed in detail with the aid of exact mass measurements and metastable ions (l i e d scans BIE and If/Q. The nature of unusual [M+H]' species, present in the crown moieties only, is elucidated by means of low electron energy measurements and labelling experiments. The field desorption spectra show only intense peaks corresponding to [M+H]' species and rule out the presence of dimeric moieties.
Rapid Communications in Mass Spectrometry, 2005
A mass spectrometric study of a set of six novel 2-(arylazo)-4-phenylphenols 1–6 was performed. The electron impact spectra were acquired and analyzed for five of the compounds in order to establish a fragmentation pattern. The suggested pathways were investigated and confirmed by means of tandem mass spectrometry (MS/MS) experiments together with high-resolution accurate mass data. However, the sixth molecule, a sodium sulfonate salt, was studied using fast atom bombardment (FAB) ionization in positive and negative modes. In addition, some electronic substituent effects were investigated by analyzing Hammett-McLafferty linear free energy correlations for some peaks derived from the corresponding molecular ions. Also, the role of the OH · · · N hydrogen bond present in the target compounds was analyzed. The roles of these Hbonds were consistent with the corresponding acidity constant values obtained experimentally as well as by theoretical quantum chemistry calculations using HF/6-31 + G(d,p) and B3LYP/6-31G(d,p). Some spectrometric data were correlated with topological properties derived from the atoms-in-molecules (AIM) theory. Copyright © 2005 John Wiley & Sons, Ltd.
The Journal of Physical Chemistry A, 2008
The multiple CF bond character of PhCFMe + ions has been examined by means of theory, vibrational spectroscopy of the gaseous ions, and unimolecular decomposition chemistry. Atoms in Molecules analysis of DFT wave functions gives a CF bond order of n) 1.25 (as compared with n) 1.38 for Me 2 CF + , relative to n) 1 for fluoromethane and n) 2 for diatomic CF +), which is consistent with calculations of adiabatic CF stretching frequencies (ν CF). Experimental gas phase IR spectra, recorded by means of resonant multiphoton dissociation (IRMPD) using a free-electron laser connected to an FTICR mass spectrometer, show good agreement with predicted band positions for five deuterated isotopomers of PhCFMe +. Metastable ion decompositions of deuterated analogues of PhCFMe + show the same HF/DF loss patterns as those produced by IRMPD. The evidence supports the conclusion that PhCFMe ions retain structural integrity until they become sufficiently excited to dissociate, whereupon they undergo intramolecular hydrogen scrambling that is competitive with HF/DF expulsion. Relative rates of hydrogen transposition and unimolecular dissociation are extracted from relative experimental fragment ion abundances. The predominant decomposition pathway is inferred to operate via a five-center transition state, as opposed to a four-center transition state for HF loss from gaseous Me 2 CF + .
Organic Mass Spectrometry, 1990
Mass spectral fragmentations of four norbornaneleoe di-em-and di-endo-fused 1,3-oxazin-2(lH)-ones and four 1,3-oxazine-2(1H)-thiones were examined by means of metastable ion analysis, the collision-induced dissociation technique and exact mass measurement. Under electron impact (EI) conditions all the saturated compounds gave rise to complicated fragmentations, including several rearrangements. For the unsaturated compounds, a retro-Diels-Alder (RDA) process was the most favoured fragmentation pathway, which took place with hydrogen rearrangement to yield RDA + H fragments. The EI mass spectra did not permit isomeric differentiation. Under chemical ionization conditions, stereochemical effects were more perceptible, but isomeric differentiation was still difficult.