bluuebunny/crossref_metadata_2025_split huggingface dataset:
The mass spectrum of 2‐cyclohexenol: Loss of CH3⋅ and H⋅ from the molecular ion
Authors: Adley Thomas J. , Matteo Guiseppe , Rye Robin T. B. 
Published: May 2005

AbstractMethyl radical and hydrogen atom losses from the molecular ion of 2‐cyclohexenol and deuterium labelled analogues have been studied. For fragmentations occurring in the first field free region, H⋅ loss is a random process, whereas CH3⋅ loss is highly specific involving the C‐1 hydrogen atom and the C‐5 methylene group. A mechanism consistent with these results is proposed.
The loss of a methyl radical and the retro diels—Alder reaction in the electron impact mass spectrometry of 2‐cyclohexen‐1‐ol and related compounds
Authors: Braem Deniel , Gülaçar Fazil O. , Burger Ulrich , Buchs Armand 
Published: May 2005

AbstractThe electron impact mass spectra of 2‐cyclohexen‐1‐ol and of several of its 2H and 13C labelled analogues show that the molecular ions lose a methyl radical by a completely different means from the mechanism described previously. Moreover, the retro Diels–Alder reaction also proceeds in a non‐classical way; in addition to the elimination of an olefinic molecule from unrearranged molecular ions, a second more important route implies a formal 1,3 allylic rearrangement prior to the retro Diels–Alder reaction. The mass spectra of a series of alkyl substituted homologues show that the competition between the two processes is closely related to the size of the olefinic moiety that is expelled.
Structural and stereochemical factors in the mass spectrometry of mono‐ and dimethylbicyclo[3.3.1]nonanes
Authors: Golovkina L. S. , Rusinova G. V. , Sokolova I. M. , Matveeva I. A. , Gervitz G. E. , Petrov A. A. 
Published: May 2005

AbstractThe mass spectra of mono‐ and dimethylbicyclo[3,3,1]nonanes have been studied. In addition to the fragmentation of the bicyclic form of the molecular ion, the latter appears to dissociate from its monocyclic form. Structural isomers and stereoisomers with essential differences in thermodynamic stability may be identified by the quantitative differences in their mass spectra. Stereoisomers with a ‘boat’ conformation of one of the cyclohexane rings have been shown to differ from the stereoisomers with a ‘chair’ conformation of both rings by virtue of higher intensity of odd‐electron ions for the former.
Rearrangement of molecular ions following electron impact: IV—Origin of the [M—28]+˙ ions in the mass spectra of α‐methyl‐2‐decalone
Authors: Jaudon Pascale , Tabet Jean‐Claude 
Published: May 2005

AbstractThe transposition of the molecular ions (ring contraction) of 2‐decalones is demonstrated by a study of the [M–28]+˙ peak and its homologue in labelled products using ionization and appearance energy measurements, and mass analysed ion kinetic energy and collision induced dissociation spectra.
Kinetic energy release and position of transition state during the intramolecular substitution of ionized 2‐benzoyl pyridines
Authors: Schubert Ralf , Grützmacher Hans‐Friedrich 
Published: May 2005

AbstractThe loss of substituents X from molecular ions of ortho substituted 2‐benzoyl pyridines has been investigated as a function of the dissociation energy of the CX bond. Comparison of unimolecular and collisional induced decompositions of the resulting [M  X]+ ions and reference ions arising from 3‐hydroxypyrido[1,2‐α]indole shows that cyclic fragment ions are formed in every case by an intramolecular substitution reaction with the exception of the parent compound (X = H), which gives rise to a mixture of [M  H]+ ions with different structures. The heat of formation of the cyclic ion has been estimated experimentally and by calculation using thermochemical data, and from this value and the appearance energies, the activation energies of the reverse reactions have been evaluated for the different reaction systems. Measurement of the kinetic energy release during the substitution reactions shows that only part of the reverse activation energy is released as kinetic energy. The energy partitioning quotient varies from 0.37 to 0.08 depending on the dissociation energy of the CX bond or the reaction enthalpy. A sudden change in the energy partitioning quotient is observed with increasing exothermicity of the reaction, paralleling the behaviour of similar reaction systems. These results are interpreted as a demonstration of the influence of the variation of transition state position on the energy partitioning quotient.
Gaseous [C2H3O]+ions
Authors: Weber R. , Levsen K. 
Published: May 2005

Abstract[C2H3O]+ions with the initial structures [CH3CO]+,and [CH2CHO]+cannot be distinguished on the basis of their collisional activation spectra, demonstrating that these isomers interconvert at energies below their threshold for decomposition. Self‐protonation of ketene leads to the [CH3CO]+ion, while the [C2H3O]+ion generated from glycerol most probably has the structure of an oxygen protonated ketene [CH2COH]+.
The gas phase structure of some protonated and ethylated aromatic amines
Authors: Maquestiau A. , Van Haverbeke Y. , Mispreuve H. , Flammang R. , Harris J. A. , Howe I. , Beynon J. H. 
Published: May 2005

AbstractThe fundamental processes of protonation and ethylation, occurring in a methane chemical ionization source, have been investigated for a variety of aromatic amines. The positions of protonation and ethylation on the substrate amines were determined by generating isomeric ions either by protonation of neutral ethyl substituted amines or by ethylation of the amines themselves. The product ions were investigated for structural differences via collision induced dissociation and subsequent analysis via mass analysed ion kinetic energy spectrometry. Similarities and differences between mass analysed ion kinetic energy/collision induced dissociation spectra of these isomeric ions were used to determine protonation and ethylation sites for imidazole, benzimidazole, indazole, pyrrole, pyridine and aniline.
Rearrangements of the TMS derivatives of acylglycines
Authors: Fennessey Paul V. , Tjoa Susan S. 
Published: May 2005

AbstractThe investigation of a series of 18 acylglycines as their mono‐ and diTMS derivatives has revealed a set of common ions at [M–28]+˙, [M–43]+, [M–44]+˙ and [M–59]+. These ions are difficult to explain on the basis of simple cleavage of the molecular ion and were shown to be the result of rearrangement processes. The evidence for the rearrangements was derived from studies using deuterium and carbon‐13 labeling as well as high resolution mass spectrometry. The losses from the molecular ion were shown to be a combination of CH3 from the TMS moiety and CO or CO2 from the carbonyl of the glycine portion of the molecules. An understanding of these rearrangements should aid others in the interpretation of acylglycines of unknown structure.
Mass spectra of sterically crowded trialkylsilyl derivatives of nucleosides
Authors: Quilliam Michael A. , Ogilvie Kelvin K. , Sadana Krishan L. , Westmore John B. 
Published: May 2005

AbstractThe electron impact mass spectra of tert‐butyldimethylsilyl‐, cyclo‐tetramethylene‐tert‐butylsilyl and cyclo‐tetramethylene‐isopropylsilyl‐ ether derivatives of ribo‐ and 2′‐deoxyribonucleosides are described in detail. The interpretation of fragmentation pathways of full and mixed derivatives was aided by metastable ion decomposition studies, precise mass and deuterium labelling measurements, and spectra of mixed derivatives containing the ‘passive’ (in these spectra) trimethylsilyl group. The sterically crowded silyl groups have a powerful fragmentation directing effect. Elimination of a bulky radical, R˙ (tert‐butyl or isopropyl), from the molecular ion produces the siliconium ion [MR]+, which is the precursor for most of the other prominent ions in the spectra. These arise from ‘siliconium ion rearrangements’ resulting from the interaction of the positively charged siliconium ion center with electron dense regions (i.e. oxygens) in the molecule, to form cyclic silyloxonium ions which subsequently decompose. Since the interacting oxygen and silicon must be sterically accessible, the fragment ion types and their abundances are very dependent upon structure. Consequently, [MR]+ ions formed from 2′, 3′ or 5′‐O‐silyl groups give rise to different sets of daughter ions which, for the most part, are not found, or have very low abundances, in the mass spectra of underivatized or trimethylsilylated nucleosides. Detailed information on sugar and base moieties and isomeric substitution is readily obtained.
Isomers of the molecular ion of 2,3‐diphenyl‐1,4‐benzodioxin. A comparative study with the different isomeric molecular ions of benzocyclobutenyl derivatives of 1,4‐benzodioxin
Authors: Dagaut Jacques , Fillaux Joëlle , Leblanc Danielle , Dizabo Pierre 
Published: May 2005

AbstractFrom a study of the elimination of carbonylated radicals from 2,3‐diphenyl‐1,4‐benzodioxin and certain specifically deuterated derivatives, it has been possible to calculate the relative abundances of the different isomeric molecular ions formed. A comparison with phenylbenzocyclobutenyl derivatives of 1,4‐benzodioxin indicates that the isomerization schemes are similar.
Secondary ion mass spectrometry of nucleic acid components: Pyrimidines, purines, nucleosides and nucleotides
Authors: Eicke A. , Sichtermann W. , Benninghoven A. 
Published: May 2005

AbstractBiologically important involatile organic compounds including nucleotides, nucleosides, purines and pyrimidines have been analysed by secondary ion mass spectrometry. For the emission of molecule‐like secondary ions small amounts of the substances were deposited as thin layers on silver foils and bombarded with 3 keV [AR]+ ions. All the compounds investigated yielded intense molecular ions of the general composition [M±H]± and [M + Ag]+, but only a few characteristic fragment ions due to simple bond cleavages. Similarities and differences as compared with spectra obtained by other mass spectrometric ionization techniques are illustrated and discussed.
Doubly charged ion mass spectra: 1‐Aliphatic nitriles
Authors: Mathur B. P. , Abbey L. E. , Burgess E. M. , Moran T. F. 
Published: May 2005

AbstractThe doubly charged ion mass spectra for 12 aliphatic nitriles (1–9 carbon atoms) have been obtained using an Hitachi RMU‐7L double focusing mass spectrometer. These spectra show some characteristic features such as extensive loss of hydrogen and the grouping of ions in the spectra into n‐1 groups where n is the number of carbon atoms in the molecule (n<6). There are no indications of HCN or CN loss in the doubly charged ion spectra of the monosubstituted nitriles. SCF calculations of the energy and structure of doubly charged ions in the propionitrile spectra have been carried out.
Electrophilic aromatic substitution under chemical ionization conditions. Methylamine and ammonia as reagent gases
Authors: Luijten W. C. M. M. , Onkenhout W. , van Thuijl J. 
Published: May 2005

AbstractFor compounds C6H5X (XCl, Br, I) under chemical ionization conditions, methylamine causes ipso substitution of X by [NH2CH3]+ and by [NH2]+˙. C6H5F is less reactive; it gives some [C6H5NH2]+˙. Nitrobenzene gives an adduct ion [M+CH3NH3]+, a reduction product ion [C6H5NO2]+˙, and an ion at m/z93, probably a substitution product [C6H5NH2]+˙, but no [C6H5NH2CH3]+. It is also shown that the ion m/z94, formed from nitrobenzene with ammonia as reagent gas, is a substitution product rather than a reduction product ion. Carbonyl compounds C6H5. CO. X give adduct ions and some substitution, mainly [C6H5NH2]+˙.
Application of linked scans in pyrolysis mass spectrometry of polymers
Authors: Holzmann G. , Koßmehl G. 
Published: May 2005

AbstractLinked scans have been used in the pyrolysis mass spectrometry of polymers containing arylene and/or heteroarylene together with vinylene units. This technique based on metastable ions allows the study of characteristic sequences in complex mixtures of degradation ions up to high mass regions. Essential information is obtained concerning the mechanism of polymerization via the Wittig reaction, the pyrolytic and electron impact induced degradation processes and the ion structures which characterize the polymers.
Electron impact induced fragmentation of pyridyl macrocyclic polyethers (crown ethers)
Authors: Whitney Richard R. , Jaeger David A. 
Published: May 2005

AbstractThe mass spectra of pyridyl‐18‐crown‐6 and pyridyl‐15‐crown‐5 were determined. The spectra of five deuterium labeled analogues of pyridyl‐18‐crown‐6 coupled with high resolution data, allowed formulation of fragmentation pathways, which are dominated by several series involving the loss of C2H4O units.
Mass spectrometry of hydroxyammoniocarboxylates: Lactonization of thermally rearranged molecules during field desorption
Authors: Keough T. , Destefano A. J. , Sanders R. A. 
Published: May 2005

AbstractThe field desorption mass spectral behavior of several hydroxyammoniocarboxylates was studied at both low and high emitter heating currents. The molecular weights of these thermally unstable compounds can be determined directly from the low emitter current (<10 mA) field desorption mass spectra, which are dominated by [xM+H]+ and [xM+HCO2]+ ions (1⩾x⩾4). At higher emitter currents (∼20 mA), pyrolytic processes become important. These include intermolecular transfer of a single alkyl group yielding [M+alkyl]+ ions, intermolecular isomerization producing a hydroxyaminoester as the rearranged form of the molecule, and elimination of alcohol from the rearranged molecule, producing γ or δ lactones. The distribution of pyrolysis products does not depend significantly on the length of the carboxylate chain, but does appear to depend upon the chain length of the alkyl substituent on nitrogen. The spectra of molecules containing a long alkyl substituent (e.g. C14H29, C22H45) exhibit relatively high levels of [M+alkyl]+ ions, unlike the spectra of compounds which contain only methyl or ethyl substituents on the quaternary nitrogen. These latter compounds exhibit a relatively greater tendency toward lactone formation.
Studies in negative ion mass spectrometry: XIV—Electron attachment reactions of a series of η6‐arenetricarbonylchromium(O) complexes
Authors: Blake M. R. , Garnett J. L. , Gregor I. K. , Wild S. B. 
Published: May 2005

AbstractElectron attachment reactions of a series of (η6‐arene)tricarbonylchromium(O) complexes have been examined in the gas phase. The electron capture process has been shown to be influenced by the structure of the η6‐arene ligand and its substituents. Whereas (η6‐benzene)‐ and (η6‐mesitylene)tricarbonylchromium(O) undergo dissocative electron capture, or reductive decarbonylation, yielding [MCO]−˙ ions of highest abundance in their negative ion mass spectra, [η6‐(2,2‐dimethylindan‐1,3‐dione)]tricarbonylchromium(O) forms a molecular negative ion which undergoes sequential CO eliminations and finally a demetallation to give the arene radical ion. A localization of charge on the coordinated arene ligand is proposed for the formation of [M]−˙ in this case. (η6‐Methylbenzoate)tricarbonylchromium(O) also forms a molecular negative ion by secondary electron attachment which decomposes by simultaneous and consecutive eliminations of up to four CO molecules. The elucidation of a mechanism and sequence for these CO eliminations has been achieved by synthesizing and examining the negative ion mass spectrum of [η6‐(C6H5·13CO2Me)]Cr(CO)3. The first CO loss in the principal fragmentation pathway occurs solely from the –Cr(CO)3 group of [M]−˙. The effect of para substituent groups on the stabilities of molecular negative ions and their fragmentations has been ascertained using a series of para‐substituted (η6‐methylbenzoate)tricarbonylchromium(O) compounds containing the groups NH2, OH, OCH3, CL and COOMe. The stabilities of the [M]−˙ ions have been rationalized in terms of the Hammett and Taft parameters σP, σI, σRP, σPO and σRO. The overall electronic substituent effect transmitted to the carbonyl groups of the –Cr(CO)3 unit involves both resonance and inductive components. In this series of compounds the stability of [M]−˙ decreases as the electron withdrawing capacities of the para substituents increase.
Temperature dependence of field desorption mass spectra. Investigation of peptide synthesis intermediates
Authors: Sadovskaya V. L. , Andronova T. M. , Merimson V. G. , Rosynov B. V. 
Published: May 2005

AbstractA pulse mode programmer has been developed for field desorption mass spectrometry that provides setting of the emitter heating current during the scans, switching off the emitter heating current during the intervals between consecutive scans and increasing it by 0.5 mA at the start of each scan. Using this heating device, the temperature dependence of field desorption mass spectra of some peptide synthesis products has been studied.
Mass spectra of 2,2′‐bridged biphenyls with 12‐membered heterocyclic bridging rings: 1—Some tetrahydrotetrabenzo[b,d,h,j] [1,6]diazacyclododecines and their precursors, 2,2′‐diaminobiphenyls
Authors: Behnam Basil A. , Hall D. Muriel 
Published: May 2005

AbstractMass spectra of four tetrahydrotetrabenzo[b,d,h,j] [1,6]diazacyclododecines are reported. Loss of phenan‐threne gives 2,2′‐diaminobiphenyl or the appropriate substituted diamine as the base peak in three cases. Substituents ortho to the biphenyl link substantially modify the fragmentation pattern. Mass spectra of the four 2,2′‐diaminobiphenyls have been determined for comparison.
Proximity effects in the electron impact mass spectra of aurones and related compounds
Authors: Goldsack R. J. , Shannon J. S. 
Published: May 2005

AbstractThe principal ions in the electron impact mass spectra of a series of 6‐methoxyaurones have been shown to be due to four separate reactions associated with proximity effects involving the phenyl group and the coumaran‐one residue. A detailed study with labelled derivatives has been supplemented by a study of the vinylogue 2‐cinnamylidene‐6‐methoxycoumaran‐3‐one and compounds in which the aurone phenyl group has been replaced by α‐naphthyl, β‐naphthyl and 9‐anthryl.
Direct exposure chemical ionization mass spectra of explosives
Authors: Yinon Jehuda 
Published: May 2005

AbstractMass spectra of explosives, including TNT, tetryl, nitroglycerin, PETN and RDX have been recorded by direct exposure chemical ionization with isobutane as reagent at source temperatures of 50–100°C. The mass spectra contain major [MH]+ ions, adduct ions and some fragment ions. The configuration of the relative abundances of these ions has been found to be a function of temperature and source pressure. Maximum [MH]+ ion abundance has been obtained at source pressures much lower than normal chemical ionization pressures.
Thienoquinolines: X—The fragmentation of thieno(2,3‐b)quinoline and its derivatives under electron impact
Authors: Soundararajan N. , Palaniappan R. , Ramakrishnan V. T. , Thiruvengadam T. K. , Kanakarajan K. , Natarajan K. , Shanmugam P. 
Published: May 2005

AbstractA study has been made of the fragmentation upon electron impact of thieno(2,3‐b)quinoline and sixteen of its derivatives containing methoxy, methylenedioxy, chloro, bromo, iodo, nitro and methyl substituents. Besides these, the fragmentation patterns of some S‐oxides, and S,S‐dioxides were also investigated. The majority of the spectra contain molecular ions and the principal fragmentation routes involve loss of carbon monosulphide and hydrogen cyanide from the molecular ion. Rearrangement of the molecular ion appears to precede the fragmentation process in the case of S,S‐dioxides. The fragmentation of 4‐methylthieno(2,3‐b)quinoline is closely analogous to that of alkylquinolines. The main features of these spectra can be predicted from the fragmentation pathways proposed for the parent thieno(2,3‐b)quinoline.
The computer processing and interpretation of mass spectral information. VI—computing the isotopic spectrum of assumed composition
Authors: Sukharev Yu. N. , Sizoi V. F. , Nekrasov Yu. S. 
Published: May 2005

AbstractAn interactive program for the computation of an isotopic spectrum of assumed composition whose empirical formula can be represented either as a set of chemical elements or in terms of structural fragments (super‐elements) is described. The core of the program is a table of all isotopes of 82 elements of the periodic table and super‐elements whose list is decided on by the user. The exact mass of isotopic peaks is determined by the program either from the position of the maximum value of the peak abundance or from the position of its centroid. The spectrum printout may be in one of several formats. The interaction with the program is very useful for operators of mass spectrometers in enabling them to estimate and verify assumptions about the elemental composition of spectrum peak groups.
Electron impact induced cyclization ofortho‐substituted diphenylmethanes
Authors: Liehr Joachim G. , Brenton A. Gareth , Beynon John H. , Richter Wilhelm J. 
Published: May 2005

AbstractMass spectra of 2‐hydroxydiphenylmethane and its derivatives are characterized in the upper mass region by an abundant ionm/z165. Metastable ion measurements reveal that this ion is formed from the molecular ion of the parent compound by elimination of H2O and hydrogen. A fluorenyl cation structure is proposed for this ion on the basis of identity of collision induced mass analyzed ion kinetic energy spectra of ionm/z165 generated from 2‐hydroxydiphenylmethane and from fluorene. Four different pathways of formation of a fluorenyl cation are discussed. The contribution of each of these to the genesis of fragmentm/z165 was monitored in a reversed geometry instrument by measuring the first fragmentation in the first field free region and the second fragmentation in the second field free region.
Heat of formation for sec‐butyl cation in the gas phase
Authors: Traeger John C. 
Published: May 2005

AbstractThe ionization energies and [C4H9]+ appearance energies for several 2‐substituted butanes have been measured by photoionization mass spectrometry. Using the stationary electron convention, a 298 K heat of formation of 771±3 kJ mol−1 is derived for the sec‐butyl cation in the gas phase. A value of 747±3 kJ mol−1 is calculated for the proton affinity of trans‐2‐butene.
Mass spectrometry of nitroazoles: 2—the mass spectra of methyl substituted nitroimidazoles
Authors: Luijten W. C. M. M. , van Thuijl J. 
Published: May 2005

AbstractThe mass spectra of six isomers of methylnitroimidazoles are reported and discussed. All compounds exhibit strong molecular ions, along with the characteristic fragmentations of aromatic nitro compounds. In some cases ortho effects—losses of OH., H2O, CHO., CH2O—are observed, due to interactions of adjacent substituents.
The mass spectra of some para substituted triarylphosphines and triarylphosphine oxides
Authors: Marshall Greg , Franks Stephen , Hartley Frank R. 
Published: May 2005

AbstractThe mass spectra are reported for a series of tris(p‐alkylaryl)phosphines and the corresponding phosphine oxides. The phosphines all give [M]+˙ as the base peak except when the phenyl groups are not para substituted. For the oxides [M–H]+ gives the base peak with one exception for which [M]+˙ is the most abundant ion.
Mass spectrometry of metal compounds. Evidence of CO cleavage in and effect of temperature on the mass spectra of chloropentacarbonylmanganese
Authors: Chaudhuri M. K. , Dasgupta H. S. , Roy N. , Khathing D. T. 
Published: May 2005

AbstractThe mass spectrum of Mn(CO)5Cl has been studied at 70 eV and at varying inlet temperatures of 20–250°C. Like the heavier metal carbonyl derivatives, Mn(CO)5Cl exhibits peaks due to carbido fragments. The spectrum run at 100°C shows the characteristic pattern of Mn2(CO)10 which originates from the formation and recombination of the Mn(CO)5 radical. The spectral pattern changes further at an elevated temperature (250°C) showing the formation of Mn2(CO)8Cl2. The effect of pyrolysis has been discussed.