bluuebunny/crossref_metadata_2025 huggingface dataset:
Chemical ionization induced fragmentations of 2‐phenyl‐1,3,2‐dioxaborolanes and 2‐phenyl‐1,3,2‐dioxaborinanes
Authors: Hancock Richard A. , Weigel Helmut
Published: May 2005

Chemical ionization induced fragmentations (with 2‐methylpropane as reagent gas) of 4‐methyl‐ and 4,5‐dimethyl‐2‐phenyl‐1,3,2‐dioxaborolane and 4‐methyl‐2‐phenyl‐1,3,2‐dioxaborinane gave in each case two fragments, a hydrocarbon ion and metaboric acid. Propeae and thence metaboric acid are eliminated from 4,6‐dimethyl‐2‐phenyl‐1,3,2‐dioxaborinane. The mechanisms of the fragmentations are discussed. Under the conditions used 2‐phenyl‐1,3,2‐dioxaborolane and 2‐phenyl‐1,3,2‐dioxaborinane do not fragment.
Effect of substituents on the kinetic energy release in unimolecular decompositions of substituted anisoles
Authors: Florêncio Helena , Vijfhuizen Peter C. , Heerma Wigger , Dijkstra Geo
Published: May 2005

The kinetic energy relased on the loss of a CH3 ⋅ radical from para substituted anisoles appears to depend on the nature of the substituent. The application of the dual parameter equation of Yukawa and Tsuno yields a linear correlation with the T0.5‐values. The mesomeric effect predominates strongly over the inductive effect.
Hydrogen migration in the electron impact induced retro diels‐alder fragmentation of N‐aryl‐4H‐5,7a‐epoxyisoindolines
Authors: Mintas M. , Klepo Ž. , Jakopčić K. , Klasinc L.
Published: May 2005

The electron impact induced fragmentations of the C‐5 unsubstituted and 5‐methyl N‐aryl‐4H‐5,7a‐epoxyisoindolines (where aryl is pheny, p‐tolyl, p‐methoxyphenyl, o‐methoxyphenyl and p‐chlorophenyl) were investigated. The fragmentation patterns deduced were supported by exact mass measurements of prominent ions and by deuterium labelling. The retro Diels‐Alder fragmentation turned out to be a predominant process in all the compounds investigated. In the mass spectra of the 5‐methyl N‐aryl‐4H‐5,7a‐epoxyisoindolines hydrogen migration preceding fragmentation occurred. From the mass spectrum of the specifically deuterated compound it was concluded that the transferred hydrogen originates exclusively from the 5‐methyl group.
Chemical ionization and electron impact mass spectrometry of some organophosphonate compounds
Authors: Sass Samuel , Fisher Timothy L.
Published: May 2005

The application of gas chromatography chemical ionization mass spectrometry to the determination of a variety of alkyl alkylphosphonates, phosphonofluoridates, phosphonothiolates and an amidophosphorocyanidate is described. Comparison is made between the electron ionization and chemical ionization mass spectrometry of these compounds. Chemical ionization mass spectrometry is shown to enhance the capability for identification, especially when a limited sample is available. Results indicate that methane is highly useful for obtaining protonated molecular ions and association ions (formed by the transfer of a reactant ion to a sample molecule) as well as meaningful fragment ions. Ionizing ethylene and isobutane gives protonated molecular ions as base peaks for all of the compounds studied, including those where a lower abundance of the [MH]+ ion is found via methane chemical ionization mass spectrometry. Ethylene is superior to isobutane on the basis of its effectiveness for serving as both a carrier and a reagent gas and gives better sensitivity. Although not an intrinsic part of this present study, analytical sensitivities in the subnanogram range were found.
Water loss from ester molecular ions upon electron impact
Authors: Folk Theodore L. , Wideman Lawson G. , Cottman Kirkwood S.
Published: May 2005

To date, in mass spectral studies of esters, a single reference to loss of water from the molecular ions has been noted. A series of aromatic esters which exhibit that sparsely observed phenomenon are reported herein. Through a combination of synthetic and deuterium labeling studies, support for a unique fragmentation route for the loss of water from these ester molecular ions has been obtained.
Studies in negative ion mass spectrometry. X—Electron capture by a series of tris(hexafluoroacetylacetonato) metal chelates
Authors: Dakternieks D. R. , Fraser I. W. , Garnett J. L. , Gregor I. K.
Published: May 2005

Results of electron capture and negative ion mass spectrometric studies are reported for a series of tris‐chelates of the type Metal. L3, where L refers to the ligand or enolate ion of the β‐diketone 1,1,1,5,5,5‐hexafluoro‐2,4‐pentanedione (hexafluoracetylacetone), and the metals are: Sc(III), Ti(III), V(III), Cr(III), Mn(III), Fe(III), Co(III), A1(III), Ga(III), In(III). The negative ion mass spectra were all relatively simple; the most abundant ions being the molecular and ligand ions for all the metals studied. Reaction schemes have been established to account for the appearance of all significant fragment ions, many of which have been formed as a result of fluorine atom transfer processes. For the transition metal complexes, evidence for elimination of neutral divalent metal fluorides comes from the ion decomposition reactions [Metal.L.F2]−→[L]−, and for the Group III metal complexes, [Metal.L3]−→[Metal.L2]− as well as [Metal.L2]−→[L]− processes indicate that the metals have been reduced as a consequence of the initial electron capture and subsequent fragmentations of metal‐containing ions. The influence of the metal atom and its 3d‐electron configuration has been shown not to affect significantly the electron capture processes. However, the relative instabilities of molecular anions of the transition metal tris‐complexes show an approximately linear dependence on the increasing 3d‐electron populations of the metal ions from Ti(III) to Co(III).
Structure and formation of gaseous [C4H5O]+ ions. III—Ions derived from unsaturated ethers
Authors: Terlouw Johan K. , Burgers Peter C. , Hommes Henk
Published: May 2005

The abundant [C4H5O]+ (m/z 69) ions found in the 70 eV mass spectra of a series of acetylenic, allenylic and unsaturated cyclic ethers are shown to have the following structures: HCC\documentclass{article}\pagestyle{empty}\begin{document}$ \mathop {\rm C}\limits^{\rm + } $\end{document}HOCH3 (e), H2CC—OCH3 (f), (g) and HCCCH2—O\documentclass{article}\pagestyle{empty}\begin{document}$ \mathop {\rm C}\limits^{\rm + } $\end{document}H2 (h). Of these, the cyclic ion g is the most stable: its ion enthalpy (≥ 165 kcal mol−1) is close to that found for the acyclic C3H5\documentclass{article}\pagestyle{empty}\begin{document}$ \mathop {\rm C}\limits^{\rm + } $\end{document}O isomers identified in a previous study. Evidence that these four isomeric [C4H5O]+ ions are stable species with lifetimes ≥ 10−5 s is obtained from their collisional activation spectra, the shape of the metastable peaks and the associated kinetic energy release values for the common loss of CO, thermochemical information and analysis of deuterium and carbon‐13 labelled precursor molecules. It is further shown that loss of X⋅ from ethers of the type XCCCH2OCH3 involves isomerization into energy rich allenyl type ions [(X)HCCCHOCH3]+˙ . These ions undergo loss of X⋅ by simple bond cleavage, yielding, e type product ions, when the CX bond strength is relatively low (XI, Br). When XCl and especially CH3 or H, X⋅ is only lost after rearrangement yielding the cyclic product ion g. The mechanism for this cyclization reaction is related to that proposed in a previous study for the ester→ acid isomerization in the molecular ions of the esters of α, β‐unsaturated carboxylic acids.
Fragmentation of even electron ions: Protonated amines and esters
Authors: Sigsby M. L. , Day R. J. , Cooks R. G.
Published: May 2005

The fragmentation of protonated amines and esters is examined by collision induced dissociation of mass selected ions generated by chemical ionization. Four fragmentation types are observed: (i) loss of an alkane moiety, explicable in terms of a four‐centered reaction, (ii) loss of alkene, also explicable as a four‐centered process, (iii) loss of an alkyl radical, requiring electron unpairing, (iv) losses of other neutral molecules, viz. acids and alcohols from protonated esters, or amines and ammonia from protonated amines. Proposed mechanisms were checked by characterizing selected product ions through their collision induced dissociation spectra. The usefulness of these generalizations is substantiated by the successful prediction of the fragmentation patterns and the order of relative abundances of daughter ions for eight unknowns including some containing functional groups not studied previously.
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

Methyl 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

The 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

The 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

The 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

The 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

[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

The 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

The 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

The 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

From 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

Biologically 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

The 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

For 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

Linked 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

The 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

The 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

Electron 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

A 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

Mass 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

The 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

Mass 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

A 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

An 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

Mass 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

The 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

The 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

The 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

The 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.
Assigning structures to [C2H3O]+ ions
Authors: Terlouw Johan K. , Heerma Wik , Holmes John L.
Published: May 2005

The problem of assigning structures to [C2H3O]+ ions produced from a wide variety of precursor molecules has been readdressed. The identification of the acetyl cation, \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm{CH}}_{\rm{3}} \mathop {\rm{C}}\limits^{\rm{ + }} = {\rm{O}} $\end{document}, from metastable peak characteristics and collisional activation mass spectra appears to be straightforward. The structure \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm{CH}}_{\rm{2}} = \mathop {\rm{C}}\limits^{\rm{ + }} - {\rm{OH}} $\end{document} is also known to exist as a stable ion. A third ion, whose structure may be represented as \documentclass{article}\pagestyle{empty}\begin{document}$ \mathop {\rm{C}}\limits^{\rm{ + }} {\rm{H}}_{\rm{2}} {\rm{CHO}} $\end{document} or magnified image has also been characterized.
Ion current surface for a double focusing mass spectrometer of reversed geometry
Authors: Lacey Michael J. , Macdonald Colin G. , Donchi Kevin F. , Derrick Peter J.
Published: May 2005

Ion currents obtained for fragmentations in a mass spectrometer of reversed geometry have been represented as three‐dimensional surfaces, which are termed ‘ion current surfaces’. In addition to ion current, useful dimensions of the ion current surfaces are a parameter ln(|ρ|) where ρ = (V0/V)(E/E0) and a parameter ln(|m*|) where m* = (V0/V)mB. Each ion reaction occurring in the source and flight path gives rise to a pattern of peaks and ridges on the surface. If the major features of the surface corresponding to each ion reaction are projected onto the zero ion current plane, they are disposed in a characteristic trapezoidal pattern. All simple and linked modes of scanning correspond to cross‐sections of the surfaces, and representing the scanning modes in this light facilitates the identification of ‘cross‐talk’.
Acid catalyzed aldol condensation in the gas phase
Authors: Wesdemiotis Chrysostomos , McLafferty Fred W.
Published: May 2005

The gas phase reaction of acetaldehyde with a Brønsted acid in a chemical ionization source yields protonated crotonaldehyde, as shown by its collisional activation mass spectrum. This is thus analogous to the well known aldol condensation in solution, in which the initial aldol adduct loses water to yield crotonaldehyde. The possibility of a common mechanism for the gas phase and solution reactions is discussed.
A study of the structures of decomposing and non‐decomposing [C4H5N]+˙ ions formed from different neutral species
Authors: Sakurai H. , Jennings K. R.
Published: May 2005

[C4H5N]+˙ ions have been generated from eleven neutral species. From a study of their metastable transitions and the translational energy released in the fragmentation in which C2H2 is lost, it is concluded that [C4H5N]+˙ ions with sufficient energy to decompose do so from a common structure or mixture of structures when they are generated from crotonitrile, allyl cyanide, cyclopropyl cyanide, methacrylontrile, pyrrole, 2‐, 3‐ and 4‐hydroxypyridines and 2‐aminopyridine. The [C4H5N]+˙ ions formed from allyl isocyanide decompose from a different structure and those given by cyclopropyl isocyanide appear to decompose from a mixture of the two structures. Non‐decomposing [C4H5N]+˙ ions were investigated by means of their collision induced decomposition spectra using a B/E linked scan. Six different structures or mixtures of structures are suggested to explain these observations.
Effect of protonation exothermicity on the chemical ionization mass spectra of some alkylbenzenes
Authors: Herman Jan A. , Harrison Ale X. G.
Published: May 2005

The H2, N2/H2, CO2/H2, N2O/H2, CO/H2 and CH4 chemical ionization mass spectra of thirteen C8 to C11 alkylbenzenes are reported. Characteristic hydride and alkide ion abstraction reactions are observed with all reagent gases. The major fragmentation reactions of [MH]+ are olefin elimination to form a protonated arene and arene elimination to form an alkyl ion. From the effect of structure and protonation exothermicity it is concluded that rearrangement of primary alkyl groups to the more stable secondary or tertiary structure occurs prior to alkyl ion formation. A detailed fragmentation mechanism for protonated arenes is proposed. The ‘effective’ proton affinity of the methane‐derived reagent system is estimated to be ∼556 kJ mol−1.
Thermal surface ionization of some complex salts
Authors: Schade U. , Stoll R. , Röllgen F. W.
Published: May 2005

Thermal ionization on the surface of a heated wire is applied to the volatilization products of alkali salts of carboxylic and sulfonic acids, and to quaternary ammonium salts. The mass spectra of the alkali salts exhibit almost exclusively cationized molecules. They provide evidence for the evaporation of intact clustered molecules even under conditions of a slow rate of evaporation of the salts. The method appears to be of interest for selective detection of alkali salts from complex mixtures. With the ammonium salts [R4N]+ ions are formed by thermal surface ionization of intact salt molecules. The evaporation of these molecules could be detected at rather low temperatures.
Comparison of the fragmentations and reactivities of positive and negative ions. Thiocarboxylate ions
Authors: Trenerry V. C. , Stone D. J. M. , Bowie J. H. , Clausen K. , Scheibye S. , Lawesson S.‐O.
Published: May 2005

(1) Thiocarboxylate anions [RCOS]− formed by dissociative secondary electron capture are either stable or fragment to yield [R]−. (2) Thiocarboxylate cations [RCOS]+ formed by charge stripping from [RCOS]−, fragment to form [R]+, [COS]+. and [RCO]+ (not when R=CF3). (3) Aryl hydrogen scrambling is observed in the case of the thiobenzoate cation. Aliphatic hydrogen scrambling is not detected for the thiopropionate cation.
Charge stripping reactions of ions formed from methane, ammonia, water and hydrogen sulphide by protonation and by electron impact
Authors: Proctor C. J. , Porter C. J. , Ast T. , Bolton P. D. , Beynon J. H.
Published: May 2005

The minimum energy, Qmin, necessary to convert an ion m1+ to a doubly charged ion m12+ is obtained for 19 different ions from methane, ammonia, water and hydrogen sulphide by charge stripping using nitrogen collision gas. The ions studied include the [MH]+ ions formed by chemical ionization in a high pressure source. Stable m12+ ions could not be formed in the case of [NH4]+, [NH]+˙, [H2O]+˙ and [OH]+. Even in these cases the value of Qmin could be estimated by studying the fragments formed from the unstable m2+ ions. In several cases, the energy required to form m12+ ions is less than the literature value for the ionization energy of m1+. This is discussed in terms of the possibility of the presence of excited states of m1+ in the present experiments.
Basic questions in mass spectrometry
Authors: Lorquet J. C.
Published: May 2005

The unimolecular dissociation of ionized molecules seldom consists in a direct bond cleavage where the reaction coordinate can be adequately represented by a simple bond stretch. The coordinate which controls the progress of the reaction is not always the reaction coordinate (defined as the degree of freedom whose extension leads to spatial separation of the molecular fragments). The specificity of a dissociation mechanism in a polyatomic species is due to its inherently multidimensional character, i.e. it requires participation of several degrees of freedom. It often consists of a sequence of elementary steps and is therefore controlled by several bottlenecks. The complicated and multistep nature of the reaction mechanism results in a natural tendency towards energy randomization. Radiationless transition from the initial upper electronic states to the ground state of the ion is not always very fast with respect to dissociation. A unimolecular reaction should be seen as a flux in phase space through a critical surface. A transition state corresponds to a surface of least flux, i.e. to a bottleneck of the reaction. For a given elementary step, several may exist, whose positions may vary with energy. The nature of these transition states is not immediately obvious. For instance, they do not necessarily coincide with saddle points or with rotational barriers.
Elimination of water from the molecular ion of cycloheptanol
Authors: Tureček František , Smutek Miloš , Hanuš Vladimír
Published: May 2005

Under electron impact cycloheptanol decomposes by four fragmentation paths: (1) α‐cleavage with subsequent losses of C1‐C5 fragments, (2) elimination of water, (3) loss of the hydrogen atom from C‐1 and (4) loss of the hydroxyl group. The mechanism of water elimination was investigated by means of deuterium labelling. 1,4‐Elimination of water predominates in cycloheptanol, with the stereospecific cis‐1,3‐elimination also being operative. The loss of water is preceded by extensive exchange of the hydroxyl hydrogen with those of the ring. This is attributed to a very facile transannular interaction of the hydroxyl group with the C‐3 to C‐6 positions that are made accessible due to conformational properties of the 7‐membered ring. A kinetic model is proposed, describing migrations of the ring hydrogen atoms.
Electron impact induced hydrogen migrations in organic molecules: IV—novel hydrogen transfers in alkyl o‐methoxybenzoates
Authors: Ramana D. V. , Sundaram N.
Published: May 2005

Simultaneous hydrogen transfers—one from the methoxy group and the other from the alkyl group—to both the oxygen atoms of the ester function result in the formation of a common ion at m/z 152 in the alkyl o‐methoxybenzoates on electron impact. Expulsion of the formyl radical from this ion leads to a fragment resembling the protonated benzoic acid. Another novel feature in these compounds is the loss of H2O from the [MR]+ ion which arises through an ortho effect during a secondary fragmentation process.
High speed acquisition and data processing of peaks in the B‐E plane of a double focusing mass spectrometer
Authors: Warburton G. A. , Stradling R. S. , Mason R. S. , Farncombe M.
Published: May 2005

A technique is described whereby a double focusing mass spectrometer is scanned under data system control to obtain a map of the intensity of the signal transmitted through the collector slit as a function of the electrostatic analyser and magnetic analyser field strengths. Results of processing programs are given, which allow various types of scans within the map to be extracted and presented.
Mass spectrometry of metal compounds: II—mass spectrometric studies of [CF3EMn(CO)4]2, [CF3EFe(CO)3]2(E = S, Se), CF3SeFe(CO)2C5H5and CF3SCr(NO)2C5H5
Authors: Chaudhuri M. K. , Dasgupta H. S. , Roy N. , Khathing D. T.
Published: May 2005

The electron impact induced mass spectra of [CF3SMn(CO)4]2, [CF3SeMn(CO)4]2, [CF3SFe(CO)3]2, [CF3SeFe(CO)3]2, CF3SeFe(CO)2C5H5and CF3SCr(NO)2C5H5are reported. These compounds exhibit weak molecular ion peaks and undergo preferential loss of CO or NO groups. The CO or NO free fragments suffer typical loss of ECF2(E = S, Se) with the simultaneous shift of F from carbon to metal. The ions [FFeC5H5]+and [FCrC5H5]+in the spectra of the cyclopentadienyl compounds prefer expulsion of π‐cyclopentadienyls. The pyrolysis effects on the spectra of the compounds have been studied. An increase in temperature eases the expulsion of ECF2groups from all the compounds and favors the formation of [Fe(C5H5)2]+and [Cr(C5H5)2]+in the cyclopentadienyl compounds.
Doubly charged ion mass spectra: III—N‐alkanes
Authors: Jones B. E. , Abbey L. E. , Chatham H. L. , Hanner A. W. , Teleshefsky L. A. , Burgess E. M. , Moran T. F.
Published: May 2005

Doubly charged ion mass spectra have been obtained for 15 n‐alkane hydrocarbons. Spectra were measured using a Nier‐Johnson geometry Hitachi RMU‐7L mass spectrometer operated at 1.6kV accelerating voltage. Fragment ions, which resulted from CC bond rupture and extensive H loss, dominated the spectra. Molecular ions have not been observed. The most intense ions in the doubly charged ion mass spectra of n‐alkanes were [C2H4]2+, [C3H2]2+, [C4H3]2+, [C5H2]2+, [C6H6]2+, [C6H8]2+, [C7H6]2+, [C7H8]2+, [C8H6]2+ and [C8H8]2+. Appearance energies for forming the prominent doubly charged fragment ions have been measured and range from 27.5 eV to energies greater than 60eV. A geometry optimized SCF approach has been used to compute the energies and structures of prominent ions in the doubly charged mass spectra.
Doubly charged ion mass spectra: IV—chlorinated and brominated alkanes
Authors: Hanner A. W. , Abbey L. E. , Bostwick D. E. , Burgess E. M. , Moran T. F.
Published: May 2005

Doubly charged ion mass spectra have been obtained for 42 chlorinated and brominated n‐alkane (methyl through octyl) hydrocarbons. A double focusing Hitachi RMU‐7L mass spectrometer, operated at 1.6kV accelerating voltage, has been used to measure the spectra. Molecular doubly charged ions have not been observed. Intense fragment ions have been produced from extensive H and halogen loss as well as CC bond rupture of the parent molecule. The most abundant ions in the doubly charged ion spectra observed in this investigation resulted from reactions of [Cl]2+˙, [Br]2+˙, [CCL2]2+, [C2H2Cl]2+˙, [C3H2]2+, [C3HCl]2+, [C3HBr]2+, [C4H3]2+˙, [C4H4]2+, [C4H6Br]2+˙, [C4H8Br]2+˙, [C5H2]2+, [C6H6]2+, [C6H8]2+ and [C7H8]2+. The prominent doubly charged fragment ions formed by electron impact of the smaller halogenated alkanes generally contained halogen, whereas ions of the type [CnHx]2+ were dominant in the spectra of higher molecular weight mono‐ and dihalogenated alkanes. Appearance energies of several ions have been measured. A geometry optimized quantum mechanical SCF treatment has been used to compute energies, charge densities and structures of doubly charged halogenated alkane ions.
Review paper: Design of a mass and ion kinetic energy spectrometer for organic chemical work
Authors: Beynon J. H. , Harris F. M. , Green B. N. , Bateman R. H.
Published: May 2005

The design of a mass spectrometer for the determination of the structural formulae of organic compounds is discussed. The ion‐optical characteristics of electric and magnetic sectors and also of quadrupole mass analysers are considered and the additional information that can be gleaned when such components are combined in various ways is listed. The advantages of using collision cells for inducing fragmentation of selected ion species are listed including those that result when the collision cell is floated at an electrical potential different from that of the incident ion beam. Important performance characteristics are the resolution with which a particular ion may be selected and the resolution with which daughter ions formed from it can be separated. It is concluded, that for instruments comprising three analysing units together with the appropriate collision cells, the most versatile combinations and those with the highest performance are an arrangement consisting of a magnetic sector followed by an electric sector, this being followed either by a further magnetic sector or a quadrupole. The properties of these two systems are compared in detail.
The elimination of carbon monoxide from molecular ions of phenol and other [C6H6O]+˙ isomers
Authors: Walther H. J. , Eyer H. , Schlunegger U. P. , Porter C. J. , Larka E. A. , Beynon J. H.
Published: May 2005

Phenol and five acyclic isomeric compounds have been investigated using electron impact and field ionization techniques, mass analysed ion kinetic energy spectrometry and collision induced dissociation mass analysed ion kinetic energy spectrometry. The kinetic energy release data corresponding to the elimination of carbon monoxide from the molecular ions show that at least two structures of the reactant ion are involved. The electron impact and field ionization collision induced dissociation mass analysed ion kinetic energy spectra indicate that under electron impact conditions, the phenol ion partially isomerizes to another ion structure. An isomerization of about 40% to the structure of cis‐2‐hexen‐4‐yn‐1‐al is in good accordance with the spectral data.