bluuebunny/crossref_metadata_2025_split huggingface dataset:
Mass spectrometry of thio analogues of pyrimidine bases: n‐butylthiouracils and i‐propylthiouracils
Authors: Wyrzykiewicz E. , Stobiecki M. , Golankiewicz K. 
Published: May 2005

AbstractThe mass fragmentation of twelve new 2‐ and 4‐alkylthio substituted derivatives of uracils is discussed and fragmentation pathways, elucidation of which was assisted by accurate mass measurements and metastable transitions, are proposed. It has been found that the position of uracil ring thiation may be deduced on the basis of mass spectral fragmentation patterns.
Mass spectroscopy of natural products. V—Mass spectroscopic studies of ring a substituted allobetulane derivatives
Authors: Schmidt J. , Huneck S. 
Published: May 2005

AbstractThe mass spectrometric behaviour of ring A substituted allobetulane derivatives is discussed. The position and nature of a substituent both influence the mass spectral decomposition remarkably. In the case of the epimeric 1‐hydroxy‐ and acetoxy allobetulanes, the mass spectral differences are great enough to distinguish these from each other. The results should yield a general rationalization for other saturated triterpenes having the same A, B, C ring system.
[C3H3O]+ ions; reacting and non‐reacting configurations
Authors: Holmes John L. , Terlouw Johan K. , Burgers Peter C. 
Published: May 2005

AbstractThree [C3H3O]+ ion structures have been characterized. The most stable of these is \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm CH}_{\rm 2} = {\rm CH} - \mathop {\rm C}\limits^ + = {\rm O} $\end{document} its heat of formation ΔHf was measured as 749±5 kJ mol−1. In the μs time frame this ion fragments exclusively by loss of CO, a process which also dominates its collisional activation mass spectrum. The other stable [C3H3O]+ structures, \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm CH}\equiv \mathop {\rm C}\limits^ + - {\rm CHOH} $\end{document} and \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm CH}_{\rm 2} = {\rm C} = \mathop {\rm C}\limits^{\rm + } - {\rm OH}, $\end{document}, were generated from some acetylenic and allenic precursor ions; their heats of formation were estimated to be 830 and 880 kJ mol−1 respectively. The former ion was also produced by the gas phase protonation of propynal. These ions show loss of C2H2 and CO in both their metastable ion and collisional activation mass spectra. The broad Gaussian‐type metastable peak for the loss of CO was shown to consist of two components corresponding to gragmentations having different activation energies.
Evidence suggesting the occurrence of [2+3] cycloaddition products in the ion/molecule reactions of suitably substituted allyl cations and olefins
Authors: van Tilborg M. W. E. M. , van Doorn R. , Nibbering N. M. M. 
Published: May 2005

AbstractThe ion/molecule reactions of allyl cations and 2‐methoxyallyl cations with vinyl methyl ether, 1‐chloro‐2‐ethoxyethene and 1,2‐dimethoxyethene are discussed in terms of [2+3] cycloaddition reactions. Deuterium labelling of the cations has been used for the study of the reaction mechanisms. The appearance of various product ions in these ion/molecule reactions lead to the suggestion that in reactions of allyl cations with alkenes non‐cyclic [C5H5]+ product ions are formed preferentially, but that in reactions of 2‐methoxyallyl cations with alkenes a significant part of the product ions are methoxycyclopentadienyl cations. These observations are ascribed to the stabilizing effect of the methoxy group with regard to the positive charge in the product ions.
Stereochemical effects in the mass spectra of 2‐hydroxy‐, 5‐hydroxy‐ and 2,5‐dihydroxyprotoadamantanes
Authors: Munson Burnaby , Jelus Barbara L. , Hatch Frank , Morgan Thomas K. , Murray Roger K. 
Published: May 2005

AbstractElectron ionization and methane and isobutane chemical ionization mass spectra have been obtained for the four configurationally isomeric 2,5‐protoadamantanediols and the corresponding model monoalcohols. Although the electron impact (both 70 and 15 eV) and methane chemical ionization mass spectra of the 2,5‐protoadamantanediols are distinct, the variations are not large and in general they are difficult to rationalize in terms of specific structural features. In contrast, the isobutane chemical ionization mass spectra of these diols show significant differences which can easily be correlated with sterochemical orientations of the substituents.
Field desorption mass spectral fragmentation of monosaccharide isomers
Authors: Deutsch Joseph 
Published: May 2005

AbstractField desorption ionization of selected monosaccharide isomers by potassium ion attachment in high fields is described. The ionization is obtained with a tungsten wire activated with carbon needles and covered with KH2PO4 salt. In addition to the potassium cationized molecular ions, reproducible fragmentation was obtained at 10 mA and 20 mA typical of the various monosaccharides. For instance, D‐glucose tends to lose a water molecule, whereas D‐fructose loses primarily methanol under similar conditions. Methanol elimination is suggested to be characteristic of furanoidal ketoses and water elimination for pyranoidal aldoses, whereas glycol elimination occurs for furanoidal aldoses.
Stereochemical applications of mass spectrometry: 1—The utility of electron impact and chemical ionization mass spectrometry in the differentiation of stereoisomeric benzoin oximes and phenylhydrazones
Authors: Harrison Alex. G. , Kallury R. Krishna Mohan Rao 
Published: May 2005

AbstractA study of the electron impact and chemical ionization (H2, CH4, and iso‐C4H10) mass spectra of stereoisomeric benzoin oximes and phenylhydrazones indicates that while the former can be distinguished only by their chemical ionization mass spectra the latter are readily distinguishable by both their electron impact and chemical ionization mass spectra. The electron impact mass spectra of the isomeric oximes are practically identical; however, the chemical ionization spectra show that the E isomer forms more stable [MH]+ and [MHH2O]+ ions than the Z isomer for which both the [MH]+ and [MHH2O]+ ions are relatively unstable. In electron impact the Z‐phenylhydrazone shows a lower [M]+˙ ion abundance and more facile loss of H2O than does the E isomer. This more facile H2O loss also is observed for the [MH]+ ion of the Z isomer under chemical ionization conditions.
Aziridinone intermediates in electron impact induced fragmentation of some new hydantoins
Authors: Moskal Janusz , Nagraba Krzysztof , Moskal Alexandra 
Published: May 2005

AbstractMass spectra of some 5‐substituted 1,3,5‐triarylimidazolidin‐2,4‐diones have been determined and the chief fragmentation pathways considered. The fragmentation sequences and ion structures are discussed with the help of the appropriate metastables, precursor ion measurements and high resolution measurements.
Chemical ionization mass spectra of mononitroarenes
Authors: Harrison Alex. G. , Kallury R. Krishna Mohan Rao 
Published: May 2005

AbstractThe H2 and CH4 chemical ionization mass spectra of a selection of substituted nitrobenzenes have been determined. It is shown that reduction of the nitro group to the amine is favoured by high source temperatures and the presence of water in the ion source. The H2 chemical ionization mass spectra are much more useful for distinguishing between isomeric compounds than the CH4 CI mass spectra because of the more extensive fragmentation. For ortho substituents bearing a labile hydrogen abundant [MH  H2O]+ fragments are observed. When the substituent is electron‐releasing both ortho and para substituted nitrobenzenes show abundant [MHOH]+ fragment ions while meta substituted compounds show abundant loss of NO and NO2 from [MH]+. The latter fragmentation is interpreted in terms of protonation para to the substituent or ortho to the vitro function, while the first two fragmentation routes arise from protonation at the nitro group. When the substituent is electron‐attracting the chemical ionization mass spectra of isomers are very similar except for the H2O loss reaction for ortho compounds.
Negative ion field desorption mass spectra of some inorganic and organic compounds
Authors: Ott K. H. , Röllgen F. W. , Zwinselman J. J. , Fokkens R. H. , Nibbering N. M. M. 
Published: May 2005

AbstractField desorption of negative ions can be achieved below the threshold of field electron emission. To this end a mixture of the sample with polyethylene oxide and water was applied to smooth wire cathodes. The mass spectra of some inorganic and organic compounds are reported. Anionization by [CI]− ion attachment is demonstrated with the examples of 20‐hydroxycholesterol and sucrose.
Mass spectrometry of hydroxystilbazoles
Authors: Wyrzykiewicz E. , Łapucha A. , Golankiewicz K. 
Published: May 2005

AbstractThe mass spectral fragmentation of the six 2′‐, 3′‐ and 4′ ‐hydroxy substituted 4‐ and 2‐azastilbenes is discussed and fragmentation pathways, elucidation of which were assisted by accurate mass measurements and metastable transitions, are proposed. It has been found that the position of the hydroxystyryl group in the pyridine ring may be deduced on the basis of mass spectral fragmentation patterns.
The location of olefinic bonds in mono‐ and di‐unsaturated compounds
Authors: Greathead Roger J. , Jennings Keith R. 
Published: May 2005

AbstractThe use of vinyl methyl ether as a chemical ionization reagent gas for the location of olefinic bonds is limited by reactions of various ion with vinyl methyl ether molecules. A 75: 20: 5 mixture of nitrogen/carbon disulphide/vinyl methyl ether suggested by Harrison and Chai gives much cleaner spectra and has been used to study octenes and octadienes. Evidence is presented to indicate the formation of two reaction complexes with octenes and four reaction complexes with unconjugated octadienes. Elimination of olefins from these complexes allows one to infer the positions of the carbon‐carbon double bonds in each type of molecule.
Mass spectrometric decomposition processes of 2‐methyl‐1‐hexene
Authors: Falick A. M. , Gäumann T. , Heusler A. , Hirota H. , Stahl D. , Tecon P. 
Published: May 2005

AbstractUnimolecular decompositions of 2‐methyl‐1‐hexene and several labelled analogues were studied following 70 eV electron impact (normal and metastable spectra) and field ionization (field ionization kinetic measurements). Molecules labelled with 13C in the 1‐position and the methyl position were found to behave essentially identically. This is attributed to rapid transfer of a hydrogen atom mainly from C‐5 to C‐1 (γ‐hydrogen shift). Loss of ethene, propene or propenyl do not involve loss of the methyl carbon or C‐1. All three reactions are better than 90% specific in this respect under all conditions studied. At shorter times, C3H6 loss is the dominant reaction, while at longer times C2H6 loss accounts for >90% of the ion current. It is proposed that at least two distinct pathways for C2H4 loss operate in linear 1‐alkenes, one of which (loss of carbons 1 and 2) is blocked by a 2‐methyl substituent. The [C6H11]+˙ and [C5H10]+˙ ions formed from 13C labelled 2‐methyl‐1‐hexenes fragment in an essentially statistical fashion.
Field ionization mass spectrometry as a facile method for the study of the thermal formation of radicals
Authors: Møller Jørgen , Pedersen Carl Th. , Egsgaard Helge , Larsen Elfinn 
Published: May 2005

AbstractElectron impact spectra of thermolysis products of organic salts heated in the ion source of a mass spectrometer may give rise to organic ions corresponding to the cation of the salt. Field ionization mass spectrometry has been used as a facile method for detemining whether such an ion is due to ionization of the corresponding radical present in the gas phase, or to an electron impact induced fragmentation of a reaction product of higher mass. By comparison of the electron impact and field ionization spectra of a series of N‐methyl pyridinium, tropylium and 1,2‐dithiolylium salts it has been found possible to identify the radicals formed thermolytically, when present.
Photodissociation of protonated β‐diketones in the gas phase
Authors: Reents W. D. , Murray K. J. , Freiser B. S. 
Published: May 2005

AbstractThe gas phase photodissociation spectra of four protonated β‐diketones were obtained and compared with the absorption spectra of the corresponding ions in solution. Protonated 2,4‐pentanedione was observed to undergo the photodissociation process [C5H9O2]+ +hν → [CH3CO]+ +C3H6O with a λmax at 276±10 nm compared with a solution absorption maximum at 286 nm. Protonated 2,4‐hexanedione was observed to undergo the photodissociation processes [C6H11O2]+ +hν → [CH3CO]+ +C4H8O and [C6H11O2]+ +hν → [C2H5CO]+ +C3H6O with a λmax at 279±10 nm compared with a solution absorption maximum at 288 nm. Protonated 3‐methyl‐2,4‐pentanedione was observed to undergo the photodissociation process [C6H11O2]+ +hν → [CH3CO]+ +C4H8O with a λmax at 295±10 nm compared with a solution absorption maximum at 305 nm. Protonated 1,1,1‐trifluoro‐2,4‐pentanedione was observed to undergo the photodissociation process [C5H6F3O2]+ +hν → CF3H+[C4H5O2]+ with a λmax at 273±10 nm compared with a solution absorption maximum at 288 nm. The [CH3CO]+ and [C2H5CO]+ produced photochemically with the first three ions react to regenerate the protonated β‐diketone leading to a photostationary state. Photodissociation of the protonated alkyl β‐diketones is believed to occur from the protonated keto form, whereas photodissociation of protonated 1,1,1‐trifluoro‐2,4‐pentanedione is believed to occur from the protonated enol form. Mechanisms for the observed photodissociation processes are proposed and comparisons with results from related techniques are presented.
The fragmentation of isotetronic acids under electron impact
Authors: Bonini C. C. , Iavarone C. , Trogolo C. , Poulton Gerald A. 
Published: May 2005

AbstractThe mass spectral fragmentation of eleven α‐hydroxybutenolide compounds (isotetronic acids) are reported. The main features are carboxyl and consecutive carbon monoxide expulsions. Masses were determined using high resolution techniques, metastable transitions were detected by defocusing experiments, and pathways were further documented by isotopic labelling experiments.
Mass spectrometry of natural products: VIII—Mass spectrometric studies of ring a saturated gibberellins
Authors: Voigt D. , Adam G. , Franke P. 
Published: May 2005

AbstractThe fragmentation behaviour of gibberellin A1 methyl ester and gibberellin C methyl ester has been studied by means of positive and negative ion mass spectrometry, high resolution techniques and metastable ion transitions. The results obtained allow a mass spectrometric distinction to be made between both structural types.
A flowing afterglow study of [C3H3]− ions generated from the reactions of [OH]− with allene and propyne
Authors: Mackay Gervase I. , Bohme Diethard K. 
Published: May 2005

AbstractFlowing afterglow studies are reported for the rates and modes of reaction of [C3H3]− ions produced from allene and propyne by reaction with [OH]− or by electron impact. Studies with methyl formate provide further evidence for the formation from propyne of two distinct stable species.
Multimetalated carboxylates in a filament in‐beam electron impact mass spectrometer
Authors: Matsumoto Kozo , Kosugi Yoshio , Yanagisawa Masaaki , Fujishima Iwao 
Published: May 2005

AbstractAn in‐beam electron impact mass spectrometer has been modified using a tungsten or platinum filament as an in‐beam probe. With this simple device, metalated organic molecular ion peaks of strong intensities are observed under electron impact conditions. New cluster ions, [(CH3CO2)mLin]+ are detected, where m=3‐6 and n=3, 4. Sodium and potassium acetates give stable dimetalated carboxylate ions, and less stable carboxylate ions are formed from benzoates.
Fragmentation mechanism for the loss of XCY (X and Y = O, OR, S) from 2‐phenyl‐1,3,4‐oxadiazole‐5‐one and related sulfur‐containing compounds
Authors: Bouchoux G. , Hoppilliard Y. , Golfier M. , Guillerez M. G. 
Published: May 2005

AbstractThe fragmentation mechanism for loss of XCY (X and Y = O or S) from 2‐phenyl‐1‐3‐4‐oxadiazole‐5‐one and related sulfur‐containing compounds begins with the breaking of the CN bond of the heterocyclic ring. Then a XCY molecule is ejected with the initial formation of a non‐rearranged ion. The major part of ΔHR0 is associated with the stabilization of this neutral fragment. The initial fragment ion is further rearranged before it decomposes.
Fragmentation of the protonated stereoisomers of 5,7‐Undecanediol and its bis(trimethylsilyl) ether under conditions of isobutane chemical ionization
Authors: Wolfschütz Roland , Schwarz Helmut , Blum Wolfgang , Richter Wilhelm J. 
Published: May 2005

AbstractThe chemical ionization induced fragmentation behaviour of an open chain model compound, 5,7‐undecanediol (meso and d,l stereoisomers), is studied and compared with that of previously studied alicyclic models, e.g. cyclohexanediols (cis and trans isomers). In close analogy to the latter, the major fragmentation processes are the one‐ and twofold loss of H2O from the protonated molecules [MH]+. As borne out by appropriately deuterium labelled analogues, the first loss of H2O is invariably a ‘clean’ heterolysis. The second loss is considerably more complex in that 1,3‐ and 1,4‐elimination processes occur concurrently. While the 1,4‐mode may be a direct elimination process in both types of compounds, the 1,3‐mode is rearrangement induced in both. Whereas skeletal rearrangement (ring contraction) precedes this 1,3‐elimination in the alicyclic models, hydrogen rearrangement (1,2‐hydride shift) precedes it in the open chain model. No pronounced stereochemical effect is observed on the mechanistic course of the elimination processes, but is observed in their relative ease. The trimethylsilyl ethers of the stereoisomers of 5,7‐undecanediol are also studied for analogous reactions, and are discussed in this context.
Reaction of cyclohexanone with [NH4]+ under chemical ionization conditions. 1—formation of protonated unsubstituted imines
Authors: Tabet J. C. , Fraisse D. 
Published: May 2005

AbstractHigh resolution and metastable decomposition spectra of the ions [M + NH4]+ (and [M + ND4]+) formed by reaction of [NH4]+ (and [ND4]+) with cyclohexanone have been measured. The results provide evidence that the m/z 98 ion, which is abundant in the chemical ionization (NH3) spectrum of cyclohexanone, is in fact composed of two isobaric ions: a protonated imine ion and the molecular ion of cyclohexanone. The former is formed by a mechanism analogous to that occurring in solution.
The modern mass spectrometer—a complete chemical laboratory
Authors: Porter C. J. , Beynon J. H. , Ast T. 
Published: May 2005

AbstractUsing nitrobenzene as an example, various ways in which a contemporary mass spectrometer can be utilized to yield a wealth of information about the compound studied are reviewed. Applying a variety of different techniques and procedures, in addition to the conventional low resolution mass spectrum, the following nitrobenzene spectra have been obtained: collision induced dissociation mass spectrum, mass analysed ion kinetic energy spectra, collision induced dissociation mass analysed ion kinetic energy spectra, spectra obtained at constant B/E, spectra obtained at constant B2/E, high voltage scans of metastable ion fragmentation processes, consecutive fragmentations in different field free regions, charge exchange mass spectra, charge stripping mass spectra, doubly charged ion mass spectra, chemical ionization mass spectra, negative ion mass spectra, negative ion mass analysed ion kinetic energy spectra, negative ion mass analysed ion kinetic energy collision induced dissociation spectra, charge inversion spectra, etc. The complementary types of information available from the above studies are discussed to show the unique versatility of mass spectrometry as a technique for the examination of organic compounds.
The mass spectrum of isopropyl o‐toluate
Authors: Tajima Susumu , Yanagisawa Tamae , Azami Tadashige , Niwa Yoshio , Tsuchiya Toshikazu 
Published: May 2005

AbstractThe formation of an [M + 1]+ ion and the fragmentation of isopropyl o‐toluate have been investigated by the deuterium labelling technique and kinetic energy release measurements. The hydrogen atom involved in the [M + 1]+ ion formation does not originate from a specific part of the molecule, but from all parts. A small amount of hydrogen exchange between the secondary carbon atom in the isopropyl group and the carbon atoms in the tolyl group takes place prior to decomposition of the molecular ion into the m/z 136 ion by a McLafferty rearrangement. Either almost complete scrambling of the hydroxyl hydrogen atom and the methyl hydrogen atoms in tolyl group or an almost equilibrated exchange of the hydroxyl hydrogen atom with one of the remaining hydrogen atoms in tolyl group also takes place prior to the elimination of a water molecule from the intermediate m/z 136 ion.
Mass spectrometry of trialkylsilyl and acyl derivatives of 2′‐deoxynucleosides
Authors: Quilliam Michael A. , Ogilvie Kelvin K. , Westmore John B. 
Published: May 2005

AbstractThe electron impact mass spectra of monosilyl and mixed acyl‐silyl derivatives of 2′‐deoxynucleosides are described in detail. (Silyl = tert‐butyldimethylsilyl, cyclo‐tetramethylene‐isopropylsilyl, or cyclo‐tetramethylene‐tert‐butylsilyl; acyl = acetyl or trifluoroacetyl.) The interpretation of the fragmentation pathways was aided by metastable ion decomposition studies, precise mass and deuterium labelling measurements. Mass spectrally, the acyl substituents are mostly ‘passive’ and have (with possibly one exception) little fragmentation directing capability. In contrast, the silyl groups have powerful fragmentation directing properties. Elimination of the bulky alkyl 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 centre with the 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 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.
Loss of methyl radical from some small immonium ions: Unusual violation of the even‐electron rule
Authors: Bowen Richard D. , Harrison Alex G. 
Published: May 2005

AbstractSeveral small immonium ions of general formula \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm R}^{\rm 1} {\rm R}^{\rm 2} {\rm C = }\mathop {\rm N}\limits^{\rm + } {\rm R}^{\rm 3} {\rm CH}_{\rm 3} $\end{document} (R1, R2, R3 = H or alkyl) eliminate .CH3; this reaction occurs in the mass spectrometer in both fast (source) and slow (metastable) dissociations. Such behaviour violates the even‐electron rule, which states that closed‐shell cations usually decompose to give closed‐shell daughter ions and neutral molecules. The heats of formation of the observed product ions (for example, [(CH3)2CNH]+.) can be bracketed using arguments based on energy data. Deuterium labelling results reveal that the methyl group originally bound to nitrogen is not necessarily lost in the course of dissociation. Thus, for instance, \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm{(CH}}_{\rm{3}})_2 = \mathop {\rm{N}}\limits^{\rm{ + }} {\rm{HCD}}_{\rm{3}} $\end{document} eliminates both CH3. and CD3., via different mechanisms, but very little CH2D. or CHD2. loss occurs.