bluuebunny/crossref_metadata_2025_split huggingface dataset:
The chemistry of hexahydro‐1,2,4,5‐tetrazines—II: Mass spectra of 1,4‐dialkylhexahydro‐1,2,4,5‐tetrazines and 1,4‐dialkyl‐2,5‐diacylhexahydro‐1,2,4,5‐tetrazines
Authors: Hammerum Steen , Møller Jørgen 
Published: May 2005

AbstractThe mass spectra of twenty‐eight 1,4‐dialkylhexahydro‐1,2,4,5‐tetrazines and 1,4‐dialkyl‐2,5‐diacylhexahydro‐1,2,4,5‐tetrazines (1) have been recorded and interpreted with the aid of deu‐terium labelling, high resolution measurements, and the metastable defocusing technique. The principal fragmentations involve initial scission of ring bonds, particularly C‐N bonds, leading to characteristic ions of mass M/2 and M/2± 1, and to 2,3‐diaza‐1,3‐butadienyl ions (II). In the spectra of acylated compounds, acyl migration occurs within the molecular ion. The elimination of formaldehyde from the principal fragment ion is discussed.
Electron‐impact induced rearrangements of substituted biphenyls
Authors: Safe S. 
Published: May 2005

AbstractThe electron‐impact induced rearrangements of halobiphenyls show substituent equilibration in the molecular ion for the chloro, bromo and iodo isomers. The above halo compounds as well as the fluoro, methyl and methoxybiphenyls all show considerable H/D randomization in the molecular ion or some subsequent decomposition ion.
Mass spectra of macrolide antibiotics. The utility of the N‐oxide derivatives in enhancing fragmentation of the non‐sugar portion of basic antibiotics
Authors: Mitscher L. A. , Foltz R. L. , Levenberg M. I. 
Published: May 2005

AbstractFragmentation of macrolide antibiotics containing amino sugar moieties in the mass spectrometer provides limited structural information because amino sugar fragmentation dominates the spectrum. Formation of the N‐oxide derivative suppresses these processes and allows the non‐sugar portion to make a more substantial contribution to the spectrum. The N‐oxide may be formed in situ.
Spectrographie de masse en série du bornane—II: Amino‐bornanols et dérivés
Authors: Daniel Alfred , Pavia Andrè Armand 
Published: May 2005

AbstractLes auteurs ont étudié les spectres de masse d'un grand nombre d'amino‐bornanols et dérivés et leurs oxazolidines. Une étude comparative des fragments obtenus selon la position de l'amine montre que la rupture entre les carbones 2 et 3 porteurs des substituants reste primordiale aussi bien pour les amino‐2 que pour les amino ‐3 bornanols.L'étude des spectres des oxazolidines et des amino‐alcools, montre que, si dans les premiers la charge semble être également répartie entre les deux hétéroatomes, N et 0, il n'en est pas ainsi dans les amino‐alcools ou l'azote porte préférentiellement la charge.Enfin, si la spectrographie de masse ne semble pas d'une grande utilité pour l'etude de la stéréoisomérie, elle se révèle un moyen de choix pour préciser l'isomérie deposition dans ce type de composé.
Mass spectrometric investigation of bimolecular compounds
Authors: Heunisch George W. , Keen Gary W. 
Published: May 2005

AbstractTwo points involving molecular structure have been investigated using mass spectrometry. First, mass spectra have been obtained that indicate a rapid means for differentiating bimolecular compounds from other structural isomers. Second, the mass spectrometric method has been used to evaluate bonding within bimolecular compounds. Quinone compounds have been reacted with dhydroxybenzene compounds to produce quinhydrone products, and upon mass spectrometric analysis, the quinhydrones decompose to regenerate derivatives of the starting materials. Evaluation of the decomposition products suggests that the hydroxyl hydrogens are involved in a resonance structure, and while in symmetrical quinhydrones, the hydroxyl hydrogens are probably associated equally with each reactant, unsymmetrical quinhydrones generate an unbalanced electronic distribution that eliminates the complete equivalency of the hydrogens.
Mass spectrometric studies on platinum (II) complexes
Authors: Chan T. H. , Wong E. 
Published: May 2005

AbstractSeveral platinum(I1) complexes were subjected to mass spectrometric investigation. The major fragmentation pathways for dichloro‐bis(phosphine) platinum(II) were elucidated to be: (i) successive loss of hydrogen chloride or chlorine depending on the structure of the phosphine, (ii) cleavage of P–R bond with the loss of R group, (iii) the presence of [R1R2R3P—Cl]+ in the mass spectra and (iv) fragmentation of the free phosphine.
Factors determining relative ionic abundances in competing fragmentation reactions
Authors: Harrison A. G. , Finney C. D. , Sherk J. A. 
Published: May 2005

AbstractFor the competing fragmentation reactions [la] and [Ib], it is shown that the relative abundances of [R1]+
magnified image
and [R1]+ are determined by the relative values of the ionization potentials of the corresponding free radicals R1. and R2. In most cases the appearance potentials of [R]+ from RH follow the trends shown by the radical ionization potentials with the result that the appearance potentials can be used to correlate relative ionic abundances. The potential usefulness of relative abundances to estimate radical ionization potentials is illustrated.
Mass spectra and thermochemistry of methyl phenanthrenes. A contribution to the analogy between mass spectral and thermal fragmentation reactions
Authors: Dougherty Ralph C. , Bertorello Héctor E. , de Bertorello M. Martínez 
Published: May 2005

AbstractThe mass spectra of both nonhindered and sterically hindered methyl phenanthrene derivatives follow the patterns established for other alkyl aromatics. The ‘unimolecular’ thermochemistry of these systems parallels the mass spectral fragmentation in a qualitatively predictable way. Generally the major thermochemical products correspond to one of the five most intense fragment ions, and the importance of products which correspond to ions with high appearance potentials increases with increasing temperature of the thermolysis system. On the basis of this empiricism we have outlined a tentative procedure for anticipating the results of thermolysis experiments based on mass spectral data. The use of appearance potential differences to estimate steric strain energies in the compounds studied did not give satisfactory results.
The mass spectra of isomeric hydrocarbons—I: Norbornene and nortricyclene; The mechanisms and energetics of their fragmentations
Authors: Holmes J. L. , McGillivray D. 
Published: May 2005

AbstractThe mass spectra of norbornene, nortricyclene and deuterium labeled derivatives thereof have been studied. The appearance potentials of the ions [C7H10]+·, [C7H9]+, [C6H7]+ and [C5H6]+· have been determined for both compounds and heats of formation of the hydrocarbons have been estimated. Detailed fragmentation schemes are proposed for the molecular ions and it is concluded that they dissociate by essentially different mechanisms which do not involve common intermediates. The structures and energy contents of the primary fragment ions are discussed in detail by comparing energetics, labeling experiments and metastable ion abundances.
Charge exchange spectra of simple ketones
Authors: Turk Jonathan , Shapiro Robert H. 
Published: May 2005

AbstractCharge exchange spectra of three simple 2‐ketones are reported. Comparison of charge exchange data with low voltage electron‐impact spectra provides information on the nature of the electron‐impact energy distribution. The existence of high energy molecular ions which do not decompose in the mass spectral time scale led us to postulate that isolated states or photon emission reactions are operative in the present system.
Loss of CH2O and H2O by stepwise mechanisms in mass spectrometry
Authors: Lacey M. J. , Macdonald C. G. , Shannon J. S. 
Published: May 2005

AbstractExperimental evidence demonstrating reversible hydrogen transfer between specific positions in the molecular ions of anisole and o‐toluic acid suggests stepwise mechanisms for the loss of CH2O and H2O, respectively. Added support for a stepwise mechanism for the loss of CH2O is found in the mass spectra of pyridine and quinoline analogues.
Carbon skeletal rearrangements in 2‐phenylthiophene and 2,5‐diphenylthiophene under conditions of electron‐impact
Authors: Weringa W. D. , Sinnige H. J. M. , Janssen Matthijs J. 
Published: May 2005

AbstractThe mass spectra of 13C‐labelled 2‐phenylthiophenes and 2,5‐diphenylthiophenes were studied. The label distributions for the [HCS]+, [C2H2S]+·, [C8H6]+·, [C9H7]+ and [C7H5]S+ ions from 2‐phenylthiophene and the [HCS]+, [C9H7]+, [C7H5S]+·, and [C15H11]+ ions from 2,5‐diphenylthiophene were interpreted in terms of both carbon skeletal rearrangements in the thiophene ring and migration of the phenyl substituent. The degree of carbon scrambling in the thiophene ring appeared to be almost independent of the electron beam energy. The formation of some of the fragment ions studied seems to be so fast that no carbon scrambling could be detected at all; in neither case was complete scrambling of the carbon atoms of the thiophene ring observed.
Heterocyclic studies—XXV: Mass spectra of some 4‐trifluoromethylpteridine derivatives
Authors: Clark Jim , Yates F. S. 
Published: May 2005

AbstractMass spectra of 4‐trifluoromethylpteridine and nine of its derivatives are recorded. Electron impact induced fragmentations of 4‐trifluoromethylpteridine and its 2‐chloro‐, 7‐methyl‐ and 6, 7‐dimethyl‐derivatives resemble those of pteridine and simple methylpteridines except that loss of a trifluoromethyl radical usually intervenes at some stage. Fragmentation of 4‐trifluoromethyl‐pteridine derivatives with an amino, substituted‐amino, alkoxy or alkylthio group in the 2‐position fragment by a variety of mechanisms. Accurate mass measurements and deuterium labelling were used to help elucidate some fragmentation pathways.
Mass spectra of staphylomycin S components and of related cyclodepsipeptide antibiotics
Authors: Compernolle F. , Vanderhaeghe H. , Janssen G. 
Published: May 2005

AbstractThe electron‐impact induced fragmentation of staphylomycin S (I) and related cyclodepsipeptides (II to V) is mainly initiated by elimination of an azomethin molecule (RCHNR′), i.e. 1,2‐dehydro‐4‐oxopiperidine for I and II, 1,2‐dehydro‐4‐hydroxy‐piperidine for III and IV, and an unknown hydroxy‐1,2‐dehydro‐4‐oxopiperidine for VI. Cyclic imino acids, e.g. a pipecolic acid derivative for I to IV and 4‐hydroxyproline for etamycin (IX) preferentially trigger this reaction. Clearcut evidence for the amino acid sequence is given by the mass spectra of the linear peptides obtained from I, V and IX by alkaline hydrolysis of the lactone function and esterification of the carboxy group.
A comparative study of the mass spectra of stilbene and fluorene
Authors: Güsten H. , Klasinc L. , Marsel J. , Milivojević D. 
Published: May 2005

AbstractA comparative study of metastable peaks formed in the first field free region during the fragmentation of stilbene and fluorene indicates that [M — 1] ion of fluorene and the [M — 15] ion of stilbene have a common [C13H9]+ (m/e 165) ion to only 75%. Demethylation of the stilbene cation leads to some extent to a more reactive [C13H9]+ species with a different structure.
The electron‐impact‐induced fragmentation of some methylated histamines
Authors: Dawborne J. S. 
Published: May 2005

AbstractThe mass spectra of twelve mono‐, di‐ and tri‐methyl substituted histamines are reported and discussed. It is shown that the position(s) of substitution may be deduced from a study of the fragmentation pattern, relative intensity and metastable ions allowing unambiguous identification of structure.
Massenspektroskopische Fragmentierungsreaktionen—II: Ein den ‘Ortho‐Effekt’ vortäuschender Zerfall von Diphenylmethanderivaten
Authors: Budzikiewicz H. , Rullkötter J. , Schiebel H. M. 
Published: May 2005

AbstractEs ist i.a. nicht möglich, zwischen Diphenylmethan‐Derivaten (und analogen Verbindungen), die in o‐Stellung zur CH2‐Brücke substituiert sind, und inren m‐ und P‐Isomeren nur auf Grund des ‘ortho‐Effektes’ zu unterscheiden. Eine Erklärung für dieses scheinbar anomale Verhalten wird gegeben.
Studies in chemical ionization mass spectrometry: Aryl Ketones
Authors: Michnowicz J. , Munson B. 
Published: May 2005

AbstractThe CI mass spectra of aryl ketones, πCOR, were studied and found to give primarily [M + 29]+, [M + 1]+, [M − 1]+, [πCO]+ and [RCO]+ ions. The major change in the spectra with increasing length of the aliphatic side chain was an increase in the [M − 1]+/[M + 1]+ ratio. Increasing sample size was reflected primarily in the formation of [2M + 1]+ ions and a decrease in [M + 1]+ ions. Small amounts of water in the reactant gas reduced the extent of fragmentation action.
The mass spectra of some naturally‐occurring 3,4‐dialkoxy furocoumarins and their nor‐derivatives
Authors: MacLeod J. K. , Nakayama M. 
Published: May 2005

AbstractThe mass spectral fragmentations of several naturally‐occurring 3,4‐dialkoxy furocoumarins from the Halfordia species and their nor‐derivatives have been studied using deuterium labelling and metastable analysis. Halfordin (I), isohalfordin (VI) and halkendin (X) show a common major breakdown pathway involving initial loss of a methyl radical from the 3‐methoxy group followed by expulsion of CO, then loss of C2H3O, the latter fragment containing the methyl group from the 4‐position.
Electron impact studies—LXVII. The mass spectra of alkyl‐1,3‐dithianes
Authors: Bowie J. H. , White P. Y. 
Published: May 2005

AbstractThe mass spectra of 1,3‐dithiane, 2‐methyl‐ and 2,2‐dimethyl‐1,3‐dithiane have been studied by 2H labelling and metastable defocusing. The various molecular ions eliminate S2H. to produce the ions [C4H7]+, [C5H9]+ and [C6H11]+ respectively, each of which scramble the hydrogens either before or accompanying further decomposition. Other processes are complex, but parallel those already reported for 2‐aryl‐1,3‐dithianes.
Electron‐impact and thermal fragmentation patterns of some cyclic fluoroethers
Authors: Cotter J. L. 
Published: May 2005

AbstractThe mass spectra of cyclic fluoroethers of the general formula magnified image (n = 1 to 4) are reported and discussed. Although these spectra show many similar features, those for which n = 3 and 4 contain intense peaks at m/e 63 which are only of relatively low intensity in the spectra of the other two.A similarity between the electron‐impact and thermal fragmentation patterns of these compounds is noted.
Ionization and dissociation of some perfluoroalkylene‐linked silanes and cyclic siloxanes under electron‐impact
Authors: Cotter J. L. 
Published: May 2005

AbstractThe mass spectra of two silanes and two cyclic siloxanes of the general formulae HSi(CH3)2‐C6H4(CF2)nC6H4(CH3)2SiH and magnified image (n = 2 and 3) are reported and discussed. Although some major differences are apparent between the spectra of the two silanes, the fragmentation patterns of the cyclic siloxanes are largely identical.
Heterocyclic studies—XXVIII Mass spectra of some 5‐trifluoromethylpyrimido‐(5,4‐e)as‐triazines
Authors: Clark Jim 
Published: May 2005

AbstractFragmentation of 7‐substituted 5‐trifluoromethylpyrimido(5,4‐e)as‐triazines is dominated by consecutive losses of N2 and HCN from the triazine ring. Deuterium labelling, accurate mass measurements and spectral changes with substitution patterns confirm the fragmentation pathways.Comparison of the spectra with those of corresponding pteridines indicates that the 1,2,4‐triazine ring fragments much more readily than the pyrazine ring.
Electron‐impact‐induced ion fragmentation of polyfunctional N‐cyclohexylcarbamates
Authors: Schildcrout Steven M. , Gebelein Charles G. 
Published: May 2005

AbstractMass spectra at 70, 15 and 10 eV are reported for methyl N‐cyclohexylcarbamate, methyl N‐trans‐2‐iodocyclohexylcarbamate, allyl N‐cyclohexylcarbamate and allyl N‐trans‐2‐iodocyclo‐hexylcarbamate. Principal modes of ion fragmentation including hydrogen and skeletal rearrangements are discussed in terms of individual functional groups and their interaction, and are consistent in many cases with mechanisms previously proposed for other compounds. The effects of the iodo and the allyl groups, when present, predominate in the spectra. The application of McLafferty's ‘active site’ concept to these polyfunctional compounds is found to be useful.
Thermally and electron‐impact‐induced rearrangements of dimethylthioncarbamates in gaseous phase
Authors: Tou James C. , Rodia R. M. 
Published: May 2005

AbstractThe thermally and electron‐impact‐induced rearrangements of the dimethylthioncarbamates to the dimethylthiolcarbamates are discussed. Owing to the competition with the ion fragmentation reactions in the mass spectrometric time, < 10−6 seconds, the extent of the mass spectrometrically observed ion isomerization cannot be predicted from that of the thermal induced one. In the ion fragmentations of the non‐rearranged molecular ions, it was found that the relative abundance of the ion (CH3)2NCO⊕ to the total ionization is larger than that of the ion (CH3)2NCS⊕. This is believed to be attributable to the differences in the dissociation energies of the CS bond and the CO bond and in the stabilities of the two ions.
Mass spectrometric determination of the configuration of 2‐methyl‐and 1,2‐dimethyl‐4‐vinyl‐ethinyl(n‐butyl)‐4‐hydroxyperhydroquinolines
Authors: Wulfson N. S. , Bakaev A. A. , Zaikin V. G. , Akhrem A. A. , Ukhova L. I. , Marochkin A. P. , Bludova G. V. 
Published: May 2005

AbstractThe configuration at C‐2 and C‐4 in the molecules of 2‐methyl‐ and 1,2‐dimethyl‐4‐vinylethinyl(n‐butyl)‐4‐hydroxyperhydroquinolines was determined by mass spectrometry. The principal conclusions concerning the stereochemistry were made on the basis of differences in the values of the I[M−15]+/I[M]+·, I[M−17]+/I[M]+·, I[M−43]+/I[M]+· and I[M−57]+/I[M]+· ratios in the mass spectra of the epimeric vinylethinylic alcohols, and of the I[M−15]+/I[M]+· and I[M−15]+/I[M]+· ratios in the case of the n‐butylic alcohols.
Mass spectra of some steroidal diols
Authors: Wyllie S. G. 
Published: May 2005

AbstractThe mass spectral fragmentations of a number of steroidal 3,5‐ and 4,5‐diols and some derivatives have been examined using high resolution mass spectrometry and deuterium labelling. Although the 3,5‐ and 4,5‐diols have very similar mass spectra those of the derived ketols are quite characteristic. A pathway for the formation of the important m/e 332 ion in the mass spectrum of cholestan‐4β,5α‐diol has been postulated.
Mass spectrometry of hydroxy dicarboxylic acids as trimethylsilyl derivatives. Rearrangement fragmentations
Authors: Petersson G. 
Published: May 2005

AbstractGas chromatography—mass spectrometry offers a convenient method for the separation and identification of hydroxy dicarboxylic acids as open‐chain trimethylsilyl (TMS) derivatives. Mass spectra were studied of aldaric (tartronic, tartaric, pentaric and hexaric) acids and deoxyaldaric (malic, 2‐deoxypentaric, 2‐deoxyhexaric, 3‐deoxypentaric and 3‐deoxyhexaric) acids. The different structural types can be readily identified from their characteristic spectra.The most prominent fragmentations involving the rupture of one bond are the loss of a siliconlinked methyl group and the formation of α‐cleavage ions by carbon chain cleavage. The further decay is characterized by a number of significant rearrangements specific of TMS derivatives. Several of these can be classified as involving migration of a TMS group to an oxygen atom or migration of an ester OTMS group to a silicon atom. Concomitant loss of a stable molecule often provides a driving force.Prominent odd‐electron ions are formed by a McLafferty‐type rearrangement of a TMS group. The decomposition of several even‐electron ions can be regarded as analogous to that rearrangement.
A McLafferty‐type rearrangement of a trimethylsilyl group in silylated hydroxy carbonyl compounds
Authors: Petersson G. 
Published: May 2005

AbstractA McLafferty‐type rearrangement of a trimethylsilyl group is demonstrated. Abundant rearrangement ions are formed for trimethylsilyl derivatives of α,β‐dihydroxy carbonyl compounds. Data are given for a large number of hydroxy acids and hydroxy ketones including aldonic acids, aldaric acids, acyclic ketoses and hydroxy keto acids. A few branched lactones are also shown to rearrange.The positive charge and the unpaired electron are extensively delocalized in the odd‐electron rearrangement ions. Those substituents at the α‐carbon atom which offer a favourable delocalization promote the rearrangement. Spectra of specifically methylated species reveal that migration over larger than six‐membered rings occurs to some extent. An observed dependence of abundance on configuration is associated with steric strains in the transition state.The rearrangement ions are of great diagnostic value in structural analysis. They are relatively more abundant at low electron energies and give rise to the base peak at 20 eV for many compounds. Ions produced by the competing conventional McLafferty rearrangement are less abundant.
The mass spectra of carbon‐13 labeled 2‐hydroxynaphthoquinones
Authors: Moore R. E. , Brennan M. R. , Todd J. S. 
Published: May 2005

AbstractCarbon monoxide is lost from the molecular ion of 2‐hydroxy‐1,4‐naphthoquinone (I) almost exclusively from C‐2 as shown from carbon‐13 labeling studies. The fragmentation scheme originally proposed by Williams for I is not a major process.
Ion‐Molekül‐Reaktionen und Hammett‐Gleichung
Authors: Klotz H.‐D. , Drost H. 
Published: May 2005

AbstractIm Rahmen der Untersuchungen über die Analogiebeziehungen zwischen elementaren Ion‐Molekül‐Reaktionen (IMR) in der Gasphase bestimmten Schritten chemischer Reationen in der Flüssigkeit wurde versucht, den Reaktionsschritt der σ‐Komplex‐Bildung bei der elektrophilen aromatischen Substitutionsreaktion durch eine Protonenübertragungsreaktion zu modellieren. Als Kriterium für die Modellierbarkeit die Hammett‐Gleichung.Eine Gegenüberstellung von Hammett‐σ‐Kontanten und—Stellvertretend für die entsprechenden Geschwindigkeitskonstanten—dem Verhältnis der Wirkungsquerschnitte von unsubstituierten und substituierten Aromaten führte zu keiner die Gültigkeit der Hammett‐Gleicnung voraussetzenden linearen Beziehung. Charakterisiert man demgegenüber die elementare IMR durch die bei der Bildung des σ‐Komplexes frei werdende Energie, die Protonenaffinität PA, zeigt sich eine lineare bzw. allgemein eine gesetzmäßige Beziehung zwischen σ‐Konstante und PA, was auf eine Gültigkeit der Hammett‐Gleichung auch für den Bereich der IMR hindeutet.
Mass spectra of azetidines
Authors: Kostyanovsky R. G. , Markov V. I. , Gella I. M. , Khafizov Kh. , Plekhanov V. G. 
Published: May 2005

AbstractThe mass spectra of azetidine, 2‐methylazetidine, 2‐phenylazetidine, methylene‐bis‐azetidines, their N‐halo‐ and N‐tosyl derivatives, 2‐phenylazetine as well as N,N‐dimethylmethane sulphonamide, N,N‐dimethyl and N,N‐diethyl‐ p‐toluene sulphonamides have been investigated. The fragmentation of azetidine derivatives via the open form of the molecular ion is discussed.
Mass spectrometry of cycloheptatriene derivatives—II: Ring contraction of the molecular ion of 7‐cyanocycloheptatriene. Participation of ring carbon in the loss of HCN (or HNC)
Authors: Venema A. , Nibbering N. M. M. , De Boer Th. J. 
Published: May 2005

AbstractAt an electron energy of 70 eV (nominal) both the [M]+·‐ion and the [MH]+‐ion of the title compound expel hydrogen cyanide. 13C labelling in the cyano group shows that these ions lose—within experimental error—only H13CN when decomposing in the ion source, i.e. when possessing a relatively high internal energy. In the first and second field free region, however, as well as in the ion source at low ionizing energies (9 eV, nominal), H12CN is also eliminated. This phenomenon may be explained by ring contraction of the molecular ion to a six membered ring, possibly initiated by the formation of a norcaradiene structure, which may then rearrange further to a species of higher symmetry. This ring contraction is supported by the occurrence of peaks of low intensity at m/e 78 and m/e 77, due to fragments which are generated in one step from the molecular ion.