bluuebunny/crossref_metadata_2025_split huggingface dataset:
Stereoisomeric effects on mass spectra—II: The isomeric methyldecalins
Authors: Meyerson Seymour , Weitkamp A. W. 
Published: May 2005

AbstractMass spectra of the four stereoisomeric 1‐methyldecalins and the four 2‐methyldecalins have been measured. For each set of stereoisomers, the order of relative intensity of the parent‐less‐CH3 ion, but not of the parent ion, parallels the order of relative stability of the molecules. The correlation suggests that loss of the methyl group from the members of each set of stereoisomers leads to a common product, with the differing conformational energies converting into differences in vibrational energy, which in turn lead to differing extents of further decomposition.
Mass spectrometry in structural and stereochemical problems—CLXXII: The electron‐impact promoted fragmentation of 1,2‐cyclohexanediol
Authors: Strong M. Karen , Djerassi Carl 
Published: May 2005

AbstractThe mass spectra of 1,2‐cyclohexanediol and important data from the spectra of four deuterium labeled analogs have been recorded and mechanistic rationalizations are given for the most important degradation processes observed. Multiple mechanisms are required to explain the indicated peak shifts in the labeled analogs. Particularly relevant is the initial loss of water from the molecular ion, which involves at least four distinct processes.
Mass spectrometric studies on gibberellins
Authors: Takahashi Nobutaka , Murofushi Noboru , Tamura Saburo , Wasada Nobuhide , Hoshino Hiroko , Tsuchiya Toshikazu , Sasaki Shin‐Ichi , Aoyama Tetsumi , Watanabe Eiji 
Published: May 2005

AbstractBased on the element maps of twenty‐two gibberellin methyl esters fragmentations are discussed, which are characteristic of the common structural features as well as structural modification in gibberellin homologues.
The steric effect as a mechanistic tool in mass spectral decompositions. Comments on the activated complex for the loss of no from substituted nitrobenzenes
Authors: Bursey Maurice M. 
Published: May 2005

AbstractThe effect of ortho substituents in nitrobenzence radical cation decompositions are discussed for non‐interacting halogen substituents. These effects are distinct from those of the same substituents in the meta and para positions, and support previous indications that ring position identity is retained in nitrobenzene molecular ions. More importantly, the steric effect of the halo substituents may be gauged from these data; it indicates that several previously suggested mechanisms for the loss of NO must be reconsidered. The existence of steric effect in very well defined systems may be used as a structural tool in organic mass spectrometry.
Relative free radical stabilities from α‐cleavage of β‐substituted N‐ethylanilines
Authors: Shapiro Robert H. , Turk Jonathan 
Published: May 2005

AbstractThis paper describes a direct appearance potential difference method, which is employed to determine, qualitatively, relative free radical stabilities. The method appears to be of general value since the starting materials (β‐substituted N‐ethylanilines) are relatively simple to prepare and because the dominant electron‐impact reaction is the one which releases the free radical under investigation.
Skelettumlagerungen Unter Elektronenbeschuss—IV: Zur Struktur der C13H9‐ und C12H9N‐Ionen bei Benzylidenaminobenztriazolen
Authors: Rapp U. , Staab H. A. , Wünsche C. 
Published: May 2005

AbstractDie Hauptfragmentierung des 1‐(Benzylidenamino‐) benztriazols führt über eine Skelettumlagerung zu dem [C13H9]+‐Ion als. 2‐(Benzylidenamino‐) bildet ebenfalls über eine Skelettumlagerung ein [C12H6N]+‐Ion von beträchtlicher Intensität. Durch Appearance potential‐Massungen wird gezeigt, daß für diese ionen eine Fluorenyl‐bzw. Carbazol‐Struktur ausgeschlossen werden kann.
Field ionization mass spectrometry—II: Benzyloxycarbonyl and t‐butyloxycarbonyl derivatives of some simple peptides
Authors: Brown Peter , Pettit George R. 
Published: May 2005

AbstractA brief discussion is given of some factors that merit consideration in the analysis of peptides by mass spectrometry, with emphasis on sequence determination. The first systematic study of simple peptides by field ionization (FI) is described, and comparison made with the corresponding electron‐impact (EI) ionization spectra, both at low resolution (approx. 1500). The substances examined were either benzyloxycarbonyl or t‐butyloxycarbonyl derivatives of di‐through pentapeptide methyl esters, containing the amino acids glycine, alanine, leucine, serine, threonine, proline and tyrosine. The incidences of sequence‐characteristic cleavage peaks and rearrangement ion peaks were both slightly lower in the FI than the EI spectra, although the peak relative intensities generally were higher under FI conditions.
Analysis of organic salts by laser ionization
Authors: Vastola F. J. , Mumma R. O. , Pirone A. J. 
Published: May 2005

AbstractAlkali salts of 1‐hexyl sulfonate were ionized by laser irradiation and the positive ions were analyzed by time‐of‐flight mass spectrometry. The sodium, potassium, rubidium and cesium salts produce relatively simple spectra. The major organic ions observed are due to the salt plus a cation or the dimer plus a cation. No molecular or fragment ions were detected. The instrumentation and the method of interpreting these data are described.
The effect of substituents on the average internal energy of benzoyl ions generated from N‐(substituted‐phenyl)benzamides
Authors: Shapiro Robert H. , Turk Jonathan , Serum James W. 
Published: May 2005

AbstractThe [56.5*]/[105]+ ratios observed in the spectra of N‐(nitrophenyl)benzamides are greater than those observed in the spectra of N‐(methoxyphenyl)benzamides. These results differ from those observed in the spectra of monosubstituted benzophenones. An explanation, based on energy distribution and breakdown curves, is employed to rationalize these results, as well as other phenomena reported in the literature.
Correlation of the mass spectral and photochemical behavior of some 1,3‐dieneiron tricarbonyl complexes
Authors: Dauben William G. , Lorber Milton E. 
Published: May 2005

AbstractThe mass spectra of a number of 1,3‐dieneiron tricarbonyl complexes have been investigated. It has been shown that complexes derived from substituted 1,3‐cyclohexadienes lose hydrogen or methane in the mass spectrometer to lead predominantly to the formation of odd electron ions containing the iron atom bonded to an aromatic system. The fragmentation route followed by these complexes and those from acyclic dienes is compared.
Mass spectrometric analysis of N‐substituted cyclohexene‐1,2‐dicarboximides
Authors: Mitchell Earl D. , Waller George R. 
Published: May 2005

AbstractBoth low and high resolution mass spectra of cis‐4‐cyclohexene‐1,2‐dicarboximide, its N‐methyl, N‐ethyl, N‐n‐propyl and N‐n‐butyl derivatives, and cyclohexane‐1,2‐dicarboximide were obtained at 70 eV. Each of the spectra exhibited characteristic nominal ions at masses 151, 136, 123 and a group of ions at masses 77, 78, 79, 80 and 81 of which m/e 80 was always the base peak except for the unsubstituted cyclohexane compound. The m/e 77 to 81 fragments are composed of carbon and hydrogen and derived from the cyclohexene ring. The ions possessing higher masses are heterocyclic and certain of them show doublets and triplets. Evidence for a 1,3 hydrogen migration was supplied by studies with the N‐(ethyl‐2‐d3) derivative and evidence for a 1,4 migration by the N‐(n‐propyl‐3‐d3) derivative.
Mass spectrometry—II: The unimolecular decomposition of benzaldehyde azine in the gas phase induced by electron‐impact
Authors: Scheppele Stuart E. , Grigsby Ronald D. , Kinneberg Keith F. , Mitchell Earl D. , Mannan Claude A. 
Published: May 2005

AbstractThe mass spectra of benzaldehyde azine‐α, αA‐d2 (III) and benzaldehyde azine‐d10 (IV) reveal that both ring and α hydrogen are lost from the molecular ion of benzaldehyde azine (II) in forming the [M –1] ion. Data from the spectra of III and IV at 70 eV and reduced ionizing voltages are consistent with the existence of two competing pathways producing [M –1] ions. Rearrangement ions are observed in the spectra of II. Randomization is unimportant in the electron‐impact‐induced fragmentation reactions of II. The rearrangement‐fragmentation reactions for II in general parallel those previously observed for acetophenone azine (I).
The mass spectra of diaziridinones
Authors: Lengyel István , Greene Frederick D. , Pazos José F. 
Published: May 2005

AbstractThe electron‐impact induced fragmentation of four N,N′‐di‐t‐alkyl‐substituted diaziridinones (I to IV) has been studied by both conventional and high resolution mass spectrometry. All diaziridinones exhibit weak molecular ions. Ejection of an alkyl isocyanate, corresponding to the N‐alkyl substituent, from the molecular ion, is a dominant and general fragmentation process. Isocyanate‐type odd‐electron fragment ions occur only in III and IV (where at least one R group is phenyl) and are of low abundance. Elimination of a hydrocarbon radical from the tertiary alkyl substituents is observed in all compounds investigated. McLafferty rearrangement with elimination of a neutral alkene occurs in all compounds. Abundant even‐electron hydrocarbon ions corresponding to the mass of the N‐alkyl substituent are prevalent. The complete absence of elimination of carbon monoxide is noted. Loss of oxygen from the [M  RCH2]+ species has been confirmed by accurate mass measurement. Several remarkable rearrangement reactions have been uncovered by high resolution studies and deuteration experiments.
Ortho‐rearrangement in the mass spectra of diphenylmethanes
Authors: Scott Ward M. , Wacks Morton E. , Steelink Cornelius , Fitzpatrick J. D. 
Published: May 2005

AbstractThe mass spectra of all possible methyl substituted derivatives of 3,3′,5,5′‐tetramethyl‐4, 4′‐dihydroxy‐diphenylmethane are recorded. The direct influence of steric hindrance to free rotation about the aryl‐methylene bonds results in the progressive importance of ortho‐rearrangement in the ionization‐dissociation pathways of these compounds.
Mass spectra of nucleoside derivatives
Authors: Dolhun J. J. , Wiebers J. L. 
Published: May 2005

AbstractThe mass spectra of derivatives of uridine, adenosine, cytidine and guanosine are recorded. Derivatization techniques include permethylation, acetylation, trifluoroacetylation, trimethylsilylation and the synthesis of 2′,3′‐O‐isopropylidenes and 2′,3′‐O‐phenylboronic esters. Sequential derivatization by a selective combination of some of these procedures results in nucleosides which are blocked with a characteristic group at the cis 1,2 diol position, and, which contain other substituent groups that enhance the volatility of the compound. The specific substitution at the cis‐glycol region has been shown to be particularly useful in asymmetrically derivatizing dinucleoside phosphates since certain fragment ions from their mass spectra indicate the sequence of the two nucleoside components. Sequence isomers such as adenylyl‐(3′‐5′)‐uridine and uridylyl‐(3′‐5′)‐adenosine can be unambiguously distinguished.
Spectrométrie de Masse—IV: Fragmentation des Dicétones—ϵ
Authors: Kossanyi Jean , Mogto Josué Kom 
Published: May 2005

AbstractLa dégradation induite par bombardement électronique de dix dicétones‐ϵ symétriques a été investiguée; une rationalisation des mécanismes de fragmentation, confirmée par deutération, a pu étre proposée pour expliquer les dégradations observées. La transposition de McLafferty ne représente pas, ici, l'une des principales fragmentations bien qu'une double transposition de ce type soit présente pour les composés à chaíne longue. Une attention particuliére a été prétée aux ions résultant de la perte d'eau et de la perte d'dne molécule d'ethyléne à partir de l'ion moléculaire, pertes qui font intervenir un intermédiaire du type cyclobutanol comme dans le cas des photoisomérisations de ces composés.
Electron‐impact studies of ms‐porphyrins
Authors: Adler A. D. , Green J. H. , Mautner M. 
Published: May 2005

AbstractThe mass spectra of several ms‐porphyrins and their metalloderivatives have been obtained on an AEI MS‐902 mass spectrometer. The main features of these spectra are very stable parent peaks and relatively abundant doubly‐charged and triply‐charged fragments. Metal substitution has a drastic effect on the fragmentation pattern, which discloses formation of fragments with a stable composite π‐electron ring, including Hückel rings. Ion‐molecule reactions giving products up to [M + 124]+ are also reported.
Mass spectra of the substituted quinuclidines
Authors: Kostyanovsky R. G. , Mikhlina E. E. , Levkoeva E. I. , Yakhontov L. N. 
Published: May 2005

AbstractThe mass spectra of the quinuclidine‐2 (and ‐3)‐ones and other functional derivatives of quinuclidine as well as 2‐azaquinuclidine and benzoquinuclidine have been investigated. The fragmentation through the open form of the molecular ion and the applicability of Bredt's rule to amine fragmentation of the bridgehead nitrogen bicyclic systems are discussed.
Thermal and mass spectrometric fragmentation of esters of deuterated long chain carboxylic acids
Authors: Sun Kwok K. , Hayes Herbert W. , Holman Ralph T. 
Published: May 2005

AbstractA method combining thermal fragmentation and mass spectrometry for the determination of the position of double bonds in an unsaturated ester is presented. The thermal fragmentation of methyl esters of deuterated long chain carboxylic acids yields a homologous series of olefins plus a homologous series of unsaturated esters. The positions of the deuterium atoms in the original ester are revealed by the deuterium content of its fragments as determined by mass spectrometry. Therefore, the positions of double bonds of a polyunsaturated acid can be determined by pyrolysis after saturation by deuterium. The structures of the unsaturated fragments are ascertained by mass spectrometric method, and the formation of the ion [M – 32] in the mass spectrometric fragmentation of unsaturated methyl esters is studied by means of deuterium labeling.
Electron‐impact promoted fragmentation of some substituted isoxazolidines
Authors: Duffield A. M. , Buchardt Ole 
Published: May 2005

AbstractA series of substituted isoxazolidinylacetophenones (II to VI) have been shown to fragment subsequent to electron‐impact in a generally predictable fashion. One characteristic fragmentation of all the compounds investigated was the loss of H2O2 from their respective molecular ions.
Mass spectrometry in structural and stereochemical problems–CXCV: The structure of the [C6H6O]+˙ ion in the spectrum of phenyl alkyl ethers
Authors: Woodgate Paul D. , Djerassi Carl 
Published: May 2005

AbstractThe [C6H6O]+˙ ion from C6H5OC4H9 is structurally similar to the molecular ion from phenol as demonstrated by 13C labeling.
Charge localization in the retro‐Diels‐Alder fragmentation of tetralins
Authors: Lightner D. A. , Steinberg Frank S. 
Published: May 2005

AbstractThe electron‐impact induced retro‐Diels‐Alder reaction of 5‐ and 6‐substituted tetralins has been examined. Most electron‐donating groups at C‐5 retard the fragmentation relative to tetralin; whereas, electron‐withdrawing groups slightly increase the fragmentation.
Kinetic studies in mass spectrometry–VII: Competing cleavage and rearrangement processes in molecular ion decomposition reactions
Authors: Brown Peter 
Published: May 2005

AbstractApparently competing cleavage and rearrangement reactions in a series of molecular ions have been studied by ionization and appearance potential methods, and by determination of the electron energy dependence of both normal and metastable daughter ion peak intensities. The processes investigated were (i) [M  CH3] vs. [M  CH2O] in anisole; (ii) [M  OC6H5] vs. [M  CO] in phenyl ether; (iii) [M  NO2] vs. [M  NO] in nitrobenzene; (iv) [M  C3H7] vs. [M  C2H4] in butyrophenone: (v) [M  C3H7] vs. [M  C3H6] in n‐butylbenzene; (vi) [M  CH2OH] vs. [M  CH2O] in 2‐phenylethanol; (vii) [M  CH3CO2] vs. [M  CH2CO] in benzyl acetate; and (viii) [M  C4H9O] vs. [M  C4H7] in n‐butylbenzoate. The results are interpreted in terms of k vs. E curves with very different frequency factors for the two reaction types. Appearance potentials of metastable ions for the rearrangement reactions have also been measured.
Mass spectrometry in structural and stereochemical problems–CXCIV: The mass spectrometric fragmentations of steroidal sapogenins
Authors: Faul William H. , Djerassi Carl 
Published: May 2005

AbstractThe characteristic mass spectral fragmentation patterns of the basic structure of the steroidal sapogenin, (25R)‐5α‐spirostan, have been elucidated through the preparation of analogs with deuterium labels at positions 11, 12, 14, 15, 16, 17, 20, 21, 23, 24, 25, 26 and 27. In addition, the effects of a change of stereochemistry at positions 14 and 20, of the introduction of oxygencontaining functionalities mostly in ring F, and of the incorporation of olefinic unsaturation have been determined through synthesis of many examples.
Mass‐spectrometric studies on alkylated 6‐thiopurines
Authors: Deutsch Joseph , Neiman Zohar , Bergmann Felix 
Published: May 2005

Abstract6‐Thiopurine and its N‐ or C‐alkyl derivatives all form an [M – 1]‐ion upon fragmentation. In the 7‐alkyl derivatives, this ion represents the major component of the spectrum. This is ascribed to formation of a five‐membered thiazoline‐like ring. Similar ring formation stabilises the [M – 1]‐ion in the 7‐methyl derivatives of hypoxanthine, adenine and 6‐selenopurine.
Mass spectral fragmentations of aminoketones in which charge is not localized exclusively on nitrogen
Authors: Wagner Peter J. 
Published: May 2005

AbstractThe low resolution mass spectra of α‐dimethylaminoacetophenone and γ‐dimethylaminobutyrophenone are compared to those of δ‐methylhexanophenone and dimethyl n‐butylamine as well as to those of α‐dimethylaminoacetonitrile and γ‐dimethylaminobutyronitrile. Analysis indicates that significant fractions of the fragmentations of the aminoketones are directed by the carbonyl. In particular, McLafferty rearrangement of the γ‐aminoketone is favored over α‐cleavage from nitrogen at ionizing voltages below 15 eV. Although the overall fragmentation patterns are presumably determined both by the distribution of charge and by the relative rates of the fragmentation processes available to the two ionized groups, the intrinsic rates for α‐cleavage at ionized nitrogen and at ionized carbonyls appear to be very similar. Kinetic analysis suggests that 26% of the charge resides on the carbonyl in the γ‐aminoketone molecular ion. The extent of delocalization of charge in any aminoketone may be partially controlled by the extent of spatial overlap of the two groups. Correlations of mass spectral behavior with photochemical behavior are thus limited because electronic excitation is more localized in the lowest excited states of molecules than charge is in electron‐impact produced molecular ions.
Electron‐impact‐induced ring condensation. The mass spectra of some aryl‐alkyl diethers
Authors: Vouros P. , Biemann K. 
Published: May 2005

AbstractThe mass spectra of catechol polymethylene diether homologs have been determined and the formation of unexpected fragment ions is reported. The size of the aliphatic ring significantly influences the relative intensity of the various ions produced. Possible mechanisms involving a ring contraction process are suggested to explain the formation of one of the common ion fragments (a) in the homologous series. Deuterium labeling experiments indicate that fragment ion a is formed by participation of the α carbons, but extensive isotope scrambling prevents the establishment of a concrete mechanism for the formation of the common catechol ion fragment (m/e 110).
On the loss of ammonia from phenylalkyl amines
Authors: Lightner D. A. , Sunderman F. W. , Hurtado L. , Thommen E. 
Published: May 2005

AbstractThe molecular ion‐minus‐ammonia [M – NHJ] fragmentation of (3‐phenylpropyl) primary amines is a major contributor to the total ion current. This fragmentation occurs to a lesser extent in the lower and higher homologs, (2‐phenethy1)‐ and (4‐phenylbuty1)amine. The loss of methylamine and dimethylamine from N‐methyl‐(3‐phenylpropyl)amine and N,N‐dimethyl‐(3‐phenylpropy1)amine respectively is essentially absent. Deuterium labeling has shown that C‐3 is the primary source of hydrogen abstracted in the [M  NHJ] fragmentation of (3‐pheny1propyl)amine.
The mass spectra of phenothiaphosphine derivatives
Authors: Granoth I. , Kalir A. , Pelah Z. , Bergmann E. D. 
Published: May 2005

AbstractThe molecular ion of the phenothiaphosphine derivatives is fairly stable. Under electronimpact, the phenothiaphosphines (I) and phenothiaphosphinic acids (IV, R = H) undergo a one‐step elimination of the phosphorus atom together with the groups attached to it. Substitutents in the aromatic rings, as well as on the phosphorus, influence the fragmentation pattern; ring methyl, e.g. leads to tropylium structures. Phosphine oxides of type V lose RO˙, probably after a rearrangement, when R = aryl, but R˙ if it is methyl.
Mass spectrometry of onium compounds—II. Carnitine and O‐acyl derivatives
Authors: Hvistendahl Georg , Undheim Kjell , Bremer Jon 
Published: May 2005

AbstractCarnitine and its O‐acyl derivatives undergo two major pyrolytic reactions in the mass spectrometer. Firstly elimination of water from carnitine or acid from acylcarnitine takes place followed by intramolecular displacement and formation of crotonyl lactone and trimethylamine. Secondly intramolecular displacement occurs with formation of a substituted γ‐lactone and trimethylamine. For the lower acid derivatives only the elimination pathway is important. For carnitine and higher derivatives both processes are important.The electron induced fragmentations of the major pyrolysis products are relatively simple. The most important pathways for the major components are discussed.The pyrolytic composition and mode of fragmentation are characteristic and can be used for identification purposes.
Benzyl vs. tropylium ions in the decomposition of some alkylnitrobenzenes
Authors: Westwood R. , Williams Dudley H. , Yeo Adrian N. H. 
Published: May 2005

AbstractThe [NO2C7H6]+ ions generated from m‐alkylnitrobenzenes have been shown to be different in their decomposition from those generated from p‐alkylnitrobenzenes, even when the alkyl group is methyl and the departing fragment a hydrogen radical. Thus, in these cases even molecular ions of relatively high internal energy do not reversibly ring‐expand to cycloheptatriene structures. In addition, the [NO2C7H6]+ ions, assumed to be benzylic, do not ring‐expand to nitrotropylium ions at internal energies sufficient to cause subsequent loss of NO or NO2 from the p‐ and m‐isomers, respectively.
Carbon skeletal rearrangement and hydrogen migration in thiophene
Authors: de Jong F. , Sinnige H. J. M. , Janssen Matthijs J. 
Published: May 2005

AbstractThe mass spectra of 13C‐labelled thiophenes were studied and the label‐distributions for the C3H3⊕, HCS⊕, C2H2S⊕ and [M  CH3]⊕ ions are interpreted in terms of a carbon skeletal rearrangement. From a comparison of the results of 13C‐labelling and D‐labelling, a concurrent hydrogen migration process is demonstrated. The production of HCS⊕ ions is preceded by partial carbon scrambling and hydrogen migration is of minor importance. In contrast, hydrogen scrambling predominates over carbon scrambling in the loss of acetylene.
Mass spectral fragmentation patterns of isomeric s‐Triazolo[4,3‐a]pyridines and s‐triazolo[1,5‐a]pyridines
Authors: Potts K. T. , Brugel E. , Singh U. P. 
Published: May 2005

AbstractThe major decomposition pathway involved in the fragmentation of derivatives of the title ring systems was the loss of RCN from the five‐membered ring, except when this ring had a 3‐amino,3‐hydroxyl or 3‐mercapto substituent. In these cases, the exocyclic substituent and at least one nitrogen atom from the five‐membered ring were lost.