bluuebunny/crossref_metadata_2025_split huggingface dataset:
Heterocyclic studies—XXX: Application of mass spectrometry to the study of covalent hydration
Authors: Clark Jim , Cunliffe A. E. 
Published: May 2005

AbstractComparison of the mass spectra of 3,4‐hydrated 4‐trifluoromethylpteridine derivatives with those of corresponding anhydrous compounds shows that this technique can be used to deduce the position of covalent hydration in heterocyclic compounds.It is less easy to demonstrate the presence of added water molecules in 5,6,7,8‐dihydrated derivatives of ethyl pteridine‐4‐carboxylates, but spectra run at low ionising voltages give the required information.Two hydrates (3,4‐hydrates of 4‐ethoxycarbonyl‐ and 4‐trifluoromethyl‐pteridine‐2(1H)‐thione) which are very much more thermally stable than usual are also discussed.Metastable peaks and accurate mass measurements support many of the postulated fragmentation pathways.
Mass spectrometry in structural and stereo‐chemical problems—CCXXIV: Fragmentation of cyclopropanes
Authors: Dias Jerry R. , Djerassi Carl 
Published: May 2005

AbstractGeneralizations for interpreting the mass spectra of cyclopropanes are enumerated and are based on the examination of many deuterium labeled substrates. Most cyclopropyl fragmentations can be visualized as resulting from ionization of the most substituted cyclopropyl bond in which the positive charge is localized on the most substituted carbon atom. Subsequent hydrogen shifts and/or simple scissions produce an array of predictable fragment ions.
The mass spectra of cyclo‐tripeptides of B‐alanine and 3‐amino‐3‐methyl butanoic acid
Authors: Drey C. N. C. , Lowbridge J. 
Published: May 2005

AbstractThe cyclo‐tripeptides of B‐alanine and of 3‐amino‐3‐methyl butanoic acid have been synthesised, the latter for the first time, and structures were confirmed by elemental analysis and mass spectrometry; accurate mass measurements showed that carbon monoxide was lost from the molecular ions; prominent peaks in the mass spectrum of both cyclic peptides are otherwise consistent with those reported for α‐peptides.
The mass spectra of methoxycycloalkanes and methoxymethoxycycloalkanes
Authors: Jones R. B. , Waight E. S. , Herz J. E. 
Published: May 2005

AbstractMass spectra of methoxycycloalkanes (CH3OR, R  C5 to C8) and of methoxymethoxycycloalkanes (CH3OCH2OR, R  C5 to C8, C12) have been compared with each other and with spectra of some steroidal analogues. It is concluded that the different fragmentation occurring in dimethoxymethane indicates decomposition before randomisation of excess energy.
Use of metastable peak shapes in determining ring size in cyclic rearrangements in the mass spectrometer
Authors: Beynon J. H. , Bertrand M. , Cooks R. G. 
Published: May 2005

AbstractA general method is described in which the mechanism of a reaction occurring in the ion source is inferred from the kinetic energy release accompanying further fragmentation of metastable product ions. In several cases the probe reaction occurred competitively by two mechanisms, and if high energy resolution is available this allows the detailed metastable peak shapes and not merely the average kinetic energy released, to be used to characterize the product ion formed in the fast (ion source) reaction. It is found that most substituted benzaldoxime O‐methyl ethers undergo HCN elimination via a five‐centered methoxyl transfer in the ion source, but that the p‐methoxy substituted compound reacts through both a four‐ and a five‐membered cyclic intermediate. The slow reactions of the corresponding metastable ions occur predominantly through a four‐centered transition state in the p‐methoxy compound and probably through both four‐ and five‐membered intermediates for the less strongly electron donating substituents. The fraction of the excess energy of the products is higher than expected from a consideration of energy partitioning data for other systems involving activated complexes of comparable tightness.
Elektronenstossinduzierte CH4‐Abspaltung aus dem Fragment [C7H9]+ von p‐Methyl‐1‐phenyläthanol‐1
Authors: Köppel Claus , Schwarz Helmut , Bohlmann Ferdinand 
Published: May 2005

AbstractHochauflösende Massenspektrometrie von 2H‐markierten Verbindung zeigt, dass das Ion [C7H9]+, das aus p‐Methyl‐(1)‐Phenyläthanol‐(1) durch Verlust von CH3· und CO gebildet wird, Methan bevorzugt aus einer Dreiringstruktur verliert. Andere Reaktionswege haben nur einen geringen Anteil an dieser Abspaltung.
A field ionization study of octan‐2‐one
Authors: Derrick P. J. , Falick A. M. , Lewis S. , Burlingame A. L. 
Published: May 2005

AbstractH/D randomization is not observed within the octan‐2‐one‐1,1,1,3,3‐d5 molecular ion at times less than 7 × 10−10 sec following field ionization. Partial H/D randomization is observbed at 10−6 to 10−5 sec. It is deduced that the curves of microscopic rate constant k against internal excitation energy E for the reactions effecting randomization and for the McLafferty rearrangement intersect. The field ionization kinetics (FIK) for the McLafferty rearrangement in octan‐2‐one‐1,1,1,3,3‐d5 are investigated over a time range extending from 10−11 to 10−6 sec. The maximum microscopic rate constant k for the reaction is estimated as 5 × 1010 sec−1. It is suggested that FIK measurements with a double focusing mass spectrometer be made by sweeping the blade potential rather than by the alternative technique of sweeping the electric sector analyzer potential. The ‘normnal’ FI mass spectra of octan‐2 one and octan‐2‐one and octan‐2‐one‐1,1,1,3,3‐d5 are presented and discussed. It is proposed that the m/e 56 species in the ‘normal’ FI mass spectrum of octan‐2‐one represents a doubly charged ion formed by loss of oxygen in a surface process.
Mass spectra of substituted 4,6‐bis‐aryl‐2‐pyrimidoles
Authors: Ivanovskaya L. Yu. , Gorfinkel M. I. , Sedova V. F. , Dubovenko Z. D. 
Published: May 2005

AbstractAn analysis of the mass spectra of 18 4,6‐bis‐aryl‐2‐pyrimidoles was performed. Regularities allowing structure determination, in particular for isomers, are discussed.
Mass spectra of trimethylsilyl ethers of some Δ5‐3β‐hydroxy C 19 steroids
Authors: Brooks C. J. W. , Harvey D. J. , Middleditch B. S. , Vouros P. 
Published: May 2005

AbstractThe mass spectra (20 eV electron energy) of a wide range of %Δ5‐3β‐hydroxy C19 steroid TMS ethers have been examined with the aid of high‐resolution mass measurements, together with deuterium and oxygen‐18 labelling data. The validity of many previously proposed fragmentation modes has been confirmed. A number of ions regarded as diagnostic have been shown to be less specific than had been formerly supposed. Several novel fragmentations have been observed and investigated.
Elektronenstossinduzierte fragmentierung von polymethylbenzaldehyden—II: Mechanismus der Methyl‐Abspaltung aus dem Molekül‐Ion von Tri‐ und Pentamethylbenzaldehyden
Authors: Schwarz Helmut , Bohlmann Ferdinand , Russ Barbara 
Published: May 2005

AbstractDie elektronenstossinduzierte Methyl‐Abspaltung aus Tri‐und Pentamethylbenzaldehyden kann durch eine vinyloge α‐Spaltung erklärt werden. Umlagerungen können ausgeschlossen werden.
The high resolution mass spectra of α,β‐unsaturated and α‐chloromercuri‐α,β‐unsaturated steroidal ketones
Authors: Smith Howard E. , Smith Roy G. 
Published: May 2005

AbstractThe high resolution mass spectra (500 eV) of some α,β‐unsaturated steroidal ketones have been studied and compared with the spectra of the corresponding α‐chloromercuri ketones. In the latter, the carbon‐mercury bond frequently remains intact at the expense of the fission of two carbon‐carbon bonds. The abundance of mercury‐containing ions allows the use of the mercury atom fingerprint in confirming ring B fragmentation of the steroid nucleus at C(6)–C(7) and C(9)–C(10) for 5α‐androst‐1‐ene‐3,17‐dione, 1,4‐androstadiene‐3,17‐dione and their 2‐chloromercuri derivatives; and at C(7)–C(8) and C(9)–C(10) for 1,4,6‐androstatriene‐3,17‐dione, 1,4,6‐androstarien‐17 β‐ol‐3‐one and their 2‐chloromercuri derivatives. 2‐Chloromercuri‐1,4,6‐androstatriene‐3,17‐dione and 2‐chloromercuri‐1,4,6‐androstatrien‐17 β‐ol‐3‐one also give an abundant ion as the result of ring C fragmentation at C(8)–C(14) and C(11)–C(12), the chloromercuri group being replaced by a hydrogen atom. This ring C cleavage gives the only recognizable distinctive fragmentation ion for 1,4,6‐pregnatriene‐3,20‐dione and 2‐chloromercuri‐1,4,6‐pregnatriene‐3,20‐dione. For most of the mercurated steroids, the low resolution mass spectra (70 eV) are reported. In these spectra, the fragmentation patterns are similar to those obtained using the higher ionization energy employed for the high resolution spectra.
Studies in organic mass spectrometry‐XIII: Investigation of electron‐induced isomerisation of αβ‐ and βγ‐unsaturated esters
Authors: Lauwers W. , Serum J. W. , Vandewalle M. 
Published: May 2005

AbstractThe mass spectral fragmentation of methyl esters of α,β‐ and β,γ‐unsaturated carboxylic acids has been studied. Deuterium labelling, metastable ion analysis and high resolution mass spectrometry have been utilised to elucidate the mechanism of a number of fragmentations and to check possible double bond migration prior to fragmentation. Some breakdown modes were found to occur through double bond migration. Additional support was provided by application of the ‘Metastable Ion Characteristics’ method. Partial isomerisation of molecular ions must therefore be accepted.
Octahedral metal carbonyls‐XXIX: Mass spectra of cis‐disubstituted derivatives of the group VI‐B metal carbonyls
Authors: Brown Richard A. , Paxson John R. , Dobson Gerard R. 
Published: May 2005

AbstractThe mass spectra of a number of cis‐disubstituted derivatives of the Group VI‐B metal carbonyls (M = Cr, Mo, W), in which the substituents are bidentate ligands bonding to the metal through As, S or N donor atoms, have been obtained. The spectra for derivatives of o‐phenylenebis‐(dimethylarsine) (diars) have been examined in greatest detail. For these latter complexes, competitive loss of carbonyls and diars methyl groups was observed. The proposed use of such competition in the evaluation of metal‐carbonyl bond strengths is examined. For complexes containing ethylene‐bridged bidentate ligands, ions indicative of the loss of five fragments of 28 mass units from the parent ion, corresponding to loss of four carbonyls and the ethylene bridge, are observed. The question of whether ethylene loss occurs prior to, competitively with or after carbonyl loss is considered.
Mass spectrometry of pyridine compounds–IV: The formation and decomposition of the [M – methyl]+ ion [C8H10N]+ from 4‐t‐butylpyridine in comparison with that of the [M – methyl]+ ion [C9H11]+ from t‐butylbenzene, as studied by D‐ and 13C‐labelling
Authors: Neeter R. , Nibbering N. M. M. 
Published: May 2005

AbstractA strong secondary isotope effect is observed in the preferred loss of methyl vs. trideutero‐methyl from the molecular ions of appropriately labelled 4‐t‐butylpyridine and t‐butylbenzene decomposing in the first and second field free regions of a double focusing mass spectrometer. This has been rationalised by invoking the theory of radiationless transitions2, which can account for the higher population of activated states responsible for loss of methyl vs. that for trideuteromethyl.13C‐Labelling at the central carbon atom of the t‐butyl group indicates that the [M – methyl]+ ions, decomposing further by elimination of ethylene, cannot be represented exclusively by a pyridylated (or phenylated) cyclopropane ion if present at all. It is concluded that ions with structures generated by 1,2‐hydrogen‐, 1,2‐pyridyl‐ (or 1,2‐phenyl‐) and 1,2‐methyl shifts must also play a role.D‐labelling further shows an extensive randomisation of side‐chain hydrogen atoms in the [M‐methyl]+ ions of 4‐t‐butylbenzene; in this case, however, the expelled ethylene also contains ring hydrogen atoms (≤2). Presumably this is caused by exchange between the side‐chain and ortho‐hydrogen atoms in the initially generated phenyldimethylcarbinyl carbenium ion.
Field desorption mass spectra of stereoisomeric glycosides
Authors: Lehmann W. D. , Schulten H.‐R. , Beckey H. D. 
Published: May 2005

AbstractField desorption mass spectrometry (FD‐MS) yields differentiated spectra for unshielded α‐ and β‐stereoisomeric glycosides. The small but characteristic differences enable a distinction to be made between the two isomers. Valuable structural information can be deduced from the simple cleavage between the sugar moiety of the molecule and the aglycon. A short comparison with electron‐impact (EI) and field ionisation (FI) spectra is given.
An experimental and indo molecular orbital study of variable response of the p‐phenyl substituent to electron demand. Relative conformations of two p‐arylacetophenones as neutral molecules and +1 molecular ions
Authors: Twine Charles E. , Parker Carol E. , Bursey Maurice M. 
Published: May 2005

AbstractThe INDO molecular orbital method suggests that the rings of p‐phenylacetophenone and 2‐fluoro‐4′‐acetylbiphenyl are more nearly coplanar in the +1 molecular ion than in the neutral molecule. This is indicated by old experimental data for the former and new data for the latter, based on the cleavage to [CH3CO]+.
The ortho effect in mass spectra. Insight into the tightening of activated complexes for the loss of ketene from phenyl acetates and ethylene from phenetoles from INDO molecular orbital calculations
Authors: Parker Carol E. , Hass J. Ronald , Bursey Maurice M. , Pedersen Lee G. 
Published: May 2005

AbstractINDO Molecular orbital calculations of the energetically most favourable conformation of the molecular ions of phenyl acetate and its o‐fluoro‐ and o‐chloro‐analogs indicate bond formation between carbonyl oxygen and ortho halogen. For the molecular ions of phenetole and its o‐fluoro and o‐chloro‐analogs, no ring formation is observed. These results are in accord with the frequency factor changes found for the ortho substitution in these systems by halogens.
Mass spectral studies of some complexes of niobium(V) and tantalum(V) with chloro, alkoxy, acetylacetonato or salicylaldehydato ligands
Authors: Stefanović D. , Stambolija Lj. , Katović V. 
Published: May 2005

AbstractMass spectra of complex compounds of niobium (V) and tantalum (V) of the type MCl2(OR)2L have been measured, where M = Nb and Ta; HL = 2,4‐pentanedione, R = CH3, C2H5 and HL = Salicyladehyde, R = CH3. The fragmentation upon electron‐impact depends on the nature of the ligands and to a minor extent on the central metal atom. A fragmentation scheme has been constructed on the basis of measurements of metastable transitions and accurate masses of important fragment ions. Rearrangement reactions involving hydrogen migration among ligands have been observed.
Internal energy effects on metastable characteristics. The structure of [C3H7O]+ ions
Authors: Tsang C. W. , Harrison A. G. 
Published: May 2005

AbstractThe effect of changes in the internal energy distribution of the fragmenting ion on the ratio of metastable ion intensities for two competing fragmentation reactions has been investigated both theoretically and experimentally. Model calculations have shown that if the competing reactions have significantly different activation energies the metastable intensity ratio does depend on the internal energy distribution although large changes are necessary before the ratio changes by more than a factor of two. Experimentally the metastable characteristics of [C3H7O]+ ions of nominal structures [CH3CH2O+CH2] (I), [(CH3)2CO+H] (II), [CH3CH2CHO+H] (III) and [CH3O+CHCH3] (IV) have been examined. For each structure the metastable characteristics are found to be distinctive and independent of changes in the internal energy distribution of the fragmenting ion where these changes result from altering the precursor of the [C3H7O]+ ions. It is suggested that these internal energy changes can be estimated from the fraction of [C3H7O]+ ions which fragment in the ion‐source. It is concluded that structures I to IV represent stable and distinct ionic structures.
Silylgruppenwanderung und CO2‐Eliminierung beim massenspektrometrischen Zerfall von N‐Trifluoracetyl‐α‐aminosäretrimethylsilylestern
Authors: Birkoffer L. , Schmidtberg G. 
Published: May 2005

AbstractDie Molekü‐Ionen der N‐Trifluoracetyl‐α‐amminosäuretrimethylsilyester zeigen im Gegensatz zu anderen Aminosäurederivaten eine charakteristische Abspaltung von CO2, offensichtlich als Folge einer Wanderung der Ester‐trimethylsilylgruppe zum Sauerstoff der N‐Trifluoracetylfunktion. Durch die weitere Fragmentierung der so gebildeten [M‐CO2]+˙‐Ionen entstehen besonders bei Derivaten der aliphatischen Aminosäuren intensive Bruchstü ke. Bei den Isomeren leucin und Isoleucin führt sie sogar zu unterschiedlichen basispeaks für die 20 eV‐Spektren. Aminosäuren mit leicht abspaltbarer gruppe in β‐Position scheinen Co2 synochron mit dieser Gruppe zu eliminieren, so daß bei ihnen das [M‐CO2]+˙‐Ion selbst nicht zu beobachten ist. Als Konkurrenzreaktion zur Wanserung der estersilylgruppe zum N‐Triffuoracetyl‐sauerstoff tritt bei Serin, Threonin und Cystein eine Si‐Umlagerung zur β‐ständigen funktionellen Gruppe auf. Auch sie verläuft unter gleichzeitiger Abspaltung von CO2.
The benzoyl cation: The participation of isolated electronic excited states in the dissociation of molecular ions of the form [C6H5COX]+˙
Authors: Benoit F. 
Published: May 2005

AbstractThe heat of formation of the benzoyl cation generated from [C6H5COX]+˙ is found to depend on X, while the heat of formation of the phenyl ion produced therefrom is, with one exception, independent of X. The excess energy of the benzoyl cation can be accounted for by an electronic excited state of the ion in the mass spectra of benzoic acid, benzaldehyde, benzamide, methyl benzoate and possibly benzophenone; the benzoyl cation is not excited in the mass spectra of acetophenone and benzoyl chloride.
Mass spectral studies on 7‐azabicyclo (2.2.1) heptane systems
Authors: Das K. G. , Kulkarni P. S. , Roy S. K. 
Published: May 2005

AbstractAn attempt has been made to rationalise the major fragmentation modes of a few C2, C3 disubstituted 7‐p‐toluene sulphonyl and 7‐carbobenzyloxy‐7‐azabicyclo (2.2.1) heptanes.
Field ionisation mass spectrometry of acetylpyridine isomers
Authors: Migahed M. D. , Hetal A. I. , El‐Kholy S. B. 
Published: May 2005

AbstractAn investigation of the metastable transition in the field ionisation mass spectra of acetylpyridine isomers has established that the reaction pathway is greatly influenced by the ring position of the substituent. It is suggested that the pyridine nitrogen atom induces a rearrangement process in the case of 2‐acetylpyridine. In other acetylpyridines it has a little effect and the cleavage reaction occured prior to rearrangement.
The mass spectra of some pyridazines, pyrido‐pyridazines and related compounds
Authors: Kramer V. , Medved M. , Stanovnik B. , Tišler M. 
Published: May 2005

AbstractThe mass spectral fragmentation behaviour of substituted sulphur containing pyridazines, pyrido (2,3‐d) pyridazines and pyrido‐thiazolo‐pyridazines has been investigated and fragmentation patterns proposed.
Using model ionization efficiency curves to evaluate the methods for determining appearance potentials
Authors: Occolowitz J. L. , Cerimele B. J. , Brown Peter 
Published: May 2005

AbstractSix methods of estimating appearance potentials from ionization efficiency curves of ions arising from single, competitive, consecutive and isolated ionic reactions are evaluated, using computed electron‐impact ionization efficiency curves as ‘experimental’ data.Of the linear extrapolation, semi‐log, second derivative, energy compensation, Warren and critical slope methods, a modified critical slope method gives the most accurate appearance potentials for fragment ions. Experimental data are presented to support this conclusion.
Photoionisation and fragmentation of the stereoisomers of 4‐t‐butylcyclohexyl acetate and 4‐t‐butylcyclohexyl methyl ether
Authors: Akhtar Zinat M. , Brion C. E. , Hall L. D. 
Published: May 2005

AbstractThe fragmentation of the stereoisomers of 4‐t‐butylcyclohexyl acetate and 4‐t‐butylcyclohexyl methyl ether has been studied by photoionisation mass spectrometry at 1216 Å and 584 Å. Deuterium substitution and high resolution mass spectrometry have been used to gain further insight into the fragmentation pathways.
Mass spectrometry of the trimethylsilyl derivatives of medicinal barbiturates
Authors: Falkner Fred C. , Throck watson J. 
Published: May 2005

AbstractThe electron ionization mass spectra of the trimethylsilyl derivatives of a number of medicinal barbiturates have been examined. The trimethylsilyl derivatives are useful in the identification of barbiturates by gas liquid chromatography/mass spectrometry (g.l.c.‐m.s.). Mass spectra of these derivatives are characterized by abundant high mass ions which permit the ready distinction of one barbiturate from another. The prominent and characteristic [M ‐ 15] ion is an effective monitor of molecular weight, while other unique fragmentations and/or varying patterns of relative abundance serve to differentiate isomers.
The rational use of a dynamic on‐line data processing system for high and low resolution mass spectrometry
Authors: Van 'T Klooster H. A. , Vaarkamp‐Lijnse J. S. , Dijkstra G. 
Published: May 2005

AbstractSome of the factors determining the configuration of a mass spectrometry data processing system are discussed. A rationalisation is given for a laboratory situation dealing with a variety of mass spectrometric problems. The effective use of a dynamic on‐line system in such an environment is demonstrated. Conversational procedures are described for the acquisition, reduction and interpretation of mass spectral data, using a CRT visual display terminal as a fast man‐computer interactive communication medium.
Conformations of highly hindered aryl ethers. XXI—fragementation paths involving intramolecular π‐complexes and cyclizations in the mass spectra of 2,4‐dinitrophenyl 2′‐alkylphenyl ethers
Authors: Jáuregui J. Fernando , Lehmann F. Pedro A. 
Published: May 2005

AbstractThe mass spectrometric study of 2,4‐dinitrophenyl 2′‐R‐phenyl ethers (R  H, Me, Et, i‐Pr, tert‐Bu) showed that (1) fragmentation proceeds differently from unsubstituted and 4‐nitro‐substituted diphenyl ethers; (2) important fragmentation routes involve interannular migrations and cyclizations; (3) these occur between two groups ortho to the ether linkage while the ethers are in unfavorable endo, endo twist conformations; (4) the observed interannular interactions can be ustified by the existence in these compounds of an intramolecular π‐complex which stabilizes the sterically unfavorable conformation and explains the observed fragmentations.
Mass spectrometry in structural and stereochemical problems. CCXXXVII—Electron‐impact‐induced hydrogen losses and migrations in some aromatic amides
Authors: Duffield A. M. , DeMartino G. , Djerassi Carl 
Published: May 2005

AbstractThe mass spectra of a series of benzamides and naphthamides have been investigated with respect to their propensity to lose an aromatic hydrogen atom from their molecular ions. Deuterium labeling and a study of model compounds have led to a plausible mechanistic rationalization for the formation of the [M — 1] ions. The other principal fragmentation processes observed with these compounds are discussed, including the specificity of a previously uninvestigated rearrangement process.
Mechanisms of mass spectrometric fragmentations: X–Interaction between remote or‐groups in decalin‐1,5‐diols and their dimethyl ethers
Authors: Grützmacher Hans‐Friedrich , Fechner Karl‐Heinz 
Published: May 2005

AbstractThe mass spectra of the five stereoisomers of decalin‐1,5‐diol and its dimethyl ether have been investigated. The differences in the mass spectra of stereoisomers I to III with a trans‐ decalin ting system are small. The differences are much larger in the mass spectra of the two isomers IV and V of the cis‐decalin series and the elimination of CH2O, formed by interaction between the two methoxy groups, from the molecular ion is only observed in the mass spectrum of Vb.