bluuebunny/crossref_metadata_2025_split huggingface dataset:
Mass spectrometric studies of dithiophosphinato metal complexes
Authors: Heinz S. , Keck H. , Kuchen W. 
Published: May 2005

AbstractElectron impact induced fragmentation reactions of planar, tetrahedral, octahedral and oligomeric metal dithiophosphinates Me(II)L2 (L=Et2PS2−; Me(II)=Zn, Cd, Hg, Pb, Co, Mn, Ni, Pd, Pt), Me(III)L3 (Me(III) = Sb, Bi, In, Rh, Ir) and (Me(I)I)n (Me(I)/n=Tl/1, Au/2, Cu/4) have been studied. Fragmentation patterns, which are in accordance with metastable peak determinations by linked scans, are reported. In the case of the transition metals the spectra of the complexes show abundant [M]+· predominantly metal containing ions and, the former being weak and the intensities of the latter being considerably reduced in the case of metal complexes with filled d shells. With planar or tetrahedral transition metal complexes no dependence of fragmentation on the coordination geometry can be observed. The dependence of fragmentation on d configuration, ionization energy of the metal and metal ligand π bonding is discussed. In the case of the oligomeric complexes strong metal‐metal interaction is observed even under electron impact.
Comparison of ‘soft ionization’ techniques with electron impact mass spectrometry for desoxinojirimycin and folic acid derivatives
Authors: Wünsche C. , Benninghoven A. , Eicke A. , Heinen H.‐J. , Ritter H. P. , Taylor L. C. E. , Veith J. 
Published: May 2005

AbstractSeven desoxinojirimycin and three folic acid derivatives were investigated using the soft ionization techniques of desorption chemical ionization (DCI), laser desorption (LAMMA), field desorption (FD), secondary ion mass spectrometry (SIMS) and fast atom bombardment (FAB). The mass spectra were compared with electron impact (EI) spectra and interpreted in terms of their suitability for analytical purposes.
The reactions of metastable [C5 H10 O]+˙ ions with the oxygen on the second carbon
Authors: McAdoo David J. , Hudson Charles E. , McLafferty Fred W. , Parks Terry E. 
Published: May 2005

AbstractNearly all [C5H10O]+˙ isomers with the oxygen on the second carbon are shown to interconvert with each other and lose methyl and ethylene at the threshold for dissociation. The methyls contain the carbons from the 1‐ and 5‐positions with about equal frequency, and C(3) or perhaps C(4) about half as often as either terminal carbon. CH3 CH2 CH2 CO+ is formed by loss of the C(1) methyl and magnified image by loss of the C(5) methyl. Hydorgen transfer between C(5) and the oxygen and between the oxygen and C(4) are facile, and 1,2‐hydrogen transfers between C(3) and C(4) occur with high frequency. Extensive skeletal rearrangements also take placae by 1,2‐shifts between C(2), C(3) and C(4). We attribute the occurrence of teh three‐center shifts between C(2), C(3) and C(4) to the presence of considerable charge density on C(2) and C(3) in many of the [C5H10O]+˙ isomers. The isomerizations of [C5H10O]+˙ can be considered a mixture of free radical and carbocation reactions. Strong similarities exist between the isomerizations of metastable [C5H10O]+˙ ions with the oxygen on the second carbon and those of isomers of ionized butanoic acid, methyl butanoate and n‐butanal.
LAMMA mass spectra of β‐diketone, bis(benzoylacetone)ethylenediimine and bis(salicylidene)ethylenediimine complexes of some transition metals
Authors: Rohly Kenneth E. , Heffren John S. , Douglas Bodie E. 
Published: May 2005

AbstractComplexes of 2,4‐pentanedione (acetylacetone, acac), [Cu(acac)2], [VO(acac)2] and [CO(acac)3], and the chromium(III) derivative of 3‐methyl‐2,4‐pentanedione (methylacetylacetone, meac), [Cr(meac)3], the ligands bis(benzoylacetone)ethylenediimine and bis(salicylidene)ethylenediimine, and their cobalt(II), nickel(II) and copper(II) chelates were analysed by laser desorption mass spectrometry (LAMMA) and compared to electron impact (EI) results. The positive ion LAMMA spectra generally reveal mostly small fragments, although metal cationization peaks are seen for most complexes. Negative ion LAMMA produce carbon clusters and some structurally important fragments.
Doubly charged ion mass spectra 8—alkenes
Authors: Appling J. R. , Musier K. M. , Moran T. F. 
Published: May 2005

AbstractDoubly charged ion mass spectra of 23 alkenes have been measured using a double focusing Hitachi RMU‐7L mass spectrometer. Ion mass spectra were obtained using 100 eV electron energy and 3.2 kV ion accelerating voltage. Each 2E spectrum was determined using the olefinic compound under investigation as the target gas. In general, spectra are dominated by fragment ions which result from extensive hydrogen loss from the doubly charged molecular ion. Appearnce energies have been measured for intense fragment ions in each spectrum.
Ion–molecule reaction in the gas phase 4—Stereospecific nucleophilic substitution under ammonia chemical ionization conditions from diastereomeric methyl and benzyl ethers of 3‐hydroxy steroids
Authors: Tabet Jean‐Claude , Tondeur Yves , Hirano Yutaka , Wegmann Annemarie , Tecon Pierre , Djerassi Carl 
Published: May 2005

AbstractThe ammonia chemical ionization (CI/[NH4+]) mass spectra of a series of diastereomeric methyl and benzyl ethers derived from 3‐hydroxy steroids (unsaturated in position 5 and saturated) have been studied. The adduct ions [M+NH4]+ and [MH]+ and the substitution product ions [M+NH4ROH]+ (thereafter called [MsH]+) are characterized by an inversion in their relative stabilites in relation to their initial configuration. [M+NH4]α+ and [MH]α+ formed from the α‐Δ5‐steroid isomers are stabilized by the presence of a hydrogen bond which is not possible for the β‐isomers. This stereochemical effect has also been observed in the mass analysed ion kinetic energy (MIKE) spectra of [M+NH4]+ and [MH]+. The MIKE spectra of [MsH]+ indicate that those issued from the β‐isomers are more stable than the one originating from the α‐isomers. This behavior is also observed in the first field free region (HV scan spectra) for [MH]+, [MsH]+ and [M+NH4]+ which are precursors of the ethylenic carbocations (base peak in the conventional CI/[NH4]+ spectra). Mechanisms, such as SN1 and SNi, have been ruled out for the formation of [MsH]+, but instead the data support an SN2 mechanism during the ion‐molecule reaction between [M+NH4]+ and NH3.
Mechanisms of ion formation in field desorption of oligosaccharides
Authors: Rogers David E. C. , Derrick Peter J. 
Published: May 2005

AbstractEnergy deficits have been measured for ions in the field desorption mass spectra of saccharides. Evidence is presented to show that monosaccharides, disaccharides and trisaccharides are volatile compounds, under the conditions of field desorption. It is proposed that the electric field plays an essential role in the desorption of [M+H]+ ions.
Mass spectral fragmentation pathways in 2,4,6‐trinitrotoluene derived from a MS/MS unimolecular and collisionally activated dissociation study
Authors: Robert Carper W. , Cameron Dorey R. , Tomer Kenneth B. , Crow Frank W. 
Published: May 2005

AbstractThe fragmentation pathways of 2,4,6‐trinitrotoluene have been examined using 15N and 2H isotopic labelling in conjunction with tandem mass spectrometry. Both the unimolecular and collisionally activated decomposition modes were investigated. Fragmentation pathways were established in both modes and isotopic shifts were used to determine the groups lost. The major pathways include the loss of OH or H2O, followed by the subsequent loss of NO or NO2. There is virtually no ring disintegration until the majority of the attached groups are lost.
Rearrangements and isomerism in the molecular ion of o‐methoxybenzoic acid
Authors: Gillis Richard G. , Porter Quentin N. 
Published: May 2005

AbstractThe molecular ion of o‐methoxy‐d3‐benzoic acid can undergo three different rearrangements and hydrogen/deuterium exchange between the functional groups. This can result in 14 isomers of the molecular ion before it decomposes giving fragments at m/z 105, 106, 107 and 108. Three types of isomer have been identified.
Mass spectroscopic fragmentation pathways of 1,8‐nonadiyne
Authors: Robbins Ronny Charles , Foster Norman George 
Published: May 2005

AbstractCleavage α to triple bonds in straight‐chain hydrocabons with only one triple bond is a very minor process. The mass spectrum of 1,8‐nonadiyne (mol. wt 120) shows strong peaks at around m/z91, which points to a major fragmentation pathway of cleavage α to triple bonds in straight‐chain diynes. This study attempts to explain this paradox. Through‐space interaction was indicated through the use of carbon‐13 labelling of the terminal carbon atoms in 1,8‐nonadiyne, 1,2,8,9‐13C‐1,8‐Nonadiyne and 3,7‐13C‐1,8‐nonadiyne were prepared to determine which carbon atoms were lost in the process of [M]+˙ and [M1]+ going to m/z91. These two molecules were chosen for ease of synthesis. Low‐resolution mass spectra and low‐voltage studies determined that a major portion of carbon atoms being lost were from the middle of the carbon chain. This points to a fragmentation pathway that results from through‐space interaction of the two terminal triple bonds. It is likely that ionization enhances this through‐space interaction of the two triple bonds.
Three new isomers of [C2H6O]+˙: The radical cations [CH3O(H)CH2]+˙, [CH3CHOH2]+˙ and a low‐energy isomer of unassigned structure
Authors: Burgers Peter C. , Holmes John L. , Terlouw Johan K. , van Baar Ben 
Published: May 2005

AbstractThree new [C2H6O]+˙ ions have been generated in the gas phase by appropriate dissociative ionizations and characterized by means of their metastable and collisionally induced fragmentations. The heats of formation, ΔHf0, of the two ions which were assigned the structures [CH3O(H)CH2]+˙ and [CH3CHOH2]+˙ could not be measured. The third isomer, to which the structure \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm CH}_{\rm 2} = \mathop {\rm C}\limits^{\rm .} {\rm H} \cdot \cdot \cdot \mathop {\rm H}\limits^ + \cdot \cdot \cdot {\rm OH}_{\rm 2} $\end{document} is tentatively assigned, was measured to have ΔHf0 = 732±5 kJ mol−1, making it the [C2H6O]+˙ isomer of lowest experimental heat of formation. It was found that the exothermic ion–radical recombinations [CH2OH]++CH3˙→[CH3O(H)CH2]+˙ and \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm CH}_{\rm 3} \mathop {\rm C}\limits^{\rm + } {\rm HOH + H}^{\rm .} $\end{document}→[CH3CHOH2]+˙ have large energy barriers, 1.4 and ⩾0.9 eV, respectively, whereas the recombinations yielding [CH3CH2OH]+˙ have little or none.
Optimization of operating conditions for desorption chemical ionization mass spectrometry
Authors: Takeda Naohito , Harada Ken‐ichi , Suzuki Makoto , Tatematsu Akira 
Published: May 2005

AbstractOptimization of the operating conditions for desorption chemical ionization (D/CI) mass spectrometry has been evaluated on the production of molecular ion species as well as structurally informative fragment ion species with sucrose as a main model compound. Among various parameters examined, it was found that configuration and heating rate of the emitter wire were significantly concerned with the desorption efficiency, while chamber temperature played an important role on the control of the fragmentation process rather than the desorption process. Therefore, the conditions for optimal molecular ion species are quite opposed to those for optimal fragment ion species. The former can be achieved by the use of the highest heating rate combined with the lowest chamber temperature. Under the optimal operating conditions, a 20 ng sample of sucrose is adequate for recording a clear mass spectrum with good reproducibility, where [M·NH4]+ (m/z 360) is the base peak and the glycosyl ion [S·NH3]+ (m/z 180) also has moderate abundance (rel. int., 40%).
Structure of gas phase [C5H6]+˙ ions
Authors: Flammang Robert , Meyrant Philippe , Maquestiau André , Kingston Eric E. , Beynon John H. 
Published: May 2005

AbstractCharge‐stripping spectra have been used to differentiate ionized cyclopentadiene from its acyclic isomers. The minimum amounts of translational energy lost during the charge‐stripping processes and the relative charge‐stripping efficiencies, which are also structurally important parameters, have been measured for these ionic species. [C5H6]+˙ ions, formed by dissociative ionization of various precursors in the ion source are found, usually, to be a mixture of cyclic and acyclic ions. In contrast, [C5H6]+˙ ions, derived from the dissociation of metastable molecular ions from a series of organic compounds, have the cyclopentadienyl structure. This structure was confirmed by collision‐induced dissociation of ions formed in the first field‐free region of a triple sector mass spectrometer.
The Claisen rearrangement of protonated allyl phenyl ether
Authors: Kingston Eric E. , Beynon John H. , Liehr Joachim G. , Meyrant Philippe , Flammang Robert , Maquestiau André 
Published: May 2005

AbstractMolecular protonated ions of allyl phenyl ether undergo a Claisen rearrangement both in the ion source and along the flight path. The rearranged ions undergo fragmentation, the predominat loss being ethene, and only a small contribution from loss of carbon monoxide is observed. Collision‐induced dissociation spectra are used to verify the structures of the daughter ions. These spectra, together with other evidence of an acid‐induced ortho rearrangement, allow a mechanism to be proposed for the ethene loss. In contrast, molecular protonated ions of propargyl phenyl ether lose exclusively carbon monoxide.
Selective reagents in chemical ionization mass spectrometry: Tetramethylsilane
Authors: Clemens David , Munson Burnaby 
Published: May 2005

AbstractMixtures of 50% tetramethylsilane (TMS) and methane have been found to give [M+73]+ adduct ions and structurally useful fragment ions for many oxygen‐ and nitrogen‐containing organic compounds. All of the reagent ions in TMS react with polar compounds. The high‐pressure TMS chemical ionization spectra of many simple oxygenated compounds are in agreement with predictions from ion chemistry of (CH3)3Si+ obtained by ion cyclotron resonance experiments at very low pressures, but differences are noted. Sensitivities for oxygen‐, nitrogen‐, and sulfur‐containing compounds with TMS as the reagent gas appear to be approximately the same.
Electron impact induced ortho effects in 2‐nitro‐substituted aromatic sulphides containing 2‐pyridyl, 2‐(5‐methylthio‐1,3,4‐thiadiazolyl) and/or 2‐(4‐methyl‐1,3,4‐thiadiazolinyl‐5‐thione) moieties
Authors: Pappalardo Sebastiano , Di Grazia Michele 
Published: May 2005

AbstractThe most significant mass spectral features of 14 title compounds are discussed with the aid of deuterium labelling experiments. The decomposition patterns of these compounds are strongly affected by several competing ortho effects, due to the interaction of the nitro function(s) with neighbouring electron‐poor N‐heterocycles. Very intense polycyclic ions are produced via addition‐elimination reactions by loss of simple radicals (H˙, OH˙, NO2˙) from the molecular ion, followed by the ejection of neutral molecules (HNO2,CH3SCN or CH3NCS). In addition, primary or secondary intramolecular oxygen transfers, preceded or not by hydrogen migration, from the nitro group to the imino carbon via spirocyclic intermediates, are generally observed. Minor skeletal rearrangements, triggered by single or multiple intramolecular oxygen transfer to the bridgehead sulphur atom, followed by SO or SO2 ejection, are also noticed.
Mass spectrometric study on 2‐amino‐as‐triazino[6,5‐c]quinoline and some of its derivatives
Authors: Vékey K. , Tamás J. , Berényi E. , Benkó P. 
Published: May 2005

AbstractElectron impact induced fragmentations of 2‐amino‐as‐triazino[6,5‐c]quinoline and its 2‐methylamino, 2‐dimethylamino and 2‐benzylamino analogues have been investigated. The main primary decomposition route of both the singly and the doubly charged molecular ions is the N2 loss. For the singly charged ions the critical energy of this reaction is 110±10 kJ mol−1 and the kinetic energy release is 61±4 kJ mol−1. For the doubly charged ions these values are 90±10 kJ mol−1 and 5±2 kJ mol−1, respectively, indicating a significantly different reaction profile. The further fragmentation of [MN2]+˙ ions consists of radical eliminations from the 2‐amino group with cleavages of the α‐ and β‐bonds. Here a significant substituent effect is eliminations found suggesting an intramolecular cyclization reaction with a substituent migration. D and 15N labelling experiments have shown a minor extent of randomization of the labelled atoms and the occurrence of other hidden skeletal rearrangements during the fragmentation.
Matrix effects in fast atom bombardment mass spectrometry of cationic iridium(III) and rhodium(III) coordination complexes
Authors: Divisia‐Blohorn B. , Kyriakakou G. , Ulrich J. 
Published: May 2005

AbstractFast atom bombardment mass spectra of cationic iridium(III) and rhodium(III) coordination complexes (M+Cl2L2, X−; where the ligand L is a dinitrogenous aromatic system) have been obtained with thioglycerol, glycerol or tetraglyme as a matrix. Two kinds of reactions, initiated by particle bombardment, have been discovered between these complexes and the matrix. First, with thioglycerol one or two chlorine atoms are substituted by a thioglycerol radical, more rapidly for rhodium compounds; secondly, when the ligand L possesses a diazo function, this function is hydrogenated depending on the ability of the matrix to generate hydrogen radicals by bombardment.
Chemical ionization mass spectrometry of derivatives of L‐dopa and L‐tryptophan and their detection in tumour samples
Authors: Duarte M. F. N. , Hutchinson D. W. , Jennings K. R. 
Published: May 2005

AbstractConditions have been established for the detection by chemical ionization mass spectrometry (CIMS) of compounds related to L‐dopa (3‐hydroxy‐L‐tyrosine) and L‐tryptophan without derivatization. The least fragmentation of the parent ion occurs in positive ion CIMS when methylamine is used as reagent gas. The compounds can also be detected by negative ion CIMS using carbon tetrachloride as reagent gas. While the total ion current in the latter technique is lower than that obtained with positive ion CIMS, the background noise in the mass spectra of samples obtained from natural sources is greatly reduced. CIMS has been used to show the presence of aromatic amino acids in acid extracts of samples of two different classes of tumour without sample derivatization.
Gas phase reactions of protonated 1,3‐diphenylpropyne and some isomeric [C15H13]+ ions
Authors: Bäther Wolfgang , Kuck Dietmar , Grützmacher Hans‐Fr. 
Published: May 2005

AbstractMetastable (3‐phenyl‐2‐propynyl)benzenium ions, generated by electron impact induced fragmentation from the appropriately substituted 1,4‐dihydrobenzoic acid, react by loss of ˙CH3 and C6H6. The study of deuterated derivatives reveals that hydrogen/deuterium exchanges involving all hydrogen and deuterium atoms precede the fragmentations. The results suggest a skeletal rearrangement by electrophilic ring‐closure reactions giving rise to protonated phenylindene and protonated 9,10‐methano‐9,10‐dihydroanthracene prior to the elimination of C6H6 and ˙CH3, respectively. A study of isomeric [C15H13]+ ions by collision‐induced decomposition and by deuterium labelling shows that these ions interconvert by hydrogen migrations and skeletal rearrangements.
Structural investigation of the antibiotic sporaviridin: 11—Molecular secondary ion mass spectral studies on the constituent pentasaccharides viridopentaoses
Authors: Harada Ken‐ichi , Kimura Ikumi , Masuda Katsuyoshi , Suzuki Makota 
Published: May 2005

AbstractMolecular secondary ion mass spectra of three pentasaccharides, viridopentaoses A, B and C, using various matrices, are discussed. The appearance of the molecular ion species is dependent upon the relative proton affinities between the sample and the organic matrix material. However, the presence of sodium ion, rather than proton, also greatly influences the appearance of the molecular ion species. The glycosidic linkages are mainly cleaved between the glycosidic oxygen atom and the anomeric carbon atom to give informative sugar sequence ions. These fragmentations have been confirmed by the linked scanning technique (B/E).
Amidine mass spectral fragmentation patterns
Authors: Barker James , Jones Michael , Kilner Melvyn 
Published: May 2005

AbstractElectron impact mass spectrometry of a range of amidines (R′NC(R)NHR′) including formamidines, acetamidines, benzamidines and tert‐butylamidine, has been undertaken, and comparisons made of the fragmentation pathways followed by the different families of compounds. Fragmentation of all the molecular ions is characterized by skeletal carbon‐nitrogen bond cleavage to form [R′NCR]+ and [R′NH]+ fragments, both of which are observed. For formamidines (RH), the positive charge remains with the [R′NH]+ fragment which leads to the base peak at m/z93 corresponding to [R′NH2]+˙. In contrast, for acetamidines and benzamidines the charge prefers to remain with the [R′NCR]+ fragment which gives the base peak for these compounds. The spectra of unsubstituted amidines (HNC(R)NH2) are characterized by cleavage of the carbon substituent from the NCN skeleton, [CN2H3]+ (m/z 43) being produced in all cases.
Bifunctional even‐electron ions: 1—Fragmentation behaviour of ω‐methoxy‐, ω‐hydroxy‐ and ω‐chloro‐oxonium ions
Authors: Záhorszky U. I. 
Published: May 2005

AbstractBifunctional oxonium ions—generated from tertiary aliphatic alcohols containing an additional hydroxy, methoxy or chloro group at the end of an alkyl side‐chain—do not markedly exhibit fragmentations typical of ordinary oxonium ions, but show as the main reactions those caused by functional group interaction, through‐space interaction being the dominant factor. The main primary fragmentation is loss of the additional functional group X as HX, followed by loss of the side‐chain originally separating the two functional groups, leading to carbonyl cations. This typical reaction sequence is initiated by proton migration from the oxonium moiety to the additional functional group. The reaction behaviour of the bifunctional ions is discussed. The lowest homologues show specific deviations from the general fragmentation behaviour.
The [C5H8]+˙ radical cation: Structural studies by energy‐resolved mass spectrometry
Authors: Mason R. S. , Jennings K. R. , Verma S. , Cooks R. G. 
Published: May 2005

AbstractControl of the degree of collisional excitation of an ion can be achieved by varying the collision energy or the number of collisions. The former experiment yields a series of daughter spectra which is analogous to a breakdown curve and which serves to characterize the ion undergoing collisionally activated dissociation (CAD). Recognition of differences in the spectra between isomeric ions is facilitated if the curves obtained from the energy‐resolved data are considered in pairs and their differences are plotted. This procedure serves to demonstrate that ionized 1,3‐ and 1,4‐pentadiene are structurally distinct, even though they are not distinguishable in conventional CAD. 2‐Pentyne and 3‐octyne give [C5H8]+˙ fragment ions which are closely related to the 1,3‐ and 1,4‐pentadiene structures, respectively. Any particular ion can be characterized by another form of difference spectrum: one comparing data at two collision pressures each taken over a range of collision energies. This procedure yields conclusions regarding ion structure which match those reached from the energy‐resolved experiments.