bluuebunny/crossref_metadata_2025 huggingface dataset:
Atmospheric pressure chemical ionization negative mass spectra of the dinitrotoluene isomers
Authors: Asselin Michel J. F. , Paré Jocelyn J. R.
Published: May 2005

The atmospheric pressure chemical ionization of the dinitrotoluene isomers in ambient air was studied with a quadrupole mass spectrometer operating in the negative mode. The isomers can be grouped on the basis of the product ions: 2,5‐, and 2,6‐ and 3,5‐dinitrotoluene give the molecular anion with little fragmentation; 2,3‐ and the 3,4‐dinitrotoluene behave similarly but with more extensive fragmentation; 2,4‐dinitrotoluene gives the quasimolecular [DNT − H]− ion with little fragmentation. The results are discussed in terms of the molecular structure of the isomers.
Four isomers of [C3H8O]+˙ distinguished by collisional activation
Authors: Crow Frank W. , Gross Michael L. , Bursey Maurice M.
Published: May 2005

Collisional activation of the molecular ions of 1‐propanol, 2‐propanol and methyl ethyl ether, and of the m/z 60 ion from 1,2‐dimethoxyethane provides evidence for four distinct forms of [C3H8O]+˙. Collision induced decompositions may be explained either by simple cleavages, by cyclic processes involving adjacent substituents, or by bicyclic processes of adjacent substituents. Evidence for a form of [C3H8O]+˙ in which charge and radical site are separate is assembled from the spectra.
Studies of consecutive reactions of quinones in a reversed geometry mass spectrometer
Authors: Proctor C. J. , Kralj B. , Larka E. A. , Porter C. J. , Maquestiau A. , Beynon J. H.
Published: May 2005

Consecutive reactions involving the ejection of molecules of carbon monoxide from quinone systems have been studied. Using a reversed geometry double focusing mass spectrometer, the individual steps of a consecutive reaction may be separated into different field free regions. The structure of ions formed in the ion source may be compared with those formed from the fragmentation of metastable ions in a field free region by studying differences in the pattern of translational energies released when they break. In the case of anthraquinone it is found that two structures exist for the [MCO]+˙ ion. Critical energy measurements strengthen this argument. Furthermore, 18O labelling has been used to distinguish between the loss of carbon monoxide from different positions on the molecular ion of 1‐hydroxyanthraquinone.
A study of the tautomerism of 5‐as‐triazinones by mass spectrometry
Authors: Daunis Jacques , Djouai‐Hifdi Laila , Pigière Christian
Published: May 2005

The tautomeric equilibria of variously substituted 5‐triazinones have been studied by comparing their mass spectra with those of their methylated derivatives. The results for 6‐methyl‐5‐triazinone have been confirmed by comparison with the mass analysed ion kinetic energy spectra of ions generated from N‐ethyl derivatives. The equilibria are dependent upon the nature of the substituents in the 3‐ and 6‐positions.
Gas phase equilibration of triphenyl cyclohexenyl and diphenyl cyclopentenyl benzyl cations
Authors: Das K. G. , Reddy G. Sudhakar , Wolfschütz R. , Schwarz H.
Published: May 2005

Evidence for the gas phase equilibration of triphenyl cyclohexenyl and diphenyl cyclopentenyl benzyl cations directly or through common intermediates has been obtained from chemical ionization/collisional activation and kinetic energy release data.
Electron impact mass spectra of 2‐(2‐pyridyl)methylene‐1,3‐dicarbonyl compounds: Unusual abundance of the [M + 1]+ ion and the effect of stereochemistry
Authors: Pohjala Esko K. , Nieminen Antti O. K.
Published: May 2005

Electron impact mass spectra of 2‐(2‐pyridyl)methylene‐1,3‐dicarbonyl compounds and related heteroaryl species have been investigated. In 3‐(2‐pyridyl)methylene‐2,4‐pentanedione, its 6′‐methyl and 6′‐methoxycarbonyl derivatives and in E‐ and Z‐ethyl 3‐oxo‐2‐(2‐pyridyl)methylenebutanoates the base peak arises from the loss of methyl radical from the molecular ion to produce a 3‐oxo‐3H‐indolizinium ion. A marked difference is observed in the behaviour of the geometric isomers of the keto esters. The diketones and E‐keto ester carrying a 2‐pyridyl substituent and ketone functionality on the same side of the carbon‐carbon double bond exhibit an unusually high [M + 1]+/[M]+˙ ratio (about 2.5) under normal ionization conditions (pressure 10–100 μPa). This abnormality is a function of pressure only and independent of temperature. In the case of the Z‐keto ester, the corresponding malonate, 3‐ and 4‐(2‐pyridyl)methylene‐2,4‐pentanediones, and 2‐furyl, 2‐thienyl and phenyl diketone analogues, the ratio does not differ much from that due to the natural isotope abundance. Results for 1,1,1,5,5,5‐hexadeuterio‐2‐(2‐pyridyl)‐methylene‐2,4‐pentanedione (strong M + 2 peak) suggest one mass unit transfer as an intermolecular proton shift from a methyl group to give a 3‐hydroxy‐3‐methyl‐3H‐indolizinium ion. This real mass spectrometric phenomenon is a unique example of low pressure self‐chemical ionization.
Photodissociation of gaseous [C5H8]+˙ ions
Authors: Wagner‐Redeker W. , Levsen K.
Published: May 2005

Photodissociation permits the distinction of four isomeric [C5H8]+˙ ions (ionized 2‐pentyne, 1,2‐pentadiene, 1,3‐pentadiene and cyclopentene) which cannot be identified via collisional activation spectrometry. Both the relative cross‐section for photodissociation and the relative abundance of the photodissociated fragments can be used to characterize the ion structure. Furthermore, upper and lower limits for the barrier for interconversion between 1,3‐pentadiene and the other isomers can be determined.
Secondary ion mass spectra of oligopeptides
Authors: Kambara Hideki , Hishida Shinzaburo , Naganawa Hiroshi
Published: May 2005

Secondary ion mass spectrometry for oligopeptides, such as tri‐tetra‐, penta‐ and hexapeptides, and bioactive peptides, are presented. Quasimolecular ions and cationized molecules were observed, together with many kinds of fragments, which were helpful in structural assignments. Secondary ion mass spectrometry did not prove to be dependent on temperature. Thermal migration of samples on a surface was observed at high temperature. Secondary ion mass spectra obtained with a silver substrate and an aluminium substrate are compared.
Energy dependence of the fragmentation of some isomeric [C6H12]+˙ ions
Authors: Herman Jan A. , Li Yip‐Hoi , Harrison Alex. G.
Published: May 2005

The charge exchange mass spectra of 14 C6H12 isomers have been determined using [CS2]+˙, [COS]+˙, [Xe]+˙, [CO]+˙, [N2]+˙ and [Ar]+˙ as the major reactant ions covering the recombination energy range from ∼10.2 eV to ∼15.8 eV. From the charge exchange data breakdown graphs have been constructed expressing the energy dependence of the fragmentation of the isomeric [C6H12]+˙ molecular ions. The electron impact mass spectra are discussed in relation to these breakdown graphs and approximate internal energy distribution functions derived from photoelectron spectra.
A fast atom bombardment study of methionine in combination with deuterium labelling
Authors: van der Greef J. , de Brauw M. C. Ten Noever , Zwinselman J. J. , Nibbering N. M. M.
Published: May 2005

The mechanism of ion formation from methiomine under fast atom bombardment conditions shows similarities with those reported in secondary ion, laser desorption and field desorption mass spectrometry. Deuterium labelling has indicated that the mode of fragmentation of this compound upon fast atom bombardment closely resembles that observed under chemical ionization conditions using methane as reagent gas.
The formation, stability and decomposition of [RXH]+ (XNH2, SH, OH and Cl) ions during hydrogen chemical ionization mass spectrometry
Authors: Colosimo Marcello , Brancaleoni Enzo
Published: May 2005

The relevant peaks of the H2 chemical ionization mass spectra of C1C4 amines, thiols, alcohols and chloroalkanes are reported. The stability of alkylonium ions is discussed on the basis of the proton affinity of the starting neutrals, the substituent alkyl group, and the functional group. The main decomposition paths of [M+1]+ ions are described, and the formation of significant ions is discussed.
Mass spectrometry of nitroazoles: 4—ortho effects: The loss of CHO˙ and CH2O from methyl substituted nitrodiazoles
Authors: Luijten W. C. M. M. , van Thuijl J.
Published: May 2005

The interaction between methyl and nitro groups in some methyl substituted nitropyrazoles and ‐imidazoles causes the expulsion of CHO˙ and CH2O. This may occur when the two substituents are at adjacent positions in the ring. Labelling with deuterium and 13C shows that the loss of CHO˙ and CH2O originates exclusively from the substituents. The isotope effects observed in partially deuterated 3(5)‐methyl‐4‐nitropyrazole are consistent with a hydrogen transfer prior to fragmentation.
Mass spectrometry of 2,5‐dimercapto‐1,3,4‐thiadiazole methyl and aryl derivatives
Authors: Bottino Franscesco , Caccamese Salvatore , Pappalardo Sebastiano
Published: May 2005

The most significant mass spectral features of thirteen title compounds are discussed. Fissions occur across the thiadiazole ring, leading to the formation of [M‐RSCN]+˙ and \documentclass{article}\pagestyle{empty}\begin{document}${\rm R - }\mathop {\rm S}\limits^{\rm + } = {\rm C} = {\rm S}$\end{document} ions. In cases where the thiol‐thione equilibrium is present in the vapour state, expulsion of CS2 from the molecular ion is observed. The fragmentation pattern of the compounds having an ortho nitro group in the S‐aryl moiety is strongly affected by a prominent ‘ortho effect’.
The structure and dissociation pathways of protonated methanol: An ab initio molecular orbital study
Authors: Nobes Ross H. , Radom Leo
Published: May 2005

Ab initio molecular orbital calculations with moderately large polarization basis sets and including valence‐electron correlation have been used to examine the structure and dissociation mechanisms of protonated methanol [CH3OH2]+. Stable isomers and transition structures have been characterized using gradient techniques. Protonated methanol is found to be the only stable isomer in the [CH5O]+ potential surface. There is no evidence for a tightly‐bound complex, [HOCH2]+…︁H2, analogous to the preferred structure [CH3]+…︁H2 of [CH5]+. Protonated methanol is found to possess a pyramidal arrangement of bonds at the oxygen atom with a barrier to inversion of 8kJ mol−1. The lowest energy fragmentation pathways are dissociation into methyl cation and water (predicted to require 284 kJ mol−1 with zero reverse activation energy) and loss of molecular hydrogen (endothermic by 138 kJ mol−1 but with a reverse activation barrier of 149 kJ mol−1). The results offer a possible explanation as to why production of [CH2OH]+ from the reaction of methyl cation with water is not observed. Other dissociation processes examined include loss of a hydrogen atom to yield the methylenoxonium radical cation or methanol radical cation (requiring 441 and 490 kJ mol−1, respectively) and loss of a proton to yield neutral methanol (requiring 784 kJ mol−1).
Diethanolamine assisted secondary ion mass spectrometry of naturally occurring complex oligosaccharides
Authors: Harada Ken‐ichi , Suzuki Makoto , Kambara Hideki
Published: May 2005

A remarkable technique for identifying the molecular weight of involatile and/or thermally unstable compounds by molecular secondary ion mass spectrometry is described. This technique uses diethanolamine as a matrix material instead of glycerol which is at present considered to be the best medium. When this amine is used, adduct ions [M+DEAH]+ are formed from neutral saccharides, and these are very stable for reliable molecular weight determination.
The proton affinity of thioformaldehyde. Implications for the heat of formation of thioformaldehyde and thiolmethyl carbonium ion from ion cyclotron resonance investigations of the proton transfer reactions of [CH2SH]+
Authors: Roy M. , McMahon T. B.
Published: May 2005

Ions at m/z 47 have been generated from a variety of organosulfur compounds both at 70 eV and near threshold. From observations of the energetics of proton transfer from m/z 47 to reference bases of known proton affinity, the species obtained in all cases has been shown to be [CH2SH]+ rather than [CH3S]+. This result is shown to be consistent with recent ab initio calculations on these two isomers and collisional activation experiments.
Mass spectrometry of thio analogues of pyrimidine bases: 4‐alkoxycarbonyl‐alkylthiouracils
Authors: Wyrzykiewicz E. , Buczek J.
Published: May 2005

The mass spectral fragmentation of twelve new 4‐alkoxycarbonylakyithio substituted derivatives of uracils is discussed and fragmentation pathways. Elucidation of which assisted by accurate mass measurements and metastable transitions, are proposed. The comparison between the mass fragmentation of 2‐ and 4‐alkoxycarbonylakylthiouracils have shown that the position of uracil ring thiation may be deduced on the basis of mass special fragmentation patterns.
A mass spectral investigation of water and acetic acid elimination from 1‐ and 2‐indan derivatives
Authors: Groenewold G. S. , Gross M. L. , Zey R.
Published: May 2005

Water and acetic acid eliminations from 1‐ and 2‐indan derivatives have been investigated. Deuterium labeling, high resolution peak matching and the metastable peak analysis capabilities of a high resolution triple analyzer (E B E) mass spectrometer were employed to examine the eliminations. These experiments showed that water was lost from 1‐indanol via 1,2 and 1,3 processes. These results contrast with those obtained for 1‐tetralol, which specifically eliminates water in a 1,4 process involving the benzylic hydrogens. Water elimination from 2‐indanol is preceded by a slow hydroxyl‐benzylic hydrogen exchange and proceeds specifically 1,2. Water losses from both 1‐ and 2‐indanol are characterized by large kinetic energy releases. Acetic acid elimination is shown to occur specifically 1,3 from 1‐acetoxyindan and 1,2 from 2‐acetoxyindan.
Unimolecular reactions of isolated organic ions: Some isomers of [C7H16]+˙
Authors: Wendelboe Jen S. F. , Bowen Richard D.
Published: May 2005

The slow unimolecular reactions of six isomers of [C7H16]+˙ are reported and discussed. These results are interpreted in terms of dissociation via complexes of incipient carbonium ions and the appropriate associated radical. In some cases, rearrangement of the incipient carbonium ion precedes or accompanies decomposition; such isomerization generally favours alkyl radical loss, relative to elimination of the corresponding alkane.
Electron impact mass spectrometry of 2‐hydroxymethyl‐3,4,5,6,7,8‐hexahydro‐2 H‐1‐benzopyran‐5‐ones. The unusual presence of [MH3O]+ species in the fragmentation pattern of 4‐phenyl derivatives
Authors: Bravo Pierfrancesco , Ticozzi Calimero , Traldi Pietro
Published: May 2005

The mass spectrometric behaviour of some 2‐hydroxymethyl‐3,4,5,6,7,8‐hexahydro‐2H‐1‐benzopyran‐5‐ones is described and discussed with the aid of exact mass measurements, linked scans, labelling experiments and low electron energy measurements. The unusual presence of abundant [MH3O]+ species in the mass spectra of 4‐phenyl substituted compounds is discussed in detail and a mechanism is proposed.
The question of tautomerism of alkylnitrile and isonitrile radical cations
Authors: Chess Edward K. , Lapp R. L. , Gross Michael L.
Published: May 2005

The isomeric pairs [CH3CN]+˙ and [CH2CNH]+˙ and [CH3NC]+˙ and [CH2NCH]+˙ have been established as stable, noninterconverting structures. The conclusion derives from studies of collision induced decomposition spectra. The same conclusion pertains for the ions [CH3CH2CN]+˙ and [CH3CHCNH]+˙, and for [NCCH2CH2CN]+˙, [HNCCHCH2CN]+˙ and [HNCCHCHCNH]+˙. The energy barrier of a [1,3]‐hydrogen shift, a possible isomerization mechanism, is determined to be at least 163 kJ mol−1 for the [CH3CN]+˙ and [CH2CNH]+˙ pair, and the barrier may be as high as 318 kJ mol−1. The C3H5N and C4H4N2 radical cations decompose before they can be activated with 318 kJ mol−1 of internal energy.
Doubly charged ion mass spectra: V—Oxygen containing hydrocarbons
Authors: Teleshefsky L. A. , Jones B. E. , Abbey L. E. , Bostwick D. E. , Burgess E. M. , Moran T. F.
Published: May 2005

Doubly charged ion mass spectra were obtained for 46 low molecular weight oxygen containing compounds. A double focusing Hitachi RMU‐7L mass spectrometer, operated at 3.2 kV accelerating voltage, was used to measure spectra for aliphatic alcohol, ketone, ether, aldehyde, ester and acid molecules, as well as several aromatic oxygen containing compounds. In general, the spectra were dominated by fragment ions which resulted from extensive H loss and CC bond rupture as well as O elimination from the doubly charged molecular ions. Total product ion intensities from doubly charged ion spectra of aliphatic oxygen containing compounds were approximately 1% of the corresponding total ion intensity in the benzene doubly charged ion spectrum. Appearance energies for forming prominent doubly charged molecular and fragment ions were determined. Measured values ranged from 26 to 45 eV. A geometry optimized quantum mechanical SCF treatment was used to compute the energies, charge densities and structures for several of these oxygen containing doubly charged ions.
Dimer formation in methane chemical ionization mass spectrometry of organic functionalities, including 2‐azaadamantane derivatives
Authors: Bezoari Massimo D. , Kovacic Peter , Gagneux André R.
Published: May 2005

The methane chemical ionization mass spectra of 1‐hydroxy‐2‐azaadamantane, its lactolactam, and 1‐chloro‐2‐azaadamantanes exhibit high intensity dimeric species. These correspond to [2M+H]+ or stable fragments formed via gas phase chemical reactions, such as dehydration (aminol case) or dehydrohalogenation (chloroazaadamantanes). The tert‐amino chloroazaadamantane forms a stable [2M+C2H5]+ ion with much higher intensity than the [2M+H]+ ion. Similar dimeric species were observed with simple functionalities, including amide, amine, alcohol and alkene. Pressure, temperature and, apparently, steric effects play important roles. Structures are proposed for the various dimeric ions.
Fast atom bombardment mass spectra of involatile sulphonated azo dyestuffs
Authors: Monaghan John J. , Barber Michael , Bordoli Robert S. , Sedgwick R. Donald , Tyler Andrew N.
Published: May 2005

Fast atom bombardment mass spectra of a range of involatile mono and disazo sulphonated dyestuffs are presented. Excellent spectra are obtained for dyestuffs containing up to five sulphonate groups. The fragmentations are discussed with special reference to the ions formed by cleavage of the azo linkage. The negative ion spectra are shown to be superior to those obtained in the positive ion mode.
Gas phase electron attachment reactions and negative ion mass spectra of tris‐ and bis(N,N‐diethyldithiocarbamato) metal complexes
Authors: Gregor I. K. , Guilhaus M.
Published: May 2005

Results are presented for the gas phase thermalized electron attachment reactions of transition metal dithiocarbamates Metal·[S2CN·Et2]n, with n = 3 for the trivalent metals Cr, Mn, Fe, Co and n = 2 for the divalent metals Fe, Co, Ni, Pd and Cu. Details of negative ion mass spectra are given, and these were obtained by use of the complementary methods of in‐beam direct insertion and desorption chemical ionization of samples into temperature and pressure controlled ion source methane gas plasmas. For the tris‐complexes, only small abundances of [M]− were observed, being consistent with the electron entering a metal‐based orbital to give a reduced [MetalII·L3]*− species—the precursor of the observed [MetalII·L2]− or [L]− product ions. For the bis‐complexes, a much higher proportion of the total ion current was carried by [M]−, with [L]− being the next most abundant species in all cases and the principal product in the reaction sequence \documentclass{article}\pagestyle{empty}\begin{document}${[{\rm Metal}^{{\rm II}} \cdot {\rm L}_{\rm 2}] + {\rm e} \to [{\rm Metal}^{\rm I} \cdot {\rm L}_{\rm 2}]^{*-} \mathop {\rightarrow}\limits^* [{\rm L]}^{\rm - } + [{\rm Metal}^{\rm I} \cdot {\rm L}].}$\end{document}. Rearrangement ions [L·MetalI·X]− with X=SH, SCN, NEt2 were also identified for this series which can be accounted for by rearrangement reactions occurring in ligands not fulfilling a bidentate function towards the relevant metal.
Detection of C‐nitroso dimer formation by field desorption mass spectrometry
Authors: Johnson R. L. , Lever O. W. , Brent D. A.
Published: May 2005

Field desorption mass spectrometry is shown to be a useful technique for observing dimer formation in C‐nitroso compounds. Mixed dimer formation (RN2O2R′) is shown to be readily observed by field desorption mass spectrometry.
Electron impact mass spectrometry of 2‐(2‐pyridyl)‐2,3‐dihydroxy‐5‐phenyl‐4‐pentene
Authors: Clerici Angelo , Traldi Pietro
Published: May 2005

The mass spectrometric behaviour of 2‐(2‐pyridyl)‐2,3‐dihydroxy‐5‐phenyl‐4‐pentene has been studied with the aid of B/E, B2/E linked scans, exact mass measurements, collisionally activated dissociation mass‐analysed ion kinetic energy spectra, and labelling experiments. The primary loss of water is proved to involve both hydroxylic hydrogens, thus suggesting the formation of an epoxidic radical ion and the presence of extensive skeletal rearrangements.
Unexpected structural integrity of gas phase isoquinoline cations that eliminate HCN
Authors: Baldwin Michael A. , Gilmore Jeremy , Mruzek Margaret N.
Published: May 2005

13C labelling has been used to study isoquinoline molecular ions undergoing breakdown by HCN elimination in a mass spectrometer. For otherwise stable ions caused to fragment by collisional activation, there is no skeletal rearrangement prior to HCN loss. Of the ions formed by 70 eV electron impact, 69% of those which fragment in the ion source by HCN loss retain their structural integrity, as do 44% of the metastable ions. Of the ions that eliminate HCN without prior arrangement, approximately two‐thirds eliminate C‐1 and one‐third eliminate C‐3. Critical energies are reported for the elimination of HCN from pyridine and isoquinoline molecular ions.
Ionization and dissociation of diethylamine by field ionization mass spectrometry
Authors: Zahran N. F. , Helal A. I.
Published: May 2005

The field ionization mass spectrum of diethylamine on a 5 μm activated wire at 300 K yields surface product ions like protonated molecular ions and doubly charged ions as well as gas phase ions like parent minus CH3 group. Variations of the reaction rate as a function of the decomposition times in the range 10−11‐10−6 s for the elimination of a CH3 group are studied. The reaction rates are evaluated with the help of the retarding potential technique.
The mechanism of the loss of H2 and H2O from 1,4‐cyclohexanediol anion and related compounds
Authors: Gäumann T. , Stahl D. , Tabet J. C.
Published: May 2005

Losses of H2 and H2O from the [M‐H]− alkoxide anions of 1,4‐cyclohexanediol formed in OH− negative chemical ionization were studied using synthetic deuterated analogues and labelling by hydrogen‐deuterium exchange between neutrals in the ion source prior to ionization. Simple 1,2‐H2 elimination leading to an enolate ion does not occur, but stereospecific mechanisms are shown to give a ketolate intermediate daughter ion. Collisionally activated dissociation spectra of the resulting daughter ions are the same as those of the corresponding ions generated directly from ketols.
Metastable ion studies. 4—mass spectral fragmentation and isomerization in the esters of chlorinated propenoic acids
Authors: Korhonen Ilpo O. O.
Published: May 2005

Metastable peaks have been used to study the fragmentation pathways of the methyl and trideuteriomethyl chloropropenoates and chloromethyl propenoate. The molecular ion peaks of the unsaturated esters are more intense than those of the saturated esters, α‐Cleavage, [MOCH3]+, produces the base peak in almost all compounds, the relative abundances of the additional peaks being low for chloromethyl propenoate. The losses of H2O, CH3. and COOH. indicate the isomerization of some ionized chloro esters to the chlorinated 2‐butenoic acid molecular ions. An intense loss of H2O observed for methyl 2‐chloropropenoate indicates its most facile isomerization, [ester]+˙ → [acid]+˙, whereas the isomerization in methyl trichloropropenoate could not be observed. The molecular ion of chloromethyl propenoate, however, also seems to partly rearrange to the chlorinated 3‐butenoic acid ion, since the first field free region metastable peak shows a weak loss of CO. The new reaction pathways, i.e. the losses of CHO˙, CH2O and CH2CO from ionized chloromethyl propenoate, were detected.
Structure determination of some C4H5N+˙Ions from substituted pyridines by collisionally activated dissociation mass spectrometry
Authors: Van Tilborg M. W. E. M. , Van Thuijl J.
Published: May 2005

A standard procedure for recording and correcting collisionally activated dissociation mass spectra is proposed, and used to distinguish between the C4H5N+˙ions formed from hydroxy‐ and amino‐pyridines after loss of CO and HCN, respectively. It is concluded that these ions are cyclic. From the 4‐isomers the 3H‐pyrrole ion is formed whereas from 2‐hydroxypyridine the 1H‐pyrrole ion is formed. In the other cases, mixtures of 2H‐ and either 1H‐ or 3H‐pyrrole ions are generated, depending on the nature of the precursor.
The role of charge‐site location in fragmenting ions. 1—[CH3 CHXCOOCH3]+˙ and [CH2XCH2 COOCH3]+˙ ions and the structures of daughter ions derived from the loss of X (X = I, Br, Cl and CH3)
Authors: Burgers Peter C. , Holmes J. L. , Lossing F. P. , Povel Frank R. , Terlouw Johan K.
Published: May 2005

The structures of the m/z 87, [C4H7O2]+, ions generated by dissociative ionization of CH3CGXCOOCH3 and XCH2CH2COOCH3 (X = CH3, Cl, Br, and I) have been investigated via their unimolecular and collisionally activated fragmentations and by apperance energy measurements. For both precursors loss of X = CH3 produced, via H atom transfer, ions of structure \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm CH_2 = CH}\mathop {\rm C}\limits^{\rm + } \left({{\rm OH}} \right){\rm OCH}_{\rm 3} $\end{document} (a), ΔHf = 386 kj mol−1. In marked contrast, loss of I˙ from ionized CH3CHICOOCH3 and ICH2CH2COOCH3 proceeded without rearrangement to yield respectively ions of structure \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm CH_3}\mathop {\rm C}\limits^{\rm + } {{\rm HCOOCH_3}} $\end{document} (b), ΔHf = 480 kJ mol−1 and (c), ΔHf = 450 kJ mol−1. These different fragmentation behaviours are explained via photoelectron spectra which show that the formal charge site in the precursor ion is at the carbonyl oxygen when X = CH3 but at the halogen atom when X = I. The precursor molecules X = Cl and Br display both of the above characteristics, CH3CHXCOOCH3 yielding mixtures of a and b and XCH2CH2COOCH3 producing a and c ions.
Mass spectra of aurones
Authors: Varma Rajender S. , Bowen Richard D.
Published: May 2005

The mass spectra are reported for 19 aurones (2‐benzylidenecoumaran‐3‐ones) having a wide variety of functional groups and substitution patterns. The principal ions in these spectra are consistent with the operation of proximity effects demonstrated previously for 6‐methoxyaurones.
Charge reversal of the enolate ions of acetaldehyde and acetone
Authors: Lehman Thomas A. , Bursey Maurice M. , Hass J. Ronald
Published: May 2005

Collisionally activated charge reversal of HCOCH2− and CH3COCH2− produces positive ions whose fragments differ from those of other [C2H3O]+ ions formed by fragmentation of positive molecular ions, including the [C2H3O]+ ions from 2,2‐dichlorethanol, considered formerly to have the HCOCH2+ structure. The fragmentations of the charge reversed ions are concordant with the RCOCH2+ structures. Least‐squares correlations of the collisional activation spectra [C2H3O]+ are probed as a useful guide to claiming similarity or dissimilarity of ionic structure.
Extended mass range by multiple charge: Sampling quadruply charged quasimolecular ions of poly(ethylene glycol) 4000
Authors: Chan Kelvin W. S. , Cook Kelsey D.
Published: May 2005

Mass spectrometric sampling of quasimolecular ions with charge as high as 4+ has been achieved by Electrohydrodynamic Ionization Mass Spectrometry (EHMS). Triply and quadruply charged sodium ion adducts of poly(ethylene glycol) 4000 oligomers with mass exceeding 3500 u were sampled from glycerol solution without fragmentation. Although the mass of these ions exceeded the nomical mass range of the spectrometer, they were detected because of multiple charge which lowered their mass‐to‐charge ratio. From the mass spectral intensities of these oligomer ions, the number average molecular weight of the polymer was caculated, and found to be in good agreement with results of an ASTM standard method.
The unorthodox loss of propyl from the molecular ions of methoxycyclohexane
Authors: Molenaar‐Langeveld Tineke A. , Nibbering Nico M. M.
Published: May 2005

It is shown by field ionization kinetics, D and 13C labelling and metastable ion studies that the loss of a propyl radical from the molecular ion of methoxycyclohexane occurs via two routes. At a molecular ion lifetime of <10−10 s propyl is eliminated in the ‘classic’ way, i.e. by successive cleavage of the C(1)C(2) bond, 1,5‐H shift from C(6) to C(2) and cleavage of the C(4)C(5) bond. At 10−10 s the other pathway for propyl loss starts to take place, which is initiated by a hydrogen shift from position 3 or 5 to the methoxy group. This leads in a series of steps to the formation of the 3‐methoxyhexene‐1 ion, which eventually eliminates a propyl radical. In some of the steps specific hydrogen‐deuterium exchange processes have been observed.
Mass spectra of chlorinated aromatics formed in pulp bleaching: I—chlorinated catechols
Authors: Knuutinen Juha , Korhonen Ilpo O. O.
Published: May 2005

A systematic study on the electron impact mass spectra of all nine chlorinated catechols in presented. Metastable ion analysis was used to elucidate the fragmentation pathways. The influence of the position of the chloro substituents can be used to distinguish the structural isomers. In this respect the most characteristic fragment ions are [MCHl]+˙, [MHCOOH]+˙, [MCOCl]+, [MHClCO]+˙, [MCHOCl]+˙ and [MHClHCl]+˙.
Energy transfer in the collision induced decomposition of peptide ions formed by field desorption
Authors: Neumann Gregory M. , Derrick Peter J.
Published: May 2005

In the collision induced decomposition of a number of peptide ions formed by field desorption, it has been found that at the optimum pressure of collision gas the translational energy lost by an incident peptide ion increases as peptide ions of increasing mass are considered. The internal energy taken up by any individual peptide ion appears to be directly proportional to its mass.
Quick screening of major constituents in plant tissue by temperature programmed fractionation mass spectrometry
Authors: Mak C. K. , Tse R. S.
Published: May 2005

Temperature programmed fractionation mass spectrometry can be used to quickly screen for the major constituents in plant and herbal tissues. The method is particularly useful if one is searching for a good plant source of a desired compound. It is also shown that simple extraction followed by mass spectrometry has no advantage over the quick screening method. Limitations and possible improvements of the method are discussed.
The mass spectrometric isomerization of 1‐benzoyl‐2‐(2′‐hydroxy)phenylcyclopropane and 2‐phenyl‐2,3,4,5‐tetrahydro‐2,5‐epoxy[1]‐benzoxepin to a common structure
Authors: Bravo Pierfrancesco , Ticozzi Calimero , Daolio Sergio , Traldi Pietro
Published: May 2005

The mass spectrometric isomerization of 1‐benzoyl‐2‐(2′‐hydroxy)phenylcyclopropane and 2‐phenyl‐2,3,4,5‐tetrahydro‐2,5‐epoxy[1]benzoxepin has been studied in detail with the aid of different ionization methods (electron impact, chemical ionization, field ionization, charge exchange) in conjunction with collisionally activated dissociation experiments.
The effect of configuration of gas phase protonated ethenedicarboxylates on their low energy collision induced dissociation behaviour
Authors: Weisz A. , Mandelbaum A. , Shabanowitz J. , Hunt D. F.
Published: May 2005

Low energy collision induced dissociation (CID) spectra were measured by a triple stage quadrupole mass spectrometer for the [MH]+ ions of diethyl and dimethyl esters of maleic, fumaric, citraconic and mesaconic acids. A very high degree of stereospecificity was observed for the geometrically isomeric diethyl esters. The cis esters give rise to very abundant [MHEtOH]+ and [MHEtOHC2H4]+ ions, while the trans isomers exhibit very abundant [MHC2H4]+ and [MH2 C2H4]+ ions. The highly stereospecific processes indicate that the double bond configuration is retained in the protonated species under the conditions of the experiment.
The fast atom bombardment mass spectra of xanthane dyes
Authors: Brown R. M. , Creaser C. S. , Wright H. J.
Published: May 2005

The Fast Atom Bombardment mass spectra of a number of xanthane dyes are reported. These dyes are insufficiently volatile to give spectra by conventional electron impact ionization. Fragmentation pathways have been determined by metastable linked scan techniques and accurate masses obtained by peak matching. The xanthane dyes may be readily identified from their FAB spectra by the presence of characteristic ions.
Electron impact and chemical ionization mass spectra of nitro‐substituted polyfunctional isomers
Authors: Kulkarni P. S. , Kamath H. V. , Kulkarni Sheshgiri N.
Published: May 2005

The electron impact and methane and ammonia chemical ionization mass spectra of some selected nitro‐substituted isomeric benzalacetophenones, benzyl ketones and aromatic epoxides have been examined. The isomeric pairs show significant differences in the electron impact and chemical ionization spectra. The EI spectra show cleavage α to the carbonyl as the major fragmentation mode. Under CI conditions subtle differences in the fragmentation modes of isomeric pairs are more enhanced, and elimination reactions are more favoured in the o‐nitro‐substituted compounds than in the para isomers.
Mass spectrometric investigation of phenylthiovinyl chlorides
Authors: Paradisi Cristina , Scorrano Gianfranco , Daolio Sergio , Traldi Pietro
Published: May 2005

Three isomeric phenylthiovinyl chlorides (β‐, E and Z, and α‐) have been examined under EI and FI conditions with particular attention paid to the fragmentation leading to [C8H7S]+ ions via loss of Cl˙. Kinetic energy release data, MIKE and CAD MIKE spectra obtained with these precursors, as well as with model compounds, suggest the thioacylium ion PhCH2CS+ as the predominant structure observed for the [C8H7S]+ species in all cases examined. A comparison is made with the solution behaviour of incipient β‐thiovinyl carbenium ions, which are known to rearrange to the S‐bridged thiirenium structure.
The formation of the anilinium ion from the ammonium ion in the ammonia chemical ionization of substituted benzenes
Authors: Stone John Alfred , Splinter Dena Ellen , McLaurin Joanne , Wojtyniak Anastasia C. M.
Published: May 2005

Compounds C6H5X(X  F, Cl, Br, NO2, CN, OCH3) have been studied under chemical ionization conditions with ammonia as reagent gas. A pulsed electron beam and time resolved ion collection has allowed the determination of the reaction leading to the formation of [C6H5NH3]+ (m/z 94). [NH4]+ reacts with C6H5X(X  F, Cl, Br) to yield m/z 94 but C6H5X (X  CN, NO2) forms this ion only by reactions involving either [NH3]+ or [C6H5X]+. C6H5OCH3 does not form m/z 94.
Low energy, low temperature mass spectra 2—low energy, low temperature mass spectra of some small saturated alcohols and ethers
Authors: Bowen Richard D. , Maccoll Allan
Published: May 2005

This paper reports the low energy, low temperature mass spectra of the 27 alcohols and ethers containing up to five carbon atoms. The observed fragmentation pathways are discussed in energetic terms. Except in one instance, pentan‐1‐ol and 3‐methylbutan‐1‐ol, the spectra are diagnostic of the structure of the compounds; even in this case, subtle differences can be used to determine structure. The advantage of the low energy, low temperature mass spectra in identifying low energy fragmentation routes is emphasized.
Mass spectra of ethenol and its deutero analogues
Authors: Tureček František , Hanuš Vladimír
Published: May 2005

Ethenol, 1‐d‐ethenol, O‐d‐ethenol and Z‐2‐d‐ethenol were prepared by pyrolysis of corresponding 5‐norbornenols at 800°C/2 × 10−6 Torr. The most important fragments in the electron impact mass spectrum of ethenol are [C2H3O]+ and CHO+ and CH3˙. The hydrogen atom eliminated from the molecular ion comes mainly from the hydroxyl group (68%) and to a lesser extent from C(1) (25%) and C(2) (7%). The loss of the hydroxyl hydrogen is preceded by rate‐determining migration of the hydrogen atom from C(1) onto C(2) to yield CH3COH+˙ions that decompose to CH3CO+ and H˙. The loss of deuterium from O‐d‐ethenol shows a very small primary isotope effect (kH/kD=1.07), whereas a significant effect is observed for the loss of hydrogen from 1‐d‐ethenol (kH/kD=1.28). The appearance energy of [C2H2DO]+ from 1‐d‐ethenol, AE=11.32 eV, gives a critical energy for the hydrogen loss, E=203 kJ mol−1, which is 90 kJ mol−1 above the thermochemical threshold for CH3CO++H˙. The appearance energy of CDO+ from 1‐d‐ethenol was measured as 12.96±0.07 eV, which sets the barrier to isomerization to CH3CDO+˙ at 1121 kJ mol−1. The ionization energy of ethenol was found to be 9.22±0.03 eV.
Reaction gas chromatography/mass spectrometry. 4—structure elucidation of cyclic sulphides by gas chromatography/mass spectrometry with the use of on‐line hydrodesulphurization
Authors: Mikaya A. I. , Trusova E. A. , Zaikin V. G. , Volinsky N. P. , Karaulova E. N. , Gal'Pern G. D.
Published: May 2005

A method for structure determination of cyclic sulphides within mixtures is described. It involves the use of a vapour phase hydrodesulphurization micro‐reactor (Raney nickel) located between the chromatographic column and the mass spectrometer (hydrogen and deuterium are used as carrier and reagent gases). A comparative examination of the mass spectra of the cyclic sulphides, as well as of the hydrocarbons and their deuterio analogues (deuterium atoms are bonded to carbon atoms which had been attached to sulphur) derived from the sulphides under the catalytic conditions employed, permits unambiguous determination of the size of the heterocycle and the position of the substituents.
Ortho effects in organic molecules on electron impact. 12—Mechanism of the H2O loss from the molecular ion of 2‐(phenylamino)benzoic acid
Authors: Ramana D. V. , Srinivas R.
Published: May 2005

The mass spectrum of 2‐(phenylamino)benzoic acid is characterized by the presence of the base peak at m/z 195, formed by the expulsion of H2O from the molecular ion. A mechanism for the water loss, involving the COOH and NH functions followed by cyclization leading to the molecular ion of acridone, is proposed based on the study of the substituted derivatives and MIKE spectra.
The generation of triplet methoxy cations
Authors: Burgers Peter C. , Holmes John L.
Published: May 2005

The triplet methoxy cation has been generated in the gas phase by the collision induced charge reversal of methoxy anions. Its heat of formation was estimated to be 1034±20 kJ mol−1, in reasonable agreement with ab initio calculations. 3[H3CO]+ and its isomer [H2COH]+ fragment unimolecularly by loss of H2 via a common transition state and some 60% of the reactant's excess energy appears as translational energy of the products. Large isotope effects are involved in the former's fragmentation. The barrier for the isomerization reaction 3[H3CO]+→[H2COH]+ is small, <20 kJ mol−1. The collision induced dissociation 3[H3CO]+→[H3C]++O proceeds via two reaction channels.
Fragmentation of selected C6H10O isomers: Evidence for a common [C5H7O]+ ion generated by methyl loss from cyclohexene oxide and 5,6‐dihydro‐4‐methyl‐2H‐pyran
Authors: Alai Mehrshid , Rye Robin T. B.
Published: May 2005

The loss of CH3˙ from the molecular ions of cyclohexene oxide and 5,6‐dihydro‐4‐methyl‐2H‐pyran has been investigated. On the basis of metastable peak shape analysis, collision‐induced dissociation/mass‐analysed ion kinetic energy spectra and thermochemical data it is concluded that the same [C5H7O]+ ion is formed in both cases.
Heat of formation for the SH radical by photoionization mass spectrometry
Authors: Traeger John C.
Published: May 2005

Photoionization mass spectrometry has been used to measure the appearance energies for [C2H5]+ from ethanethiol, [C3H7]+ from 2‐propanethiol and [C3H5]+ from 2‐methylthiirane. From the known thermochemistry of these cations and their precursor molecules, a 298 K heat of formation of 138.6±0.4 kJ mol−1 for the SH radical has been derived.
Probing molecular structure by the chemical resolution of hydrogen migrations
Authors: Keough T.
Published: May 2005

Methyl chloride chemical ionization mass spectrometry has been used to probe molecular stereochemistry in simple model systems such as cyclic diols and cyclic dicarboxylic acids. The methylation technique, which is based on the chemical resolution of hydrogen migrations, often yields ionic fragments that enable the differentiation of cis and trans isomers. This technique, like protonation methods, fails to differentiate the isomers of 1,2‐cyclohexanediol. However, it does allow differentiation of the isomers of 1,2‐cyclohexanedicarboxylic acid, species that cannot be distinguished via protonation techniques. The utility of methylation in conjunction with MS/MS is also discussed.
Structure determination of [C3H3N2]+ ions, formed from monosubstituted pyrazoles C3H3N2R, by collision‐induced dissociation mass spectrometry
Authors: Van Tilborg M. W. E. M. , Van Thuijl J.
Published: May 2005

[C3H3N2]+ ions have been generated under electron impact conditions from some monosubstituted pyrazoles C3H3N2R. Collision‐induced dissociation (CID) mass spectra of deuterium‐labelled precursors suggest that the majority of the [C3H3N2]+ ions formed from 1‐nitro‐ and 4‐bromo‐pyrazole retain their cyclic structure, whereas the ions from 3(5)‐bromopyrazole are mainly linear. This is confirmed by the relative values observed for the overall cross‐sections for CID and for ion loss. An isotope effect of the order of 1.5–1.9 has been found for the collision‐induced loss of H˙ from [C3H3N2]+, generated from 3(5)‐ and 4‐bromopyrazole.
Stereoisomeric fragment ions arising from decomposition of enol cation radicals of different internal energy content
Authors: Weiske Thomas , Halim Herman , Schwarz Helmut
Published: May 2005

The least‐squares analysis of collisional activation mass spectra provides evidence that 1,1‐dihydroxy‐3‐methylbutene cation radical (a) and 1‐hydroxy‐1‐methoxy‐3‐methylbutene cation radical (c) (generated in a McLafferty‐type rearrangement from 2‐isopropyl‐3‐methylbutanoic acid and its methyl ester) give rise to product ions b and d, the stereochemistry of which at the double bond is determined by the lifetime (internal energy) of a and c, respectively. Decompositions of a and c in the ion source yield predominantly the less stable cis‐configurated stereoisomers of b and d, whereas dissociation of a and c at longer lifetimes (lower internal energy) results in the formation of the thermochemically more stable trans isomers of b and d. A qualitative MNDO analysis is provided which takes into account the special features of stereoelectronic control of radical chemistry in the cleavage of a carboncarbon bond.
Basicity of azoles. 5—Experimental gas phase basicities determined by mass spectrometry towards ab initio calculated protonation energies
Authors: Flammang R. , Maquestiau A. , Catalán J. , Pérez P. , Elguero J.
Published: May 2005

Using Cooks' method, the relative gas phase proton affinities of six azoles (imidazole, benzimidazole, pyrazole, indazole, 1‐methylindazole and 2‐methylindazole) have been determined. Ab initio calculations have been carried out for these six molecules and the corresponding cations, thus allowing the determination of protonation energies. Even the correlation between these quantities (‐log K = 0.438+0.0744δΔEp) is far from perfect (r2 = 0.863), the order of basicity is the same. Aqueous basicities, pKa values, are totally uncorrelated.
Unimolecular reactions of ionized methyl acetate and its hydrogen‐rearranged isomers
Authors: Wesdemiotis Chrysostomos , Csencsits Roseann , McLafferty Fred W.
Published: May 2005

The proposed formation of [CH3C(OH)OCH2]+˙ (b) as the intermediate in the isomerization [CH2C(OH)OCH3]+˙ (c)⇄b⇄[CH3COOCH3]+˙ (c has been confirmed by preparation of b from CH3COOCH2OCH3. For the three isomers a–c the dominant metastable ion (MI) dissociation, CH3O˙ loss, involves identical kinetic energy release values. The kinetic barriers for a⇄b and b⇄c must be nearly as high as that for CH3O˙ loss from c, as shown by the insensitivity of the mass spectra from collisionally activated dissociation (CAD) of a–c to ionizing electron energy. The H/D scrambling of metastable [CH2C(OD)OCH3]+˙ and c–D3 ions confirm this, indicating that the barrier for a⇄b is slightly below that for b⇄c. Minor low‐energy dissociations include losses of CH4 and CH3OH from a and losses of ˙CHO and CH2O from b. Comparison of MI and CAD spectra of a–c with those from [CH3(OH)CH2O]+˙ (d) and [CH3COCH2OH]+˙ (e) give no evidence for skeletal rearrangement of a–c to d or e.
The behaviour of some ferrocene derivatives under electron impact
Authors: Rapić Valdimir , Filipović‐Marinić Nevenka
Published: May 2005

The behaviour of some mono‐ and di‐substituted ferrocene compounds under electron impact has been investigated by means of low‐resolution mass spectrometry. Some characteristic rearrangement processes have been observed and discussed.
Positive ion–molecule reactions in OCS/hydrocarbon mixtures
Authors: Weil David A. , Platzner I. , Miller Larry L. , Dixon David A.
Published: May 2005

The positive ion–molecule reactions of OCS have been investigated in an ion cyclotron resonance spectrometer. A variety of reactions in OCS/hydrocarbon mixtures have been investigated for various C1C4 hydrocarbons—alkanes, alkenes and alkynes. The formation of organosulfur ions is found in reactions in OCS/hydrocarbon (Cn) mixtures with n <4. Formation of organosulfur ions is observed from hydrocarbon ions reacting with OCS and [OCS]+˙ and S+˙ reacting with the hydrocarbons. The proton affinity of OCS has been determined to be 688.7±8 kJ mol−1 while that of CS2 is measured to be 712.1±8 kJ mol−1. Comparison with the proton affinity of CO2 shows that the proton affinity increases as sulfur is substituted for oxygen.
The use of signal averaging techniques for the quantitation and mass measurement of high molecular weight compounds using fast atom bombardment mass spectrometry
Authors: Grotjahn L. , Taylor L. C. E.
Published: May 2005

The measurement and recording of peak signals at high mass is often difficult and susceptible to a large degree of error. Signal averaging of repetitive scans has been used to improve detection limits and aid nominal mass assignment by peak matching. This is illustrated using glucagon as the reference material to determine the mass of the [MH]+ peak in the molecular ion cluster of Vasoactive Intestinal Peptide, and caesium iodide as reference to mass‐measure a 13‐unit oligonucleotide.
A further structural variation of product yield in collisional activation. Study of CH3S+ from dimethyl disulfide with high precursor ion resolution
Authors: Bursey Maurice M. , Hass J. Ronald
Published: May 2005

The isobaric ions CH332S+ and CH34S+ from dimethyl disulfide were separated and collisionally activated in a four‐sector mass spectrometer. The contributions of minor components to the collisional activation spectrum of the unresolved beam are not correctly predicted from consideration of isotope peak corrections using relative intensities of adjacent peaks in the mass spectrum of CH3SSCH3, because the isobaric components not only have different cross‐sections for fragmentation but also different cross‐sections for transmission of the unfragmented beam through the collision gas. Helium collision spectra of the two components are given.