bluuebunny/crossref_metadata_2025 huggingface dataset:
On the nature of the ‘methoxy’ cation
Authors: Bouma Willem J. , Nobes Ross H. , Radom Leo
Published: May 2005

Ab initio molecular orbital calculations with large, polarization basis sets and incorporating valence‐electron correlation have been used to investigate the structure of the [COH3]+ ion formed at threshold from fragmentation of dimethyl ether in the mass spectrometer. The results indicate that this ion is the hydroxymethyl cation, [CH2OH]+, formed with excess energy in a two‐step rearrangement‐dissociation process involving an initial 1,2‐hydrogen shift in the dimethyl ether radical cation to yield an oxonium ion intermediate, [CH2OHCH3]+˙, followed by CO bond cleavage. The intermediate oxonium ion is predicted to lie slightly lower in energy than the dimethyl ether radical cation and represents a stable, previously unreported [C2H6O]+˙ isomer. It is suggested that at high energies, decomposition of the dimethyl ether radical cation involves dissociation followed by rearrangement.
The mass spectra of some tris(trimethylsilyl)acylsilanes and tris(trimethylsilyl)silanes
Authors: Brook Adrian G. , Harrison Alex. G. , Kallury R. Krishna M. R.
Published: May 2005

While tris(trimethylsilyl) alkanoylsilanes fragment in the acylsilane form yielding [(Me3Si)3SiCO]+ by α‐cleavage, the molecular ions of their aryl counterparts rearrange to ionized silaethenes prior to cleavage, paralleling known photochemical behaviour. Sila‐allyl type structures are attributed to the stable [MMe˙]+ ions obtained by subsequent cleavage. Metastable ion characteristics reveal the identity of the structures of the monomeric silaethene ions obtained from one of the aroylsilanes and a 1,2‐disilacyclobutane. The non‐compliance of the alkanoylsilanes with their photochemical behaviour is attributed to a preferred elimination of the stable alkyl radical (R˙) from the molecular ions. Several polysilanes display abundant odd‐electron ions which may possess a disilene structure.
The vinyloxonium cation, \documentclass{article}\pagestyle{empty}\begin{document}${\rm CH}_{\rm 2} = {\rm CH - }\mathop {\rm O}\limits^{\rm + } {\rm H}_{\rm 2}$\end{document}, a stable [C2H5O]+ species in the gas phase
Authors: Burgers Peter C. , Terlouw Johan K. , Holmes John L.
Published: May 2005

The charge stripping mass spectra of [C2H5O]+ ions permit the clear identification of four distinct species: \documentclass{article}\pagestyle{empty}\begin{document}${\rm CH}_{\rm 3} - {\rm O - }\mathop {\rm C}\limits^{\rm + } {\rm H}_{\rm 2}$\end{document}, \documentclass{article}\pagestyle{empty}\begin{document}${\rm CH}_{\rm 3} - \mathop {\rm C}\limits^{\rm + } {\rm H - OH}$\end{document}, and \documentclass{article}\pagestyle{empty}\begin{document}${\rm CH}_{\rm 2} = {\rm CH - }\mathop {\rm O}\limits^{\rm + } {\rm H}_{\rm 2}$\end{document}. The latter, the vinyloxonium ion, has not been identified before. It is generated from ionized n‐butanol and 1,3‐propanediol. Its heat of formation is estimated to be 623±12 kJ mol−1. The charge stripping method is more sensitive to these ion structures than conventional collisional activation, which focuses attention on singly charged fragment ions.
Rearrangements and fragmentations of phenyl styryl sulfides: 2—labelling studies
Authors: Dijkstra P. J. , Weringa W. D.
Published: May 2005

Metastable molecular ions of phenyl styryl sulfides may decompose by loss of CH3˙, SH˙, CHS˙, C6H5˙, C6H6 or C7H7˙. Labelling with carbon‐13 and deuterium gave information about the mechanisms of these reactions. It appears that extensive rearrangements occur prior to most of these fragmentations. In the case of phenyl β‐styryl sulfide both phenyl groups and both vinyl carbon atoms are found in the C7H7 fragment in comparable amounts. For phenyl α‐styryl sulfide this fragmentation leads more specifically to the loss of the S‐phenyl group and the β‐vinyl carbon atom. It was concluded that rearrangements occur, partly via symmetric diphenyl ethene sulfide structures, to benzyl phenyl thione ions, from which the fragmentation occurs. For the loss of CHS˙ an earlier proposed mechanism was confirmed. From both compounds the S‐phenyl ring can be lost as C6H5˙ or C6H6 as well as the C‐phenyl ring. Fragmentation occurs from one of the initial structures as well as from benzyl phenyl thione. Loss of CH3˙ is thought to occur after ring closure with formation of dihydrobenzo[b]thiophenes followed by ring opening by rupture of a CS bond. While phenyl β‐styryl sulfide shows a strong tendency towards isomerization to a symmetric structure like 1,2‐diphenylethene sulfide, phenyl α‐styryl sulfide easily rearranges in an electrocyclic reaction with formation of benzyl phenyl thione.
Electron impact mass spectra of chlorinated methyl propanoates
Authors: Korhonen Ilpo O. O.
Published: May 2005

The mass spectral fragmentations of all eleven chlorinated methyl propanoates have been studied. Deuterium labelling and metastable ion analysis were used to elucidate the fragmentation mechanism. The molecular ion peaks of all compounds are small, except methyl 3,3‐dichloropanoate (38%). In most cases α‐cleavage gives the base peak [COOCH3]+, and the loss of a chlorine atom from the molecular ion is characteristic of the 3‐chloro, 3,3‐dichloro and 3,3,3‐trichloro compounds. Metastable ions showed the losses of small neutral molecules such as CH3OH, CH2CO, CO2 and CO from the [MCl]+ ion. α‐Cleavage and the loss of Cl˙ gives an intense [MCOOCH3Cl]+˙ peak, which is the base peak in the spectra of the 2,3‐dichloro and 2,3,3‐trichloro compounds.
Ortho, Effects in organic molecules on electron impact: X—unusual ortho effects of the methyl group in o‐picolinotoluidide
Authors: Ramana D. V. , Sundaram N.
Published: May 2005

The mass spectrum of o‐picolinotoluidide gives rise to three major fragments at m/z 184, m/z 169 and m/z 168, corresponding to the loss of CO from the molecular ion followed by the loss of ṄH2 and ĊH3 by independent pathways. It has been shown that the ortho methyl group and the nitrogen of the pyridine ring in the 2‐position are involved in the formation of these three major fragments observed in the mass spectrum of o‐picolinotoluidide. The mass spectrum of 2‐(o‐toluidino) pyridine, the molecular ion of which can resemble the [MCO]+ ion in o‐picolinotoluidide, also shows loss of CH3 and NH2 radicals from the molecular ions. Based on these observations coupled with the high resolution data, the mass analysed ion kinetic energy spectrometry and high voltage scans of these fragments in both the compounds, two mechanistic pathways have been proposed for the formation of these ions in o‐picolinotoluidide.
Negative chemical ionization spectra of aromatic acids and esters or are negative chemical ionization spectra of use only if one knows what one is looking for?
Authors: Stöckl D. , Budzikiewicz H.
Published: May 2005

It is shown that the appearance of negative chemical ionization spectra where the reactant gas is allegedly used only to produce low energy electrons is dependent upon instrumental parameters as well as the type of reactant gas used. Reactions with neutral or positive plasma particles, ion/molecule reactions of the substrate, and side reactions with ubiquitous trace impurities (O2, H2O) resulting in ions with masses above that of the molecular ion, as well as differing energy distributions of the thermal electrons which are of importance for the fragmentation behaviour can drastically influence the appearance of a mass spectrum.
Combined liquid chromatography time‐of‐flight mass spectrometry: An application of 252Cf fission fragment induced desorption mass spectrometry
Authors: Jungclas Hartmut , Danigel Harald , Schmidt Lothar , Dellbrügge Jörg
Published: May 2005

A 252Cf fission fragment induced desorption mass spectrometer has been coupled on‐line to a high‐performance liquid chromatograph. The polar effluent (MeOHH2O) is introduced directly into a rough vacuum stage, where a thin sample of non‐volatile compounds is collected in a vacuum‐drying process (<1 cm3 min−1). The interface which spans the difference in operating pressure between the collection site and the ion source consists basically of a sample changing disk. Twelve discrete samples are collected consecutively and analysed, typically one per minute. The system has been tested for the quantitative analysis of some antitumor drugs in serum using homologous compounds as internal standards.
Cluster ion structures formed by positive and negative chemical ionization of lactic and other hydroxyacids
Authors: Li Zhong‐min , Kruger T. L. , Cooks R. G.
Published: May 2005

Both positive ion and negative ion chemical ionization mass spectra of hydroxycarboxylic acids (hydroxyethanoic acid, 3‐hydroxypropanic acid, 2‐hydroxypropanoic acid and 1‐phenyl‐1‐hydroxyethanoic acid) show intense oligomeric ions when the samples are evaporated into a chemical ionization source. The observation of oligomeric anionic and cationic species is unusual, and the parallel behavior observed between the positive and negative ion mass spectra is striking. These results are explicable in terms of evaporation of oligomers and their dehydration products from the hot probe, although gas phase clustering reactions of singly charged ions are not excluded. Hydrogen bonding and dehydration provide bonding within each cluster. The structures of the ions have been confirmed by recording the collision induced dissociations of individual cluster ions via their mass analyzed ion kinetic energy spectra. Temperature dependence of the chemical ionization mass spectra provides a method for distinguishing hydrogen bonding from covalent bonding and gives further structural information on the cluster ions.
The mass spectrometry of 4‐arylquinolizid‐2‐ones
Authors: Gołȩbiewski W. Marek
Published: May 2005

The fragmentation pathways of ten 4‐substituted quinolizid‐2‐ones were established using exact mass measurement, deuterium labelling and detection of metastable transitions. The base peak for most ketones was formed by cleavage of the C‐2C‐3 bond (α to the carbonyl group) and the benzylic C‐4N bond. The decompositions examined were compared with those of the Nuphar alkaloids.
Comparison of collisional activation spectra of some positive ions produced both by charge reversal of negative ions and by decomposition of positive ions
Authors: Lehman Thomas A. , Bursey Maurice M. , Harvan Donald J. , Hass J. Ronald , Liotta Dennis , Waykole Liladhar
Published: May 2005

The charge reversal collision induced decomposition mass analyzed ion kinetic energy spectrum of allyl anion has been compared with the collision induced dissociation mass analyzed ion kinetic energy spectrum of allyl cation and found to be identical except for the presence of +2 ions formed by charge stripping in the spectrum of the [C3H5]+ ion. Likewise, the collision induced dissociation mass analyzed ion kinetic energy charge reversal spectrum of [CH3Se]− has been compared with the collision induced dissociation mass analyzed ion kinetic energy spectrum of [CH3Se]+ and found to be identical. A study of the pressure dependence of the collision induced dissociation mass analyzed ion kinetic energy spectrum of [C3H5]+ and [C3H5]− showed increasing fragmentation with increasing collision gas pressure, and suggests that a greater mean number of collisions converts more energy to internal modes in the collision induced dissociation mass analyzed ion kinetic energy experiment even at low pressures.
Analysis of peptides by means of a single focusing mass spectrometer equipped with a molecular beam solid analysis/fast atom bombardment source
Authors: Aubagnac Jean‐Louis , Devienne F. M. , Combarieu R.
Published: May 2005

The use of a molecular beam solid analysis/fast atom bombardment source in conjunction with a single focusing mass spectrometer of limited specification is described for the identification of peptides. This ionization method is shown to have significant advantages for such analyses and the performance of the mass spectrometer is shown to be adequate for this work.
Mass spectrometry of dinucleotide analogues containing 6‐azauracil moiety
Authors: Zasada‐Parzyńska Alicja , Golankiewicz Krzysztof
Published: May 2005

The mass fragmentation of three dinucleotide analogues in which D‐ribose phosphodiester linkages were replaced by a three methylene unit chain has been investigated. The fragmentation pathways were proposed on the basis of high resolution data and metastable transitions. These compounds demonstrated a unique fragmentation with the formation of the fragment ion containing nitrogen at the end of the C3H6 chain.
Negative ion chemical ionization mass spectra of (η6‐arene)Cr(CO)3
Authors: Vaglio Gian Angelo , Volpe Paolo , Operti Lorenza
Published: May 2005

The negative ion chemical ionization mass spectra, with ammonia and methane as reagent gases, of the (η6‐arene)Cr(CO)3 complexes, where the arene is C6H5COCH3, C6H5COC2H5, C6H5COC3H7, C6H5COC(CH3)3, 2‐CH3C6H4COC3H7, C6H5COOCH3, C6H5CH3, 1,3,5‐(CH3)3C6H3 and C6H5CH2COC2H5, are reported. Similar behaviour is observed with the two reagent gases, but ammonia shows a much higher abundance for the ions produced by reactions of [NH2]− with sample molecules. The compounds containing the C6H5CO group display an abundant [M]− ˙, whereas the other compounds exhibit [MH]− as base peak, produced by ion/molecule reactions. A comparison of the negative ion chemical ionization mass spectra of the (η6‐arene)Cr(CO)3 complexes with those of the corresponding ligands shows the strong electron withdrawing power of the Cr(CO)3 group in the gas phase.
Electron impact mass spectra of bifunctional steroids. The interaction between ionic and neutral fragments derived from the same parent ion
Authors: Longevialle Pierre , Botter René
Published: May 2005

Apparent ‘long distance’ H transfers in the fragmentation of bifunctional steroids under electron impact result from an ‘intramolecular’ reaction between ionic and neutral fragments. These transfers are made possible by the independent rotation of the fragments and result from a compromise between their cross‐section and the velocity of separation of the fragments. They are compared with other processes previously described as involving the formation of a ‘complex’ between ionic and neutral fragments derived from the same parent ion.
Gas phase substitution under ammonia chemical ionization
Authors: Das K. G. , Swamy R. A. , van Thuijl J. , Onkenhout W. , Fraisse D. , Tabet J. C.
Published: May 2005

Evidence for the isomerization of the [M + NH4]+ adducts of nitrobenzene and triphenylnitrocyclohexenes to the isonitroso derivatives in the first field free region has been obtained. The isomerized adducts undergo successive loss of ṄO and ȮH or NH3 to give ions corresponding to the substitution products. Mass analysed ion kinetic energy and collisionally activated dissociation/mass analysed ion kinetic energy data reveal that the adduct decomposes by similar pathways in the second field free region. In the ion source an addition elimination reaction and nucleophilic substitution contribute to the formation of the substituted product ion.
The nominal butyl ester ion in the mass spectra of long‐chain n‐alkyl esters: A postscript
Authors: Meyerson Seymour , Kuhn Eugene S. , Puskas Imre , Fields Ellis K. , Leitch Leonard C. , Sullivan Thomas A.
Published: May 2005

n‐Octadecyl benzoate, taken as a model for long‐chain n‐alkyl carboxylates generally, loses C14H28 under electron impact to yield a product with the same elemental composition as the butyl benzoate molecular ion. This product retains quantitatively one hydrogen from C‐6, and seems to be formed as an oxygen‐protonated 4‐benzoyloxybutyl radical. It reacts further to lose H2O, in which deuterium labeling demostrates that the second hydrogen atom comes predominantly from C‐4. The intermediate reorganization, for which the driving force is presumably furnished by the instability associated with a primary radical, is pictured in terms of cyclization via bonding between the C‐4 radical site and the benzoyl carbon concerted with hydrogen migration via a 4‐membered quasicyclic transition state.
Cyclic organophosphorus compounds. XVIII—the mass spectroscopy of some 2‐amino‐1,3,2‐dioxaphosphorinans, cyclic phosphorodiamidates and phosphorodiamidothionates
Authors: Edmundson R. S.
Published: May 2005

Stepwise replacement of O in 1,3‐dioxa‐2‐phospha(V)‐cyclohexanes (or related ring systems) by NR (R=H or Me) leads to an increase in the stability of the hetero‐ring ions produced under electron impact conditions. In the case of the 2‐phenoxy derivatives, there is also an increased abundance of [MPhO]+ or [MPhOH]+ ions, and, for the 2‐sulphides, a reduction in the abundance of [M‐S]+˙ and [M‐SH]+ ions, with a concurrent increase in that of [M‐PhS]+ ions. Such trends have been correlated with ultraviolet photoelectron spectral data on a qualitative basis.
Electron impact mass spectrometry of the acetates of zinc, magnesium, cobalt and manganese
Authors: Marshall G. L.
Published: May 2005

The electron impact mass spectra of the acetates of zinc, magnesium, cobalt and manganese have been investigated using a direct inlet probe. Volatile tetrahedral complexes are produced on heating, and ions of the form [M4(OCOCH3)6O]+˙ (M = Co and Mn) and [N4(OCOCH3)5O]+ (N = Zn or Mg) are observed. A mixture of magnesium and cobalt acetates produces ions of the form [MgnCo4–n(OCOCH3)6O]+˙.
Ion chemistry of phthalamic acids. 2—mass spectral retrosynthesis of phthalanilic acids and structure analysis of [C8H6NO2]+ ions from N‐cyclohexylphthalamic acid and [MH]+ of N‐cyclohexylphthalimide
Authors: Selva Antonio , Traldi Pietro , Ventura Paolo , Servadio Vittorino
Published: May 2005

Under electron impact o‐phthalanilic acids show the retrosynthetic reaction previously described for other phthalamic acids. As primary amine derivatives they undergo thermal and electron impact induced water loss. Like the molecular ions of the related phthalimides, their [MH2O]+˙ do not give [C8H6NO2]+ fragments, which are obtained from the N‐cyclohexyl derivative. The structure of such fragments is investigated by collisionally activated mass analysed ion kinetic energy spectra, and compared with the [MH]+ of phthalimide, obtained by chemical ionization with CH4 or NH3 and assumed to be possible models.
Doubly charged ion mass spectra. 7—acetylenes
Authors: Appling J. R. , Jones B. E. , Abbey L. E. , Bostwick D. E. , Moran T. F.
Published: May 2005

Doubly charged ion mass spectra of 20 aliphatic and 3 aromatic acetylenic compounds have been measured using a double focusing Hitachi RMU‐7L mass spectrometer. Spectra were obtained using 100 eV ionizing electron energy and 3.2 kV ion accelerating voltage. In general, the spectra of aliphatic type acetylenic compounds were dominated by fragment ions formed by extensive H loss from doubly charged molecular ions. Intense molecular ions were observed in the doubly charged ion spectra of phenyl‐substituted acetylenes. Total product ion intensities for doubly charged ion spectra of acetylenic compounds were found to be smaller, in general, than the total product ion intensity observed in the benzene doubly charged ion mass spectrum. Measured appearance energies of intense product ions ranged from 24 to 47 eV. A geometry optimized quantum mechanical self‐consistent field molecular orbital treatment was employed to compute energies and structural parameters of prominent ions in the doubly charged ion mass spectra of acetylenic compounds.
The role of the field in field desorption fragmentation of polyethylene glycol
Authors: McCrae Christine E. , Derrick Peter J.
Published: May 2005

The degree of fragmentation induced during field desorption of polyethylene glycol increases as the potential between emitter and cathode is raised. This fragmentation is explained as field dissociation. The shape of the envelope of pseudomolecular ion peaks depends upon temperature but not upon field. It is suggested that the desorption of pseudomolecular ions proceeds over barriers whose heights are dependent upon the electric field strength.
Electron impact induced water elimination from hydroxyamides. 2—N‐acetyl‐ and N‐benzoyl‐4a‐hydroxydecahydroquinoline and N‐Methyl‐4a‐hydroxy‐2‐oxodecahydroquinoline
Authors: Steiner B. , Schumann D. , Naumann A.
Published: May 2005

Electron impact induced water elimination from the metastable molecular ions of N‐acetyl‐ and N‐benzoyl‐4a‐hydroxydecahydroquinoline mainly follows a formal [1,2] elimination. The initiating and ratedetermining step in the reaction is the hydrogen rearrangement from C‐8a onto the carbonyl group. The transferred hydrogen is subsequently lost, together with the hydroxyl group. The almost complete absence of H2O loss from both diastereomers of N‐methyl‐4a‐hydroxy‐2‐oxodecahydroquinoline confirms that the reaction can only proceed when the carbonyl group is able to function as ‘hydrogen carrier’ by occupying positions in the vicinity of both a hydrogen and the hydroxyl function.
Collisionally activated dissociation spectra of protonated methyl N‐alkanoates studied using a triple quadrupole
Authors: Sun Wing‐Fung , Dawson P. H.
Published: May 2005

The collisionally activated dissociation (CAD) spectra of protonated methyl n‐alkanoates CH3 (CH2)nCOOCH3 with n = 1−9 were studied using a triple quadrupole. The influence of hydrocarbon chain length and collision energy on characteristic fragment ions such as those due to the loss of methanol was examined. It was found that most characteristic fragment ions became less important in the CAD spectra with increasing chain length of the esters and finally disappeared in the higher members of the series. Special care would have to be taken when trying to use such neutral losses in analysis for identifying the presence of a certain class of compounds.
Ortho effects in organic molecules on electron impact: XI—the interesting ortho effect of the methoxy group in o‐methoxy aromatic thioamides
Authors: Ramana D. V. , Viswanadham S. K.
Published: May 2005

It has been noticed that the major part of the loss of ṠH from the molecular ion of most of the o‐methoxythioamides results from an ortho effect of the methoxy group. Comparison of the MIKE spectra of the [MSH]+ of 1‐(2‐methoxyphenylthioxomethyl)piperidine and 1‐(2‐methoxyphenylthioxomethyl)pyrrolidine with the MIKE spectra of [MSH]+ of the corresponding unsubstituted compounds, reported earlier, indicated two parallel pathways for the formation of [MSH]+ in the o‐methoxy compounds. In the first pathway, as has been noticed in thioamides in general, the loss of ṠH involves the migration of either the α‐hydrogen in the amine moiety or the hydrogen attached to nitrogen. In the second pathway, the migration of a hydrogen from the o‐methoxy group to the sulphur atom followed by ejection of SH from the molecular ion leads to a stable cyclized ion. Interesting secondary fragmentations as a consequence of this ortho effect have also been noticed.
Mechanism for semiquinone formation in the oxygen negative chemical ionization mass spectrometry of 2,3,7,8‐tetrachlorodibenzo‐p‐dioxin
Authors: Mitchum Ronald K. , Korfmacher Walter A. , Althaus James R.
Published: May 2005

The high toxicity of 2,3,7,8‐tetrachlorodibenzo‐p‐dioxin (2,3,7,8‐TCDD) has led to the development of selective and highly sensitive quantitative methods for mass spectral analysis. Analytical selectivity has been demonstrated for the oxygen negative chemical ionization (ONCI) reaction of TCDD in an oxygen‐rich plasma. While the reaction product (4,5‐dichloro‐1,2‐benzoquinone anion) of 2,3,7,8‐TCDD and oxygen is well known, the mechanism of its formation has not been studied thoroughly. In this report the results of a study involving the reaction of 18O2 with 2,3,7,8‐TCDD under high pressure and low pressure ONCI conditions are reported. A mechanism is proposed which is compatible with the observation that one 18O atom is incorporated into the product anion.
Mass spectra of some tetrasubstituted 4,4′‐biisoxazoles and 4,4′‐methylendiisoxazoles
Authors: Filipović‐Marinić N. , Sušnik‐Rybarski I.
Published: May 2005

The behaviour of some tetrasubstituted 4,4′‐biisoxazoles and 4,4′‐methylendiisoxazoles under electron impact has been investigated by means of high and low resolution mass spectrometry. The determination of metastable transitions and accurate masses of important fragment ions has led to the construction of fragmentation schemes. Specific skeletal rearrangement processes are discussed and it is proposed that they proceed through azirine and oxazole intermediates.
Mass spectra of halogenated esters 6—Methyl esters of some trihalogenated propanoic and butanoic acids
Authors: Korhonen Ilpo O. O.
Published: May 2005

The mass spectral fragmentation of trihalogenated methyl esters, formed in the reactions of monochlorinated methyl propenoates and 2‐butenoates with Cl2, BrCl and Br2, have been investigated. In most cases α‐cleavage gives the base peak, [COOCH3]+, the peaks originating from the subsequent losses of one or two halogen atoms also being abundant. The primary loss of a halogen atom is more prominent in the C4 derivatives, Br˙ and Cl˙ being preferentially lost from the 2‐ and 3‐positions, respectively. The McLafferty rearrangement yields in one case the base peak; the 2‐halo compounds could in general be distinguished by that fragmentation. Typical for all 2‐bromo‐substituted methyl butanoates studied is the base peak, [C3H3]+, at m/z 39, and for some 3‐halo compounds the peaks at m/z 95, [C2H4ClO2]+ and 139, [C2H4BrO2]+.
Phosphoric amides. 7—Mass spectrometry of phosphoric amido esters: Fragmentation patterns and migratory aptitudes
Authors: Davidowitz Bette , Modro Tomasz A.
Published: May 2005

Mass spectra of 38 organophosphorus compounds, containing both phosphate ester (P(O)OR) and phosphoramidate (P(O)NR′R″) functional groups, were recorded and discussed. Attention was focused on PN bond cleavage, which can involve simple fission, fission accompanied by hydrogen migration from the ester group and fission accompanied by the migration of the ester R group to the departing nitrogen atom. Fragmentations characteristic for the N(β‐chloroethyl) derivatives (phosphorylated nitrogen mustards) are also presented.
The mass spectra of nitrosulphanilamides. Observation of thermally generated products from 4‐(piperidylsulphonyl)‐2‐nitroacetanilide
Authors: Abdel‐Halim A. M. , Bilton J. N. , Waight E. S.
Published: May 2005

In addition to the expected electron impact induced fragmentation, the mass spectra of substituted nitrosulphanilamides, such as 4‐(piperidylsulphonyl)‐2‐nitroacetanilide, exhibit peaks due to imidazoles, imidazole‐N‐oxides and furazans, which are formed thermally in the spectrometer ion source.
A study of the electron impact induced retro‐diels‐alder process with selected 5,6,6a, 7,12,12a‐hexahydrobenzo[a]anthracenes
Authors: Bobenrieth M.‐J. , Levy L. A. , Hass J. R.
Published: May 2005

The mass spectra of 5,6,6a,7,12,12a‐hexahydrobenzo[a]anthracene and 2‐methoxy, 3‐methoxy‐, 4‐methoxy and 1‐methyl‐4‐methoxy derivatives are reported. Among the fragment ions observed under electron impact ionization, [C8H8]+· and [MC8H8]+· can be generated by a retro‐Diels‐Alder process. Studies of metastable ion reactions show these ions to be formed by fragmentation directly from the molecular ion. The CA spectra of the [C8H8]+· ions from the subject compounds were compared with spectra from ions of the same composition from various sources. From these data, kinetic energy release measurements and stereochemical considerations, it is concluded that these ions are formed by a stepwise, rather than a concerted mechanism.
Field ionization and electron impact mass spectra of cycloolefins
Authors: Rang Silvia , Strenze Tiiu , Müürisepp Mati , Eisen Olaf
Published: May 2005

The field ionization mass spectra of monosubstituted cyclopentenes and cyclohexenes with C1‐C7 n‐alkyl and C4‐C5 isoalkyl substituents in positions 1 and 3 have been investigated and compared with the previously reported electron impact mass spectra of these compounds. The cleavage of the CC bond β to the double bond in the non‐isomerized molecular ion was found to be a typical degradation reaction of the higher homologues in the strong electric field. So, by means of the field ionization mass spectra, the >C1 alkyl substituent can be readily located in the parent molecule. The electron impact mass spectra exhibit a less specific fragment ion distribution for positional isomers due to the extensive molecular ion isomerization prior to decomposition, but provide useful information on the ring size. For structure determination it is appropriate to use both ionization techniques.
Collision dissociation study of negative ion chemical ionization (OH−) fragments of bornyl C4C5 esters
Authors: Selva Antonio , Traldi Pietro , Massimo Bambagiotti A.
Published: May 2005

Collisional activation spectra show interesting and specific dissociations which demonstrate the retention of structural identity not only of carboxylate anions discussed in a previous paper, but also of other fragments obtained from bornyl C4C5 esters under negative chemical ionization mass spectral conditions with OH− as reactant ions.
The study of ionic fragmentation by photoelectron‐photoion coincidence spectroscopy
Authors: Dannacher Josef
Published: May 2005

Since its invention, a decade ago, photoelectron‐photoion coincidence spectroscopy has continuously provided extremely important information on ionic fragmentation processes. The outstanding reputation of the technique is essentially founded on the fact that internal energy selected cations can be studied. In striking contrast to the importance of the method and to the reliability of the data obtained, only about 150 coincidence studies have been published up to now. This is due to the rather intricate experimental technique involved and, probably even more, to the main drawback of this method, i.e. the enormous length of time involved in the measurements. The systems investigated so far are comprehensively compiled in the present article. The two experimental variants currently in use, termed fixed and variable wavelength technique, are compared. Evidence for the complementary character of the two experimental versions is presented. It is recalled that the primary source of information is in any case a time‐of‐flight distribution. The different ways of analysing these distributions are summarized and the accuracy of the derived results is discussed. The current state of the art is exemplified by reviewing the outcomes for a number of selected examples. The presented results on di‐, tri‐ and tetra‐atomic cations reveal clearly the more recently achieved experimental progress. Data on such smaller ionic species are particularly useful for studying predissociation mechanisms, a domain which becomes more and more accessible to modern ab initio calculations of fragmentation pathways. The reported results for O2+ and CO2+ reveal that branching ratios for the formation of electronically and vibrationally excited dissociation products can now be quantified for sufficiently small systems. The possibility of distinct behaviour of isoenergetic molecular ions depending on the method of preparation is outlined in the case of formaldehyde cation. The same cation is used to exemplify a puzzling isotope effect originating in a rate‐determining radiationless transition that precedes a significantly faster dissociative step. A variety of data on larger systems grouped according to topic are critically reviewed. The determination and accuracy of rate‐energy functions is discussed, at first for the case of a single decay channel; then the analogous analysis for a series of competing fragmentations is outlined. The importance of competitive radiative and non‐radiative/dissociative depletion of an excited electronic state is pointed out.
The substituent effect on the single and double hydrogen atom transfer reactions in para‐substituted benzoic acid isobutyl esters
Authors: Tobita Seiji , Tajima Susumu , Tsuchiya Toshikazu
Published: May 2005

The substituent effect on the single and double hydrogen atom transfer reactions in para‐substituted benzoic acid isobutyl esters has been investigated by electron impact mass spectrometry. Electron‐donating substituents favour formation of the [MC4H8]+˙ ion generated by single hydrogen atom transfer reaction (McLafferty rearrangement), whereas electron‐withdrawing substituents favour formation of the [MC4H7]+ ion generated by double hydrogen atom transfer reaction. In the case of the latter compounds, the m/z56 ([C4H8]+˙) ion, which is generated by single hydrogen atom transfer reaction with charge migration, is very intense, while in the former compounds, the m/z56 ion is very weak. These observations can be reasonably explained on thermochemical grounds based on the sum of the standard heats of formation of the fragments.
Isomerization of [C6H5C3H5O]+˙ ions: The case of 1‐phenylpropenol
Authors: Denhez J. P. , Audier H. E.
Published: May 2005

Appearance energy and kinetic energy release measurments together with isotopic labelling have shown that the meastable molecular ion of 1‐phenylpropenol isomerizes into those of cinnamic alcohol and 3‐phenylpropanal prior to loss of ketene. 13C labelling and thermodynamic considerations prove that the rearrangement of 1‐phenylpropenol occurs by an ‘ortho attack’ leading to bicyclic intermediates. Statistical hydrogen exchanges are observed prior to fragmentation. The isomerization mechanisms are discussed.
Differentiation of polycyclic aromatic hydrocarbons using electron capture negative chemical ionization
Authors: Buchanan Michelle V. , Olerich Geraldine
Published: May 2005

A number of isomeric polycyclic aromatic hydrocarbons may be distinguished using electron capture negative chemical ionization when methane is used as a buffer gas, including benzo[a]pyrene and benzo[e]pyrene. The ionization behavior of these compounds may be predicted, on the basis of their electron afinities, allowing compounds to be distinguished without the use of standards.
Mass spectrometry of bis‐quinolizidine alkaloids: Lactams of sparteine and α‐isosparteine
Authors: Majchrzak‐Kuczyńska U. , Wiewiórowski M. , Wyrzykiewicz E.
Published: May 2005

The mass spectral fragmentations of 2‐oxosparteine (lupanine), 2‐oxo‐α‐isosparteine (α‐isolupanine), 15‐oxosparteine, 17‐oxosparteine and 10‐oxosparteine (aphylline) are reinvestigated and discussed. Fragmentation pathways, elucidation of which were assisted by accurate mass measurements and metastable transitions, are proposed. The fragmentation assignments are not consistent with those previously reported in the literature. Many fragment species of the same m/z (low‐resolution spectra) are composed of two or three fragment ions of different elemental compositions (high‐resolution spectra). The obtained data create a safe basis for distinguishing structural and stero isomers.
Structure and fragmentation of dimethyl methylphosphonate and trimethyl phosphite
Authors: Holtzclaw James R. , Wyatt Jeffrey R. , Campana Joseph E.
Published: May 2005

The structures and fragmentation pathways of two isomeric organophosphorus esters, dimethyl methylphosphonate (DMMP) and trimethyl phosphite (TMP) have been determined. The long‐lived, low‐energy molecular ions of DMMP were found to undergo a keto‐to‐enol isomerization prior to collision‐induced dissociation. This isomerization was established through the comparison of the collision spectra from DMMP, TMP, isotopically labeled DMMP and a model precursor ion. Electron ionization and charge exchange reactions were used to study the isomerization as a function of the internal energy of the molecular ion. The structure of the TMP molecular ion retained the structure of the neutral molecule. The daughter ion spectra of the isomeric fragment ions from DMMP and TMP were used to infer the fragment ion structures. Negative ions of DMMP and TMP were also studied, and their collision spectra were found to be indistinguishable.
Mass spectral analysis of Schiff bases derived from 1,1,1‐trifluoro‐2,4‐pentanedione and Bis(3,3′‐aminopropyl)amine and bis(3,3′‐aminopropyl)methylamine and their copper(II) and nickel(II) complexes
Authors: Morris M. L. , Koob R. D.
Published: May 2005

Mass spectra have been obtained for bis(5,5,5‐trifluoro‐4‐oxopentan‐2‐N‐propylene)amine, bis(5,5,5‐trifluoro‐4‐oxopentan‐2‐N‐propylene)methylamine, bis(5,5,5‐trifluoro‐4‐oxopentan‐2‐N‐propylene)aminocopper(II), bis(5,5,5‐trifluoro‐4‐oxopentan‐2‐N‐propylene)aminonickel(II), bis(5,5,5‐trifluoro‐4‐oxopentan‐2‐N‐propylene)methylaminocopper(II) and bis(5,5,5‐trifluoro‐4‐oxopentan‐2‐N‐propylene)methylaminonickel(II) using a Varian‐MAT CH5 mass spectrometer. The first two compounds are seen to fragment primarily in the trimethylene chain γ to the middle nitrogen although fragmentation is seen at a variety of other sites as well. Lower molecular weight ions form a significantly larger fraction of the total ion intensity for the methylated middle nitrogen compound than for its non‐methylated analog. In the metal complexes of these Schiff bases, the metal exerts its influence in two ways. The primary cleavage site inthe trimethylene bridge is β, rather than γ, to the middle nitrogen, and other fragments are produced which are ascribable to ligand to metal electron transfer.
Fast atom bombardment mass spectrometry of alkali metal fluorides and chlorides; a comparison of the solid salt and glycerol matrix spectra
Authors: Miller Jack M. , Theberge Roger
Published: May 2005

The Fast Atom Bombardment (FAB) mass spectra of the alkali metal chlorides (Na, K, Cs) and fluorides (Na, K, Rb, Cs) were obtained from solids and a glycerol matrix, using a fast atom bombardment source. From solids the fluorides exhibited an ion abundance enhancement of the well‐known [M(MF)4]+ cluster, which decreased with increasing cation size. A gradual decrease in the n=4 enhancement was observed as the salt was diluted with glycerol. In the chlorides only sodium chloride showed the n=4 relative enhancement. The mass spectra of the salts from a glycerol matrix at molar ratios of 1:1 to 1:10 showed that the spectra of the 1:1 solutions were similar to those from the solids, while glycerol adducts were found to increase with increasing glycerol concentration. A [M(MX)n(gly)]+ species that featured successive losses of HX was observed. It has not been established whether HX losses take place in solution, in the surface/vacuum interface and/or whether gas phase reactions might be responsible for the observation of the [M(MX)n(gly)–y HX]− species in the mass spectra of the MX/glycerol system.
Fragmentation of trimethylsilyl derivatives of 2‐alkoxyphenols: A further violation of the ‘even‐electron rule’
Authors: Krauss Dietlinde , Mainx Hans Georg , Tauscher Bernhard , Bischof Peter
Published: May 2005

The mass spectra of trimethylsilyl (TMS) ethers of 2‐methoxyphenols show abundant [M–30]+˙ ions originating from consecutive loss of two methyl radicals. This is illustrated by comparison of the accurate mass‐measured and linked‐scan spectra of the TMS derivatives of 2‐methoxyphenol (guaiacol), 4‐hydroxy‐3‐methoxybenzaldehyde (vanillin) and 3‐(4‐hydroxy‐3‐methoxyphenyl)‐2‐propenoic acid methyl ester (ferulic acid methyl ester) with those of the TMS derivatives of phenol, 4‐hydroxybenzaldehyde, 3‐(4‐hydroxyphenyl)‐2‐propenoic acid methyl ester (p‐coumaric acid methyl ester), 3‐methoxyphenol and 4‐methoxyphenol. This distinctive ortho effect is valuable in the identification of isomeric phenolic compounds. In the spectra of the TMS derivatives of 2‐ethoxyphenol and 2‐propoxyphenol the sequential loss of two radicals is less pronounced, because elimination of the side‐chain and a methyl group with rearrangement and hydrogen migration is competitive.
McLafferty reactions in even‐electron ions?
Authors: Zollinger M. , Seibl J.
Published: May 2005

Within the scope of a comparative study of the reactivities of odd‐ versus even‐electron ions, the possible significance of the well‐known McLafferty reaction for structural analysis in even‐electron ions is investigated. In order not to compare reactions of different types with one another, a selective set of experimentally verifiable features is specified which must be met by a degradation reaction to justify its classification as a true McLafferty process. The literature is critically reviewed in the light of this restrictive specification and some ambiguous examples have been reinvestigated, applying modern techniques of selective metastable ion scrutiny together with specific 2H labelling. Only in a few specific cases are even‐electron ions found to decay in a McLafferty fashion according to the postulated criteria, indicating a rather limited effectiveness of the reaction as a source of structural information in this field. Fundamental problems in unequivocally pinning down a very specific mechanistic course of a reaction are encountered in spite of using sensitive new techniques of measurement.
Main fragmentation routes of functionally substituted cyclopropenes under electron impact
Authors: Domnin I. N. , Lakshin A. M. , Misharev A. D. , Takhistov V. V. , König W. A.
Published: May 2005

The behaviour of substituted cyclopropenes under electron impact is to a large extent determined by the presence of the unsaturated three‐membered ring which is capable of efficient delocalization of the positive charge. The loss of one of the substituents at the C(3) position of the small ring is characteristic for the fragmentation of cyclopropenes; the loss of the substituent which is less electron donating occurs preferentially. The presence of substituents with heteroatoms on the three‐membered ring may lead to changes in the fragmentation scheme characteristic for the specific set of substituents.
Mass spectral studies of some rotenoid stereoisomers
Authors: Kostova Ivanka , Mollova Nevena
Published: May 2005

The mass spectral behaviour of several rotenoid stereoisomers is discussed.
A spurious [CH5]− ion: Problems with negative chemical ionization quadrupole instrument
Authors: Poppe A. , Schröder E. , Budzikiewicz H.
Published: May 2005

It is shown that in a quadrupole mass spectrometer set up for negative chemical ionization, positive ions can be formed between the ionization chamber and the analyser both by electron impact and by chemical ionization. These ions will be registered together with negative ions formed in the ion source if the instrument is equipped with a positive and a negative conversion dynode and may reach the secondary electron multiplier even if the negative conversion dynode is disconnected.
Low‐energy, low‐temperature mass spectra. 5‐alkanals
Authors: Maccoll Allan , Mruzek Margaret N.
Published: May 2005

The low‐energy, low‐temperature mass spectra of thirteen alkanals are reported and their predominant modes of fragmentation discussed in terms of energetics. Characteristic of this class of compounds is the very high proportion of odd‐electron ions in the mass spectra, namely [M  CMH2m]+˙, [M  H2O]+˙ and [M  H2O  CmH2m]+˙.
High‐Resolution electron impact mass spectrometry of five novel organoiron complexes
Authors: Lay Jackson O. , Allison Neil T. , Yongskulrote W. , Ferede R.
Published: May 2005

The high resolution mass spectra of five novel η1‐R substituted Fe(II)(CO)2 η5‐C5H5 complexes are reported. Fragmentation behavior common to all the studied compounds is noted, as well as some ligand‐specific fragmentation. Fragment ions associated with ligand recoordination, ligand substituent transfer and inter‐ligand bond formation are noted. The role of the electron density around the metal center, and in particular the ‘18‐electron’ configuration, on the fragmentation of these compounds is discussed.
Mass spectra and stereochemistry of alkylsubstituted 2,2‐diphenyl‐1,3‐dioxa‐2‐germacyclohexanes
Authors: Gren A. I. , Yasinenko N. E. , Timofeev O. S. , Zagorevskii D. V.
Published: May 2005

The correlations between electron impact induced formation of fragment [M  C6H6]+˙ from alkyl‐substituted 2,2‐diphenyl‐1,3‐dioxa‐2‐germacyclohexane (1) and the peculiarities of the molecular structures were found. Benzene elimination is regiospecific and stereoselective, resulting from the abstraction of an axial phenyl group and a hydrogen atom from the C‐4 or C‐6 position of the ring.
Enhancement of negative ion currents by argon/CO2 mixtures in an electron impact ion source
Authors: Lauber R. , Schlunegger U. P.
Published: May 2005

Argon and mixtures of argon with carbon dioxide in the range of 1–50% have been used as moderator gases for negative ion production in an electron impact ion source of a VG ZAB‐2F mass spectrometer. The enhancement of quasi‐molecular anion ([M – H]−) currents of oxygen‐containing samples has been studied. It is a function of the composition of moderator gas mixture, moderator gas pressure, and sample pressure in the ion source. Most intensive quasi‐molecular anion currents have been observed at a pressure in the ion source of c. 2.5 × 10−5 Torr (measured by the ion gauge remote from the ion source of the ZAB‐2F) using a moderator gas mixture of 10% CO2 in argon. Fragmentation of the samples may be increased by increasing the concentration of CO2 in the moderator gas.
Ortho effect of the nitro group in the fragmentation of 1‐phenyl‐3‐nitrophenyl‐2‐pyrazolines
Authors: Srzić D.
Published: May 2005

Electron impact mass spectra and mass‐analysed ion kinatic energy spectra of the title compounds are discussed. The characteristic fragment ions of the ortho isomer are shown by high resolution and kinetic energy release measurements to involve the transfer of hydrogen to the nitro group and oxygen from the nitro group to the pyrazoline carbon.
Ammonia in the ion source. II. Clustering with aromatic nitro compounds
Authors: Gillis Richard G.
Published: May 2005

Under positive ion chemical ionization conditions with ammonla at relatively low pressure, aromatic nitro compounds do not form [M + H]+ ions but often form ionic clusters [M + NH4]+ and [M + N2H7]+. Nitrobenzene forms a cluster [2M + NH4]+ and aniline, formed by nucleophilic substitution, leads to a cluster [anilinium ion + nitrobenzene]+. The dinitrobenzenes form [M + NH4]+ clusters and show evidence of nitroaniline formation and clustering. 1,3,5‐Trinitrobenzene gives little indication of clustering or of substitution. The six isomers of trinitrotoluene appear to be stabilized by the methyl group and form clusters up to [M + N3H10]+. Nucleophilic substitution leads to dinitrotoluidines, which also form clusters with ammonium ions.
Mass spectra of isomeric monothiopyrophosphates
Authors: Kamiński R. , Paneth P. , Reimschüssel W.
Published: May 2005

The main fragmentation patterns of the phosphorus‐containing moiety of bis(5,5‐dimethyl‐2‐oxo‐1,3,2‐dioxaphosphorinanyl) sulphide, 3, and its isomer P‐oxo‐P'‐thiono‐bis(5,5‐dimethyl‐1,3,2‐dioxaphosphorinanyl) oxide, 4, are presented. Isotope studies with 18O, 36S, 34S and 2H indicate that compound 3 undergoes an extensive isomerization prior to fragmentation. The mechanism of this isomerization must involve interaction of at least two molecules, as shown by isotope scrambling experiments.