bluuebunny/crossref_metadata_2025 huggingface dataset:
The behaviour of stereoisomeric ions in the gas phase: 2—Negative and positive chemical ionization of cyclohexanehexacarboxylic methyl esters
Authors: Audisio Guido , Grassi Maria , Traldi Piero , Daolio Sergio
Published: May 2005

The positive ion chemical ionization (CI (isobutane)), negative ion chemical ionization (NICI) electron attachment (CH4, He) and NICI (OH−) spectra of the title compounds have been studied in detail with the aid of deuterium‐labelled derivatives. The obtained results show that under CI conditions the stereospecificity is retained. Interesting correlations with the condensed phase epimerization yields are emphasized.
Provitamin D and vitamin D isomerizations in the mass spectrometer. Translational energy release and collision‐induced dissociation studies
Authors: Zaretskii Z. V. I. , Kingston E. E. , Beynon J. H. , Lauber R. , Schlunegger U. P.
Published: May 2005

Collision‐induced dissociation mass‐analysed ion kinetic energy spectrometry and translational energy release studies have established that provitamin D3 (7‐dehydrocholesterol), provitamin D2 (ergosterol), vitamin D3 and vitamin D2 isomerizations in the mass spectrometer occur at the fragment ion level leading to [MH2OCH3]+ ions of identical structure. It was found that the reaction, [M]+˙→[MH2O]+˙, plays a central role in these isomerizations.
Doubly charged ion mass spectra of organophosphorus compounds
Authors: Appling J. R. , Burdick G. W. , Moran T. F.
Published: May 2005

Doubly charged ion mass spectra have been obtained for 11 organophosphorus compounds. Methane has been used as a target gas to increase the probability of single electron transfer collisions in the first field‐free region of an Hitachi RMU‐7L mass spectrometer. In general, the spectra of organophosphorus compounds do not exhibit molecular ions but are dominated by fragment ions, many of which must be formed by rearrangement processes. A geometry‐optimized self‐consistent field molecular orbital method has been employed to compute energies and structural parameters for prominent ions. In addition, a diabatic curve crossing model has been used to examine the single electron transfer reactions responsible for intense ions in the doubly charged ion mass spectra. Appearance energies measured for ions prominent in the 2E spectra of organophosphorus compounds have ranged from 23 to 38 eV.
Fast atom bombardment mass spectrometry of coordination compounds
Authors: Bojesen Gustav
Published: May 2005

It is shown that fast atom bombardment mass spectrometry is well suited for the study of coordination compounds.
Chemical ionization mass spectrometry of doxylamine and related compounds
Authors: Korfmacher Walter A. , Holder Claude L. , Freeman James P. , Mitchum Ronald K. , Gosnell Aubrey B.
Published: May 2005

The chemical ionization mass spectrometric (CIMS) analysis of doxylamine, N,N‐dimethyl‐2‐[1‐phenyl‐1‐(2‐pyridinyl)ethoxy]ethanamine, and related compounds, using both ammonia and methane as reagent gases, is discussed. The two reagent gases did not produce the same major fragment ion for doxylamine. Mechanisms for the fragmentation of doxylamine under either ammonia or methane CIMS conditions are proposed. The mechanisms explain the observation of an m/z 182 fragment ion for doxylamine analyzed under methane CIMS conditions and an m/z 184 product ion detected under ammonia CIMS conditions.
Translational energy release and stereochemistry of steroids 6—Contribution of the 18‐ and 19‐methyl groups to the translational energy release for the angular methyl loss in unsaturated steroids
Authors: Zaretskii Z. V. I. , Kustanovich Z. , Kingston E. E. , Beynon J. H. , Lauber R. , Schlunegger U. P. , Djerassi Carl
Published: May 2005

The translational energy, T, released during angular methyl loss from the molecular ions of unsaturated steriod hydrocarbons and alcohols, containing the double bond in the position allylic to either the 19‐CH3 or 18‐CH3 group, has been measured. The different contributions of the two angular methyl groups to the overall T value for the [M]+˙→[MCH3]+ reaction are discussed.
The unimolecular dissociation of protonated phenyl ethers formed by chemical ionization
Authors: Meyrant Philippe , Flammang Robert , Maquestiau André , Kingston Eric E. , Beynon John H. , Liehr Joachim G.
Published: May 2005

A series of phenyl ethers with cyclic and acyclic olefins has been observed to form proton‐bound complexes on protonation under chemical ionization conditions with methane as the reagent gas. The competitive dissociations of these complexes have been studied by ion kinetic energy spectrometry and the measured branching ratios have been correlated with the relative stabilities of the product species.
Mass spectrometric studies on cyclo‐ and poly‐phosphazenes: 4—Attempts at mass spectrometrically induced polymerization of cyclotriphosphazenes substituted with primary and secondary amines
Authors: Gleria Mario , Audisio Guido , Daolio Sergio , Vecchi Enrico , Traldi Pietro
Published: May 2005

In this paper, the mass spectrometric behaviour of cyclophosphazenes substituted with primary and secondary amines is investigated, together with the mass spectrometric polymerization pattern of these compounds. While it is not possible to achieve the mass spectrometric polymerization of hexa(anilino)cyclotriphosphazene, ion–molecule reactions take place in the case of hexa(piperidino)‐ and hexa(morpholino)cyclotriphosphazenes, which lead to the formation of hexameric species. Evidence is given that pentasubstituted cyclophosphazenephosphorus cations are the species responsible for the oligomerization process.
Mass spectra of some high molecular weight tetra(alkyl)silanes
Authors: Onopchenko Anatoli , Sabourin Edward T. , Danner David A.
Published: May 2005

The mass spectra of tetra(alkyl)silanes having one short and three long alkyl groups were recorded (C20C32). These silanes did not give molecular ions, and the dominant course of fragmentation involved the loss of alkyl groups, followed by elimination of alkenes. The loss of alkyl groups, followed by elimination of alkenes. The loss of alkyl groups followed the sequence iso‐Pr>Et, Pr,… C14H29» Me. With alkyl groups longer than hexyl, a rearrangement was observed in which n‐alkanes were eliminated from the base ion. When the alkyl group was hexyl, the alkane eliminated was methane; when the alkyl group was heptyl, ethane was expelled; with octyl, it was propane; and with decyl, n‐pentane was expelled. Deuterium labeling showed that at least two modes of rearrangement were occurring.
Substitution reactions under NH3 chemical ionization conditions in cis‐/trans‐1,2‐dihydroxybenzosuberans
Authors: Madhusudanan K. P. , Prasad Mohan , Rastogi Shri Nivas , Fraisse D.
Published: May 2005

The nucleophilic substitution reaction under NH3 chemical ionization (CI) conditions in cis‐ and trans‐1,2‐dihydroxybenzosuberans (1–4) has been studied with the help of ND3 CI and metastable data. The results indicate that in the parent diols 1 (cis) and 2 (trans), the substitution ion [MsH]+, is produced mainly by the loss of H2O from the [MNH4]+ ion (SNi reaction) while in their 7‐methoxy derivatives 3 and 4, the ion‐molecule reaction between [MOH]+ and NH3 seems to be the major pathway for the formation of [MsH]+. The substitution ion from 1 and 2 and the [MH]+ ion from trans‐1‐amino‐2‐hydroxybenzosuberan give similar collision‐induced dissociation mass‐analysed ion kinetic energy spectra. Interestingly, their diacetates do not undergo the substitution reaction.
Mass spectra of phenoxyacetyl derivatives
Authors: Vairamani M. , Ishratullah K. , Reddy D. M. , Rao G. K. Viswanadha
Published: May 2005

The electron‐impact‐induced mass spectra of substituted N‐phenylphenoxyacetamides are discussed. The structure of the rearrangement ion at m/z 108 is investigated and compared with the molecular ion of anisole by metastable ion and corrected collisionally activated dissociation spectra.
The effect of para‐substitution on the mass spectra of arylsulphonate esters of neopentanol
Authors: Mamer Orval A. , Padmapriya Abeysinghe A. , Just George
Published: May 2005

The mass spectra of several para‐substituted benzenesulfonic and benzoic esters of unlabelled and 1,1‐d2‐neopentyl alcohol are examined and compared. Evidence is presented of migration of the aryl group from the sulfur to an oxygen atom in the molecular ions of the sulfonic esters. The nature of the fragmentation processes and the occurrence of metastable ions for these processes are both much more dependent upon the polarity of the para substituent in the case of the sulfonates than for the benzoates. Elimination of C5H10 occurs from the molecular ion of the p‐methoxysulfonate with transfer to the residual ion of a hydrogen atom selected randomly from the alkyl fragment, while in the case of the p‐aminosulfonate, incomplete randomization is demonstrated.
Stereoisomeric effects on mass spectral fragmentations of chloronorbornanones
Authors: Rothwell A. P. , Cooks R. G. , Singh T.‐V. , De Cárdenas L. , Morrison H.
Published: May 2005

Stereoelectronic factors allow facile Cl˙ atom loss from the exo‐6‐chloro‐2‐norbornanone radical cation but not from the endo‐6‐epimer. The predominant primary reaction in the endo‐6 and in the exo‐5 and endo‐5 compounds is HCl elimination. While CI˙ elimination occurs with skeletal reorganization, HCl loss, at least in part, does not. The 5‐chloro isomers undergo a regiospecific McLafferty rearrangement which occurs relatively slowly in competition with Cl˙ and HCl loss. The use of energy‐resolved forms of tandem mass spectrometry provides considerable detail regarding the unimolecular fragmentations of these gaseous ions.
Identification of two separate mechanisms for HCN loss from gas phase quinoline cations
Authors: Baldwin Michael A. , Langley G. John
Published: May 2005

Critical energy measurements on 13C‐labelled quinolines show that the energy requirement for elimination of H(C‐2)N from metastable ions is lower than that for H(C‐3)N elimination, the critical energies being 4.03 ± 0.05 eV and 4.17 ± 0.05 eV, respectively. It is also shown that involvement of C‐2 and C‐3 in unimolecular HCN elimination from ions in the second field‐free region is greater, by factors of approximately 3 and 2 respectively, than would be anticipated for elimination following complete carbon randomization.
Mass spectra of 1‐(2′‐hydroxy‐5′‐alkylphenyl)‐1‐alkanone (E)‐oximes
Authors: Łozyński Marek , Krzyzanowska Ewa
Published: May 2005

The mass spectra of 1‐(2′‐hydroxy‐5′‐alkylphenyl)‐1‐ethanone (E)‐oximes 1–6 and 1‐(2′‐hydroxy‐5′‐methylphenyl)‐1‐alkanone (E)‐oximes 7–12 are given and the major fragmentation pathways discussed. The simultaneous loss of water and alkyl moieties from the molecular ion indicates that a skeletal rearrangement take place and a cycloheptatrienyloheterocyclic system is formed. The McLafferty rearrangement, γ‐fission in the side aliphatic chain and oxygen expulsion are discussed with evidence being drawn from accurate mass measurements, metastable ions and comparison with mass spectral data of related compounds.
Proton affinities by reactant ion monitoring: Triphenyl group Va compounds
Authors: Tran Vinh Thi , Munson Burnaby
Published: May 2005

Proton affinities of a series of triphenyl Group Va compounds have been determined by bracketing using reactant ion monitoring: (C6H5)3N = 904 ± 8 kJ mol−1, (C6H5)3P = 968 ± 5 kJ mol−1, (C6H5)3As = 904 ± 8 kJ mol−1 and (C6H5)3Sb = 846 ± 8 kJ mol−1. The large difference in substituent effect of phenyl for hydrogen between As or P and N may result from overlap of the 2p orbitals of N with the sp2 orbitals on the ring carbons and lack of overlap for P or As. Proton affinities of phenylalkylphosphine oxides are essentially the same, 904 ± 8 kJ mol−1, independent of alkyl group.
Electron impact and ammonia chemical ionization mass spectra of n‐azabicyclo[m.2.0]alkan‐(n + 1)‐ones (m = 3–6, n = 6–9)
Authors: Pihlaja Kalevi , Vainiotalo Pirjo , Bernáth Gábor , Göndös György , Gera Lajos
Published: May 2005

Electron impact induced fragmentation of the title compounds obeys a route where the lactam moiety, OCNH, is cleaved first, with the accompanying formation of a cycloalkene ion. This can be verified by low‐resolution, high‐resolution, B/E and B2/E spectra as well as by collisional activation spectra of, for example, the ions m/z 82 and 67 from 7‐azabicyclo[4.2.0]octan‐8‐one and from cyclohexene. The only, and fairly weak, fragment ions including O and N are [C3H3O]+, [CkH2k‐2N]+ (k = 5–8) and [C3H6N]+. The ammonia chemical ionization spectra are also characteristic for all four lactams and show the same dominant ions in all cases, namely [M + 1]+, [M + 1 + NH3]+˙ and [2 M + 1]+˙.
Laser desorption mass spectrometry of squaric acid and its salts
Authors: Byrd Gary D. , Fatiadi A. J. , Simons D. S. , White V E.
Published: May 2005

The laser desorption mass spectrometry of the oxocarbon squaric acid (3,4‐dihydroxy‐3‐cyclobutene‐1,2‐dione) and its salts of the form A2C4O4 (A = cation) is described. Both positive and negative ion spectra were obtained. The positive ion spectrum of the acid is characterized by an ion corresponding to loss of CO from [M + H]+. The negative ion spectrum shows an intense [M − H]− peak in addition to a dimer species. The alkali salt spectra contain [M + A]+ in the positive mode and [M − A]− and an intense [C4HO4]− in the negative mode. The smaller alkali salts also have an [M + H]+ adduct ion. Unlike the alkali squarates, the ammonium salt shows ions corresponding to losses of neutrals from the molecular adduct in the positive ion spectrum and a dimer species in the negative ion spectrum. Molecular weight information was obtained in all cases. A (bis) dicyanomethylene derivative of potassium squarate was also studied. Some field desorption mass spectrometry results are presented for comparison.
Mass spectra of some 2‐(4′‐butyl‐3,′5′‐dimethylpyrazol‐1′‐yl)‐6‐substituted benzothiazoles
Authors: Singh Shiv P. , Vaid Radhe K.
Published: May 2005

The fragmentation of the title compounds on electron impact has been studied and the major processes interpreted. The base peak invariably appears at [M  43]+ whose origin from the butyl chain has been traced with the help of metastable ion studies and accurate mass measurements. Loss of methyl cyanide, involving the decomposition of the pyrazole moiety, is observed only from the fragment ions.
Ortho effects in organic molecules on electron impact 13—mechanism of decarboxylation in o‐carboxy heteroaromatics
Authors: Ramana D. V. , Kartha T. R. Gopinathan
Published: May 2005

Expulsion of CO2 from the molecular ions of the 2‐(2‐carboxyphenyl) derivatives of benzoxazole, benzothiazole and benzimidazole gives rise to the base peaks on electron impact. The proposed mechanism for this fragmentation process, involving the anchimeric assistance of the heteroatom by the initial abstraction of the H˙ from the carboxyl group followed by the expulsion of CO2 from the molecular ions, is supported by the study of the linked scan spectra.
Structure analysis of the propionic–pentafluoropropionic anhydride derivatives of norepinephrine and serotonin
Authors: Barker Steven A. , Tolbert Lelland C. , Brown George B.
Published: May 2005

Gas chromatographic/mass spectrometric analysis was used for the examination of norepinephrine and serotonin derivatives formed from their sequential reaction with propionic anhydride and pentafluoropropionic anhydride. The structures of the resulting derivatives were determined by the analysis of the mass spectra of the proteo and deutero homologs and by nuclear magnetic resonance spectroscopy. Mechanisms for the synthesis and electron impact fragmentation of these derivatives are proposed.
Mass spectrometry of analogues of pyrimidine bases: 2‐ and 4‐alkylthio‐5‐halogenouracils
Authors: Stobiecki Maciej
Published: May 2005

The electron impact induced mass fragmentations of 16 new 2‐ and 4‐alkylthio‐5‐chloro‐ and 2‐ and 4‐alkylthio‐5‐bromouracils are presented. The elucidation of the fragmentation pathways is described. The fragmentation routes have been confirmed by accurate mass measurements and metastable transitions. It has been found that the position of uracil ring thiation may be deduced on the basis of the mass spectral fragmentation patterns.
Electron impact mass spectrometry of some 2‐methyl‐2‐aryl‐ and 2‐methyl‐2‐alkyl‐1,3‐dithianes
Authors: Sturaro Alberto , Traldi Pietro
Published: May 2005

The electron impact mass spectrometric behaviour of four 2‐methyl‐2‐aryl‐ and two 2‐methyl‐2‐alkyl‐1,3‐dithianes is described and discussed in detail, with the aid of exact mass measurements, linked scans and mass‐analysed ion kinetic energy spectrometry. The mechanism of the primary HS2˙ loss, as well as those of the more unusual fragmentation pathways, are given.
Deuterium isotope effects and mechanism of the gas phase reaction [C3H7]+→[C3H5]+ + H2
Authors: Hvistendahl Georg , Uggerud Einar
Published: May 2005

The deuterium kinetic isotope effect and the deuterium isotope effect upon kinetic energy release have been calculated for the loss of H2 from the [C3H7]+ ion. The calculations are based on the transition state structure suggested recently from ab initio calculations on the reaction pathway. The results obtained are in good agreement with experimental data.
Bifunctional even‐electron ions. II. Fragmentation behaviour of aliphatic ω‐hydroxy and ω‐methoxy methoxonium ions
Authors: Záhorszky U. I.
Published: May 2005

Bifunctional methoxonium ions \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm R} -\mathop {\rm C}\limits^ + ({\rm OCH}_3 ) - ({\rm CH}_2 )_{\rm n} - {\rm OH}({\rm b}) $\end{document} and \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm R} - \mathop {\rm C}\limits^ + ({\rm OCH}_3 ) - ({\rm CH}_2 )_{\rm n} - {\rm OCH}_3 ({\rm c}) $\end{document} (c) show as the main reactions those caused by functional group interaction, as has already been found for the analogous hydroxonium ions (g). Although there are similarities in the fragmentation behaviour of the isomeric ions b and g, their fragmentation pathways are different, proving b and g as distinct species. The dominant primary fragmentation for b and c is loss of CH3OH. The hydrogen migrations prior to this reaction have been established by deuterium labelling. The findings on the fragmentation behaviour of the bifunctional methoxonium ions have been extended to the general behaviour of hydroxy and alkoxy substituted alkoxonium ions.
Electron impact and chemical ionization mass spectra of bis(methoxycarbonyl) [2.2](2,5)pyridinophanes. Formation of quinolizinium ions under electron impact
Authors: Rentzea Marina , Hasselbach Hans‐Joachim , Staab Heinz A.
Published: May 2005

For four isomeric bis(methoxycarbonyl)[2.2](2,5)pyridinophanes differing only in the mutual orientation of the two nicotinic ester units, electron impact mass spectra were measured. The fragmentations observed distinguish surprisingly well between the isomers, depending on the transannular substitution pattern. Of special interest is that for one isomer the otherwise unimportant ion at m/z 298 is found as base peak. This ion is formed by expulsion of HCN from the molecular ion, transannular cycloaddition and aromatization to a stable quinolizinium ion. Fragmentation pathways of the isomers are compared, and chemical ionization and negative ion chemical ionization mass spectra are discussed.
Carbanion rearrangements: Collisionally activated dissociations of deprotonated alkyl malonates
Authors: Hayes Roger N. , Bowie John H.
Published: May 2005

The major fragmentations observed in the collisionally activated mass spectra of secondary and tertiary carbanions from malonate esters are quite different. For example, the major fragmentation by deuterium labelling where appropriate.
Mass spectrometric synthesis—III Gas phase ion/molecule reaction between benzoic acid and some substituted phenols
Authors: Podda Gianni , Maccioni Antonio , Sturaro Alberto , Traldi Pietro
Published: May 2005

The reaction of benzoic acid with some substituted phenols, carried out in the chemical ionization source of a mass spectrometer and under high pressure conditions leads to phenyl benzoate. This has been proved by accurate mass measurements and collision activated dissociation mass‐analysed ion kinetic energy spectra. The intimate mechanisms of this reaction are discussed in detail.
A mass spectral study of stable neutral enols
Authors: Peake D. A. , Stanley J. , Kingsbury C. A. , Gross M. L.
Published: May 2005

The high‐resolution mass spectra of two stable enol tautomers, 4,6‐diethanoyl‐1‐methyl‐5‐phenyl‐3‐cyclohex‐ene‐1,3‐diol (2) and 4‐ethanoyl‐5‐hydroxy‐2‐(1‐hydroxyethylidene)‐5‐methyl‐3‐phenylcyclohexanone (3), and the corresponding diketone tautomer, 2,4‐diethanoyl‐5‐hydroxy‐5‐methyl‐3‐phenylcyclohexanone (1), are reported. Collisional activation of the molecular ions and major ionic fragments is used to assign decomposition pathways and to compare ion structures. Ionized 1 and 2 do not interconvert by a keto‐enol tautomerism, but isomerize to a common intermediate. This isomerization probably involves opening of the cyclohexanone ring and transfer of the enolizable hydrogen, and is followed by elimination of water. The radical cation of 3 does not interconvert with [1]+˙ and [2]+˙ Instead, [3]+˙ dissociates by loss of an acetyl radical and eliminates water via a higher‐energy pathway. As a result, the mass spectra of 1 and 2 are similar, whereas the mass spectrum of 3 is unique.
Thermospray ionization and tandem mass spectrometry of dyes
Authors: Ballard John M. , Betowski Leon D.
Published: May 2005

Sixteen commercial dye samples and three liquid wastes from organic pigment and dye manufacture have been characterized without prior chromatography by thermospray ionization and low energy collision‐activated dissociation of protonated molecules using a triple quadrupole mass spectrometer. Many samples contained precursors of the dyes and other by‐products of the synthesis. Many of these components were identified by collision‐activated dissociation experiments and by inspection of the chemistry of dye manufacture. Detection limits of 20–200 ng in the positive ion mode were obtained for seven dyes of the anthraquinone, triarylmethane, xanthene, coumarin, azo and sulfonated azo dye classes. Under conditions of negative ionization, detection limits for an anthraquinone dye and a sulfonated azo dye were about one order of magnitude higher.
The involvement of neutral species in the NO− → O+ charge inversion reaction
Authors: Kingston R. G. , Brenton A. G. , Guilhaus M. , Beynon J. H.
Published: May 2005

Intermediates in the overall charge inversion reaction NO− → O+˙ (la), have been found to be O and NO˙ neutrals, and NO+ ions. The intermediates involved have been characterized by various mass spectrometric techniques; for example, inducing the steps of the reaction in separate field‐free regions allows the peaks for the consecutive reactions NO− → NO+ → O+˙ (II) to be recorded free from interference. However, to observe the involvement of a neutral intermediate, techniques such as floating the collision cell and applying a voltage to a deflector plate in front of the collision cell have been employed. Utilizing these methods allows a peak to be obtained due to one or both of the processes, NO− → NO˙ → O+˙ (IIIa) and NO− → O+˙ (IIIb), which cannot be separated. It is shown that the peak for the overall reaction NO− → O+˙ can be modelled and reconstructed by addition of peaks, in a ratio of 1:3, produced by reactions II and III. This provides a reasonable account of the peak shape, in particular, of the tails of the peak which correspond to fragmentations involving large translational energy releases of up to 10 eV.
Ionization by fast atom bombardment—A chemical lonization (matrix) process in the gas phase?1
Authors: Schröder E. , Münster H. , Budzikiewicz H.
Published: May 2005

It is proposed that ion formation from non‐ionic substrates under fast atom bombardment occurs essentially by chemical ionization in the gas phase by a matrix plasma. Corroborating experiments regarding the matrix plasma are presented.
Structures of gas phase C5H8 radical cations: A collisional ionization study
Authors: Dass Chhabil , Peake David A. , Gross Michael L.
Published: May 2005

Collisional ionization (charge stripping) and charge exchange ionization spectrometry were utilized to determine structures of fourteen cyclic and acyclic C5H8 radical cations, including ionized 1,2‐ 1,3‐, 1,4‐ and 2,3‐pentadienes (‐PD), isoprene, 1‐ and 3‐methylcyclobutenes (1‐ and 3‐MCB), 3‐methyl‐1,2‐butadiene (3‐M‐1,2‐BD), methenecyclobutane (MECB), cyclopentene, 3‐methyl‐1‐butyne (3‐MB), 1‐ and 2‐pentynes and vinylcyclopropane (VCP). The pressure of the charge exchange reagent gas in the ion source was adjusted to generate ions of different energy contents. The structures of the C5H8 ions are energy dependent, and their isomerization reactions can be monitored as a function of the amount of internal energy deposited by charge exchange. 1,3‐PD, isoprene and cyclopentene radical cations are identified as stable ion structures. 1‐MCB, 3‐M‐1,2‐BD and 3‐MB radical cations isomerize to isoprene ions, whereas ionized VCP, 3‐MCB, 1,2‐PD, 2,3‐PD, 1,4‐PD, 1‐pentyne and 2‐pentyne ultimately isomerize to the [1,3‐PD]+˙. Thermodynamic arguments are invoked to corroborate these isomerization reactions. The critical energies of the isomerizations are also estimated.
Electron impact and chemical ionization mass spectra of 2,2‐diphenyl‐3‐arylcyclobutanone oximes. Formation of ion m/z 167
Authors: Sudhakar Reddy G. , Smith Grant Gill
Published: May 2005

The electron impact (EI) and chemical ionization (CI) spectra of 2,2‐diphenyl‐3‐aryl cyclobutanone oximes (1–5) are reported. Formation of diphenylmethyl cation at m/z 167 is a major fragmentation process in both EI and CI spectra. Labelling studies established that the hydrogen involved in this rearrangement transfers from the NOH group and not from cyclobutane ring positions. The [M + 3]+ ions are formed under CI conditions as a result of CN double bond reduction. An interesting secondary kinetic isotope effect is observed in the formation of ion e at m/z 183 in both EI and CI spectra. Other characteristic fragmentation pathways occurring in the EI and CI spectra of these compounds are outlined.
Gas phase glycosidic cleavage of oxynions from alkyl glycosides
Authors: Prome Jean‐Claude , Aurelle Hélène , Prome Danielle , Savagnac Arlette
Published: May 2005

The oxyanion [MH]− from several methylglycosides were generated by fast atom bombardment and their decomposition was studied by mass‐analysed ion kinetic energy spectrometry. The main decomposition pathway is the loss of methanol. The hydroxylic hydrogen arises by proton transfer from the hydroxyl groups of the sugar. In the gluco‐series, no anomeric effect is found. The absence of either the hydroxyl groups at C‐2 or C‐6 does not inhibit the glycosidic cleavage. However, the blocking of both the hydroxyl groups at C‐4 and C‐6, by a benzylidene group or two methyl groups, inhibit completely the glycosidic cleavage. From these results, it is proposed that the glycosidic cleavage occurs after opening the sugar ring by a vicinal attack of an oxyanion at C‐6 or C‐4 to the C‐5 carbon atom. Then, the ionized hemi‐acetals fragment into a methanolate anion and a 5,6‐ or 4,5‐anhydrosugar which exchange another proton before their separation into charged and neutral species.
Electron impact mass spectra of some new macropolycycles
Authors: Constantin E. , Kotzyba‐Hibert F. H. , Lehn J. M. , Traldi P.
Published: May 2005

Mass spectra of some macropolycycles have been studied. Normal and metastable (B/E) mass spectra are presented. The fragmentation patterns and the structures of the main ions are discussed.
Charge transfer reactions of organic ions containing oxygen: Correlation between reaction energetics and cross sections
Authors: Shields G. C. , Steiner P. A. , Nelson P. R. , Trauner M. C. , Moran T. F.
Published: May 2005

Cross sections for charge transfer reactions of organic ions containing oxygen have been obtained using time‐of‐flight techniques. Charge transfer cross sections have been determined for reactions of 2.0 to 3.4 keV ions produced by electron impact ionization of oxygen containing molecules such as methanol, ethanal and ethanol. Experimental cross section magnitudes have been correlated with reaction energy defects computed from ion recombination energies and target ionization energies. Large cross sections are observed for reacting systems with small energy defects.
Laser desorption fourier transform mass spectra of ascorbic and isoascorbic acids
Authors: Coad Peter , Coad Raylene A. , Yang Cathy L. C. , Wilkins Charles L.
Published: May 2005

Positive and negative ion laser desorption Fourier transform mass spectra of ascorbic acid, isoascorbic acid, and their sodium and potassium salts have been determined. A number of differences between these spectra and previously reported laser microprobe mass analyzer (LAMMA) spectra are found. In contrast with earlier results, m/z 175 anions are present in all negative ion spectra, as are cluster ions. Thus, it should not be concluded that the radical salts are electroneutral, as claimed in the earlier study.
Electron impact induced fragmentations of some 2,2‐disubstituted 1,3‐dithiolanes
Authors: Vainiotalo Pirjo , Nevalainen Vesa
Published: May 2005

Electron impact induced fragmentations of the title compounds were studied by exact mass measurement and metastable ion analysis. Sulphur atoms within the ring effectively stabilize the positive charge. In most cases the loss of the larger substituent, and not the other, methyl group, gives rise to the base peak in the spectrum. Examination of competing metastable transitions shows that generally this is also the lowest activation energy primary process. In general primary ring cleavage reactions are not important unless there is a heteroatom in the substituent that can assist this cleavage.
The reactions of the ions [XC]+, [X2C]+·, [X3C]+· and [X4C]+· (where X = H or F) with ethene and propene
Authors: Robinson J. N. , Tedder J. M.
Published: May 2005

The reaction of C1 ions with ethene and propene has been studied in the gas phase using a triple quadrupole mass spectrometer.
On the origin of the peaks of some substituted ions in the mass spectra of lecithins
Authors: Constantin E. , Traldi P.
Published: May 2005

Preliminary results concerning the origin of the peaks of some substituted ions in the mass spectra of lecithins, obtained under electron impact and chemical ionization conditions, are reported.
Ion chemistry of α‐diazoketones. 1. A collissional activation study of 1‐diazo‐3‐phenoxypropan‐2‐one upon elecgtron impact
Authors: Selva Antonio , Ferrario Francesco , Saba Antonio
Published: May 2005

The gaseous ionic products of 1‐diazo‐3‐phenoxypropan‐2‐one upon electron impact show that cyclization reactions, which have counterparts in condensed‐phase chemistry, occur in competition with a mass spectral Wolff type rearrangement.
Structure and fragmentation of [C6H13O]+ ions formed by chemical ionization
Authors: Weiss Mathania , Crombie Richard A. , Harrison Alex. G.
Published: May 2005

The structure and fragmentation of eight [C6H13O] + ions formed by protonation of C6H12O carbonyl compounds in the gas phase have been investigated using isotopic labeling and metastable ion studies to investigate the fragmentation reactions and collisional dissociation studies to probe ion structures. Protonated 3‐methyl‐2‐pentanone and protonated 2‐methyl‐3‐pentanone readily‐interconvert by pinacolic‐retro‐pinacolic rearrangements; the remaining six ions represent stable ion structures, although in many cases fragmentation is preceded by pinacolic‐type rearrangements. Unimolecular (metastable ion) fragmentation of the [C6H13O] + species occurs by elimination of H2O, C3H6, C4H8 and C2H4O. The last three elimination reactions appear to occur through the intermediacy of a proton‐bound complex of a carbonyl compound and an olefin, with the proton residing with the species of higher proton affinity on decomposition of the complex.
Mass spectrometry of 1,3,4‐thiadiazolo thiacrown ethers
Authors: Pappalardo Sebastiano , Occhipinti Salvatore
Published: May 2005

The mass spectra of two homologous series of 1,3,4‐thiadiazolo thiacrown ethers possessing one or two heterocyclic subunits, respectively, have been correlated and compared with those of closely related open‐chain analogues. The prevailing feature in the spectra of these macrocycles is the presence of homologous series of ions, which formally correspond to the sequential loss of C2H4O units from appropriate precursors. The majority of these ions have been rationalized in terms of structure and mechanism of formation by assuming an electron impact induced isomerization process (via H migration) of the molecular ion to several competing linear structures prior to fragmentation. Metastable peak analysis and high‐resolution measurements provide support for the postulated fragmentation mechanisms and product ion structures.
Multidimensional computer evaluation of mass spectra
Authors: Neudert R. , Bremser W. , Wagner H.
Published: May 2005

The increasing importance of spectroscopic methods as an analytical tool in industry, combined with the trend to automatize spectrometers, demands new standards in the quantity and quality of spectrum interpretation. Suitable computer programs should be able to predict structural features from mass spectral properties. The knowledge base is a structure‐oriented mass spectral data collection consisting of some 42000 spectra and topologies. The comparison of selected mass spectral properties such as similarity, neutral losses and ion series of the unknown with the equivalent properties of the library spectra results in a set of corresponding structures. Subsequent substructure analysis yields a histogram of substructure frequencies containing information about their statistical relevance. The relevant substructure set may be recombined to produce a structure proposal, as is demonstrated for 1‐acetyl‐2‐methoxy‐4‐trimethylsilyioxybenzene. In a second example, the relevant substructures derived by the interpretation system are used as input for the 13C‐NMR substructure generator. This procedure reduces the solution space of the structure prediction algorithm considerably. Besides the spectrum interpretation, additional possibilities are available. The substructure search enables us, for example, to look for mass spectrometric reaction centres. Beyond that, substructure analysis is applicable to the determination of structural features typical of certain combinations of neutral losses and/or characteristic fragments.
The chemical ionization mass spectra of 2‐tert‐butyl‐substituted 1,3‐cycloalkanediol diacetates and dimethyl ethers
Authors: D'Haenens L. , Van De Sande C. C. , Schelfaut M. , Vandewalle M.
Published: May 2005

The chemical ionization (CI) mass spectra of the 2‐tert‐butyl‐substituted 1,3‐cyclopentane‐ and 1,3‐cyclohexanediol diacetates and dimethyl ethers have been determined using isobutane and methane as reagent gases. From the differences in the spectra of these compounds, it clearly follows that steric and conformational effects are expresssed in the CI mass spectra. The relative impact of these effects, however, is strongly dependent on diol derivatization and 2‐alkyl substitution.
Chemical ionization mass spectrometry with amines as reactant gases. V—Amine chemical ionization mass spectrometry of flavonoid glycosides
Authors: Mollova N. N. , Bankova V. S. , Popov S. S.
Published: May 2005

The chemical ionization mass spectra of flavonoid glycosides (O‐glycosides, C‐glycosides and acetylated glycosides) have been investigated. Triethylamine, ethylenediamine, diethylamine, methylamine and ammonia were used as reactant gases. The fragmentation mechanism is discussed, and the perspectives for establishing the molecular weights of glycosides, aid the nature of both the sugar residue and the aglycone, are outlined.
Destabilized carbenium ions. Secondary and tertiary α‐acetylbenzyl cations and α‐benzoylbenzyl cations
Authors: Dommröse Anne‐Marie , Grützmacher Hans‐Friedrich
Published: May 2005

The secondary α‐acetylbenzyl and α‐benzoylbenzyl cations, as well as their tertiary analogues, have been generated in a mass spectrometer by electron impact induced fragmentation of the corresponding α‐bromoketones. These ions belong to the interesting family of destabilized α‐acylcarbenium ions. While primary α‐acylcarbenium ions appear to be unstable, the secondary and tertiaiy ions exhibit the usual behaviour of stable entities in a potential energy well. This can be attributed to a ‘push‐pull’ substitution at the carbenium ion centre by an electron‐releasing phenyl group and an electron‐withdrawing acyl substituent. The characteristic unimolecular reaction of the metastaible secondary and tertiary α‐acylbenzyl cations is the elimination of CO by a rearrangement reaction involving a 1,2‐shift of a methyl group and a phenyl group, respectively. The loss of CO is accompanied by a very large kinetic energy release, which gives rise to broad and dish‐topped peaks for this process in the mass‐analysed ion kinetic energy spectra of the corresponding ions. This behaviour is attributed to the rigid critical configuration of a corner‐protonatei cyclopropanone derivative and a bridged phenonium ion derivative, respectively, for this reaction. For the tertiary α‐acetyl‐α‐methylbenzyl cations, it has been shown by deuterium labelling and by comparison of collisional activation spectra that these ions equilibrate prior to decomposition with their ‘protomer’ derivatives formed by proton migration from the α‐methyl substituent to the carbonyl group and to the benzene ring.
Studies in chemical ionization mass spectrometry part. XVI: Are the reactions of aliphatic cc double bonds with NO+ governed by remote functional groups?
Authors: Budzikiewicz H. , Schneider B. , Busker E. , Boland W. , Francke W.
Published: May 2005

It is shown that the characteristic fragments observed by Malosse and Einhorn (Adv. Mass Spectrom. 1369 (1986)) in the CI(NO) spectra of alkenyl acetates and related compounds (cleavage of the double bond and formation of an acyl ion), which had not been reported, for alkenes and alkenoic acids, for example, are actually formed from all straight‐chain olefinic compounds (the only exceptions being where the double bond is too close to one of the ends of the chain). Their relative abundance may, however, vary from almost zero to 100%, and it is highly dependent on experimental parameters (e.g. the source temperature and even the type of instrument used). Apparent inconsistencies in the data reported in the literature could thus be resolved.
Electron impact mass spectrometry of hemiterpenoid tricyclic quinoline alkaloids
Authors: Sturaro Alberto , Traldi Pietro , Bravo Pierfrancesco , Viani Fiorenza , Resnati Giuseppe
Published: May 2005

The mass spectral behaviour of some quinoline‐type alkaloids, 3,4‐dihydro‐2H,5H‐pyrano[3,2‐c]quinolin‐5‐ones, isomeric 3,4‐dihydro‐2H,5H‐pyrano[2,3‐b]quinolin‐5‐ones and 2H,5H‐pyrano[3,2‐c]quinolin‐5‐ones, was studied in detail with the aid of linked scans, exact mass measurements and collisional spectrometry. The occurrence of a partial isomerization of the differently annulated isomers to a common, open‐chain structure is discussed.
Selective surface ionization of quaternary salts on a platinum filament
Authors: Van Gemmeren U. , Röllgen F. W.
Published: May 2005

Surface ionization of quaternary ammonium and pyridinium salts evaporated onto a platinum filament has been investigated. The experiments reveal a high selectivity for the formation of intact cations from these salts with virtually no fragmentation up to about 1000 K, and a low level of fragmentation up to about 1300 K, while even at higher temperatures the ionization of volatile non‐ionic compounds such as trialkyl amines is largely suppressed. The fragmentation of quaternary cations at higher temperatures is attributed in part to decomposition reactions in a two‐dimensional ion trap on the surface formed by the image force of the ions. For some compounds and mixtures, evidence is presented of the exchange of alkyl groups for cations as a thermal reaction prior to volatilization of the salts. The surface ionization technique appears promising for selective detection of quaternary salts from complex mixtures.
Mass spectral studies of naphthoflavones
Authors: Guidugli F. H. , Kavka J. , Garibay M. E. , Santillan R. L. , Joseph‐Nathan P.
Published: May 2005

The electron impact induced fragmentations of the five possible naphthoflavones have been studied with the aid of low‐ and high‐resolution measurements, metastable decompositions and isotope labelling using either deuterium or carbon‐13 atoms. All compounds show both the direct expulsion of a CO residue from the carbonyl group and the retro Diels–Alder cleavage. The abundant [M–H]+ ion has been formulated as the substituted β‐tropolone species, which, in the case of β‐naphthoflavone, is in competition with a pentacyclic species arising from the elimination of H‐5 as evidenced in the spectrum of 5‐d‐β‐naphthoflavone. Other previously unsuspected ions are also in evidence.
Selective reagents in chemical ionization mass spectrometry: Tetramethylsilane with aliphatic alcohols
Authors: Orlando Ron , Strobel Fred , Ridge D. P. , Munson Burnaby
Published: May 2005

Mixtures of tetramethylsilane and helium have been found to form [M + 73]+ adducts, hydrated trimethylsilyl ions and alkyl ions with aliphatic alcohols. The adduct ions were found to be formed by displacement of water from the hydrated trimethylsilyl ion. Ratios of the abundances of the adduct ions to the hydrated trimethylsilyl ion can be used to differentiate among primary, secondary and tertiary alcohols. Sensitivities for a number of alcohols with the tetramethylsilane/helium chemical ionization reagent system are approximately equal.
A metastable ion study of the electron impact fragmentation of some substituted 2,6‐pyrido‐containing crown ethers
Authors: Chen S. N. , Wang M. L. , Chen S. C. , Jing Z. Z. , Baldwin M. A. , Wu C. T. , Wang X. J.
Published: May 2005

Extensive networks of metastable ions link the major peaks in the electron impact mass spectra of two crown ethers containing 2,6‐pyrido units. High‐resolution mass measurements and the metastable peaks allow the elucidation of the fragmentation pathways. The spectra are influenced more by the presence of aromatic substituents than by the 2,6‐pyrido units.
Competing polar cycloreversion reactions under electron impact ionization in 3,4‐dihydro‐1,3,2‐oxazaphosphorin‐2‐oxides
Authors: Kulkarni P. S. , Sahasrabudhe S. D. , Tilak B. D.
Published: May 2005

The mass spectral fragmentation modes of a variety of substituted 3,4‐dihydro‐1,3,2‐oxazaphosphorin‐2‐oxides have been investigated. The ionic cycloreversions occur by two competing stepwise heterolytic cleavages, α and β to the phosphorus atom, producing heterodiene and heteropolarophile iminophosphorane ions. Substituents strongly influence the competitive fragmentation modes. Formation of heterodiene ion by retro‐Diels–Alder decomposition is preceded by hidden 1,3‐hydrogen shift and is the predominant proces in the metastable time region. Further fragmentation of the heterodiene ion occurs by electrophilic substitution‐elimination of the hydrogen atom.
Ring contractions of dihydro‐ and tetrahydro‐1,5‐benzodiazepines in electron ionization mass spectrometry
Authors: Chai Wen‐Gang , Wang Guang‐Hui , Jin Sheng , Lin Zu‐Ming , Liu Ping
Published: May 2005

Electron ionization mass spectra of a series of 2,4‐disubstituted dihydro‐ and tetrahydro‐1,5‐benzodiazepines are discussed. The fragmentation of these compounds is dominated by ring contractions of diazepine, which give both five‐ and six‐membered rings, benzimidazoles and quinoxalines. Tetrahydro compounds showed a tendency to eliminate one nitrogen from the ring system and give quinoline rings through NH2 and NH4 eliminations. The electron ionization spectra of cis and trans isomers of tetrahydro compounds are identical.
An attempt to distinguish between the components of a mixture of isomeric fragment ions
Authors: Bujtás György , Hollósi Miklós , Majer Zsuzsa
Published: May 2005

The [C7H10NO3]+ ion in the normal mass spectrum of 2‐ethoxycarbonyl‐5‐oxo‐2‐pyrrolidinepropanoic acid was shown to correspond to a mixture of two isomeric structures. By decreasing the ionizing electron energy, the one containing a CH2CH2COOH group becomes dominant. The proportion of the concentrations of the two isomeric ions was calculated by comparing their daughter ion spectra (obtained by linked scan at constant B/E) with the analogous spectra of a derivative partially labelled by deuterium at the carboxyl and amide groups.
Charge inversion and neutralization–reionization mass spectra of some alkoxide ions
Authors: Mercer Roger S. , Harrison Alex G.
Published: May 2005

The charge inversion mass spectra of C1 to C3 alkoxide ions have been obtained using He, N2 and O2 as collision gases. The three collision gases show similar efficiencies for collisional charge inversion and produce similar mass spectra, although fewer high‐energy oxenium ions are formed when O2 and N2 are used as collision gases. Using two collision cells and an intermediate deflector electrode the alkoxide ions have been neutralized in the first collision cell and the fast neutrals ionized in the second cell. The neutralization–reionization mass spectra obtained are similar to the direct charge‐inversion mass spectra indicating that mainly alkoxyl radicals are produced, although, depending on the neutralization collision gas and the alkoxide ion studied, other neutrals are formed in small yields. Deuterium isotopic labelling has been used to show that the main fragmentation reactions of the unstable oxenium ions formed involve 1,1‐elimination of H2 or an alkane.
Mass spectral study of bicyclic peroxides. 1. Dioxabicyclo[n.2.2]alkanes and the corresponding dioxabicyclo[n.2.2]alkenes
Authors: Mruzek Margaret N. , Bloodworth A. J. , Eggelte Henny J.
Published: May 2005

A series of dioxabicyclo[n.2.2]alkanes (n = 1,2,3 and 4) and dioxabicyclo[n.2.2]alkenes were studied under electron impact ionization. The fragmentation pathways were elucidated with the aid of accurate mass measurements, metastable scan techniojei and deuterium labelling. The preferential fragmentation of molecular ions in dioxabicyclo[n.2.2]alkanes corresponds to the loss of hydroperoxyl radical ·OOH. Hydrogens that are participating in this elimination come primarily from the syn position on the two‐membered carbon bridge. The dioxabicyclo[n.2.2]alkenes undergo the retro‐Diels–Alder process, which produces dioxygen and 1,3‐cycloalkadiene. In both saturated and unsatutated peroxides subsequent fragmentation of the hydrocarbon ring depends upon the value of n.
Gas‐phase protonation and methyl cation transfer from methyl halide ions
Authors: Houriet R. , Rolli E. , Flammang R. , Maquestiau A. , Bouchoux G.
Published: May 2005

The ion‐molecule reactions between [CH3X]+˙ [CH3XH] +, [CH3XCH3]+ ions (X = F, Cl, Br, I) and a number of nucleophiles have been studied by ion cyclotron resonance techniques. Protonation of the nucleophiles is observed to occur from both the molecular ions [CH3]X+˙ and protonated species [CH3XH]+ whereas dimethylhalonium ions [CH3XCH3]+ react principally by methyl cation transfer. A notable exception occurs in methyl iodide where the molecular ions [CH3I]+˙ act both as proton and methyl cation donors, whereas dimethyliodonium ions are found unreactive. The results are discussed with reference to the use of alkyl halides as reagent gases in chemical ionization experiments.
Endothermic proton transfer reactions from three [C6H6]+˙ isomers
Authors: Kinter Michael T. , Bursey Maurice M.
Published: May 2005

A triple quadrupole mass spectrometer was used to establish the proton affinities of phenyl, CH3CCCCCH3 and HCCCH2CCCH radicals as 870±29, 824±25, and 757±21 kJmol−1, respectively, from the kinetic energy of benzene, 2,4‐hexadiyne, and 1.5‐hexadiyne molecular ions at which the onset of proton transfer to less basic species occurs in the second rod assembly. These values were confirmed by other triple quadrupole experiments involving bracketing of exothermic proton transfers.