bluuebunny/crossref_metadata_2025 huggingface dataset:
Mass spectra of dicyanomethylene derivatives of benzophenone analogs
Authors: Wang Ching‐Bore , Her Guor‐Rong , Watson J. Throck
Published: May 2005

The dicyanomethylene derivative of a benzophenone analog significantly alters the fragmentation pattern observed during electron impact ionization of the underivatized parent compound. A double bond connecting the dicyanomethylene moiety to the parent compound is cleaved during a major fragmentation pathway for many of these compounds. A mechanism involving rearrangement of two hydrogen atoms is proposed to rationalize cleavage of this double bond. Conventional mass spectra as well as collisionally activated dissociation mass spectra of selected ions of several model compounds are reported and described in support of a proposed fragmentation mechanism.
The structure of decomposing [C7H7O]+ ions: Benzyl versus tropylium ion structures
Authors: Russell D. H. , Freiser B. S. , McBay E. H. , Canada D. C.
Published: May 2005

The unimolecular dissociation reactions for [C7H7O]+ ions generated by fragmentation of a series of precursor molecules have been investigated. The metastable kinetic energy values and branching ratios associated with decarbonylation and expulsion of a molecule of formaldehyde (CH2O) from the [C7H7O]+ ions are interpreted as the hydroxybenzyl and hydroxytropylium [C7H7O]+ not interconverting to a common structure on the microsecond time‐scale. In addition, similar measurements on protonated benzaldehyde, methylaryloxy and phenyl methylene ether [C7H7O]+ ions are interpreted as the dominant fraction of these decomposing ions having unique structures on the microsecond time‐scale. These results are supported by experimental heats of formation calculated from ionization/appearance energy measurements. The experimental heats of formation are determined as: hydroxybenzyl ions, 735 kJ mol−1; hydroxytropylium ions, 656 kJ mol−1; phenyl methylene ether ions, 640 kJ mol−1; methylaryloxy ions 803 kJ mol−1. The combination of the results reported in this paper with previously reported experimental data for stable [C7H7O]+ ions (see Ref. 1, C. J. Cassady, B. S. Freiser and D. H. Russell, Org. Mass Spectrom.) is interpreted as evidence that the relative population of benzyl versus tropylium [C7H7O]+ ion structures from a given precursor molecule is determined by isomerization of the parent ion and not by structural equilibration of the [C7H7O]+ ion.
Metastable decompositions of cyclopentanol ions and [C5H10O]+˙ ions with the oxygen on the first carbon
Authors: Hudson Charles E. , McAdoo David J.
Published: May 2005

Ionized cyclopentanol and [C5H10O]+˙ ions with the oxygen on the first carbon lose methyl, ethylene, ethyl, ethane and water in their metastable decompositions. We show by collisionally activated decompositions of the products that the losses of ethyl form CH3CH2CO+, the losses of ethylene form magnified image, and the losses of methyl probably yield magnified image. Deuterium labeling indicates that ethyl loss from ionized cyclopentanol occurs following α‐cleavage of the ring, isomerization to the enol isomer of ionized n‐pentanal and subsequent isomerization to the 3‐pentanone ion.
Fragmentations of 5,5‐diphenylmonothiohydantoins and their N‐ and S‐methyl derivatives after electron impact
Authors: Záhorszky U. I. , Nyitrai J. , Zauer K.
Published: May 2005

The mass spectra of 5,5‐diphenylmonothiohydantoins and their N‐ and S‐methyl derivatives have been investigated and interpreted in terms of structural correlations. All stable isomers can be easily distinguished by their fragmentation patterns.
Stereochemical applications of mass spectrometry. 3—Energy dependence of the fragmentation of stereoisomeric methylcyclohexanols
Authors: Harrison Alex G. , Lin Margaret S.
Published: May 2005

Breakdown graphs have been constructed from charge exchange data for the epimeric 2‐methyl‐, 3‐methyl‐ and 4‐methyl‐cyclohexanols. Although the breakdown graphs for epimeric pairs are essentially identical above ∼12 eV recombination energy, significant differences are observed for the epimeric 2‐methyl‐ and 4‐methyl‐cyclohexanols at low internal energies. For the 2‐methylcyclohexanols the ratio ([MH2O]+·/[M]+·)cis/([MH2O]+·/[M]+·)trans is 3.2 in the [C6F6]+· charge exchange mass spectra. This is attributed to both energetic and conformational effects which favour the stereospecific cis‐1,4‐H2O elimination for the cis epimer. The breakdown graph for trans‐4‐methylcyclohexanol shows a sharp peak in the abundance of the [MH2O]+· ion at ∼10 eV recombination energy which is absent from the breakdown graph for the cis epimer. This peak is attributed to the stereospecific cis‐1,4‐elimination of water from the molecular ion of the trans isomer; the reaction appears to have a low critical energy but a very unfavourable frequency factor, and alternative modes of water loss common to both epimers are observed at higher energies. As a result, in the [C6F6]+· charge exchange mass spectra the ([MH2O]+·/[M]+·)trans/([MH2O]+·/[M]+·)cis ratio is ∼24, compared to the value of 13 observed in the 70 eV EI mass spectra. No differences are observed in either the metastable ion abundances or the associated kinetic energy releases for epimeric molecules.
Electron impact mass spectra of 1,3,4‐thiadiazolo[3,2‐a]pyrimidin‐7‐one and isomeric‐5‐one derivatives
Authors: Foti S. , Russo F. , Santagati A. , Santagati M.
Published: May 2005

The 70 eV electron impact mass spectra of some 1,3,4‐thiadiazolo[3,2‐a]pyrimidin‐7‐one and isomeric‐5‐one derivatives are discussed with the aid of defocused metastable spectra and exact mass measurements. The compounds are shown to be very stable to electron impact and ring contraction reactions are in most cases the characterstic fragmentations. Most importantly, the 7‐one derivatives fragment by a retro‐Diels–Alder process which does not occur in the 5‐one isomers. This provides a diagnostic tool for differentiation between the isomers and for the unequivocal assignment of the structure.
Electron impact mass spectrometry of some benzodioxole derivatives of pharmacological interest, their synthons and synthetic intermediates
Authors: Podda Gianni , Maccioni Antonio , Fadda Anna Maria , Daolio Sergio , Pelli Beatrice , Traldi Pietro
Published: May 2005

The mass spectrometric behaviour of two newly synthesized β‐blocking benzodioxole derivatives, their synthons and synthetic intermediates has been studied in detail with the aid of exact mass measurements, linked scans, collisionally activated decomposition mass analysed ion kinetic energy spectra and deuterium labelling experiments. A retrosynthetic process, leading to the original synthons, is described.
The potential energy surface for the [C2H2O]+˙ system: The ketene radical cation [CH2CO]+˙ and its isomers
Authors: Bouma Willem J. , Gill Peter M. W. , Radom Leo
Published: May 2005

Ab initio molecular orbital calculations with large, polarization basis sets and incorporating valence electron correlation have been employed to examine the [C2H2O]+˙ potential energy surface. Four [C2H2O]+˙ isomers have been identified as potentially stable, observable ions. These are the experimentally well‐known ketene radical cation, [CH2CO]+˙ (a), and the presently unknown ethynol radical cation, [CH2COH]+˙ (b), the oxirene radical cation magnified image (c) and an ion resembling a complex of CO with [CH2]+˙, magnified image (d). The calculated energies of b, c and d relative to a are 189, 257 and 259 kJ mol−1, respectively. Dissociation of ions a and d is found to occur without reverse activation energy.
Intramolecular cyano group transfer in some ylidenemalononitrile dimers
Authors: Mokrosz Maria J.
Published: May 2005

Molecular ion fragmentation accompanied by intramolecular cyano group rearrangement has been observed for ylidenemalononitrile dimers containing heteroaromatic or phenyl substituents.
Assigning structures to ions in the gas phase
Authors: Holmes John L.
Published: May 2005

The purpose of this short review is critically to assess the important experiments in gas phase ion chemistry whose correct interpretation can lead to the assigning of structures to organic positive ions. The methods fall into two main categories, (i) the measurement of ion enthalpies and transition state energies for their fragmentations and (ii) the detailed examination of the unimolecular and collision‐induced fragmentation behaviour of cations, anions and neutral species. It is argued that in general, none of the above methods alone can suffice for an ion structure determination, but that in combination these techniques provide a powerful tool by means of which ion structures may confidently be assigned.
Heat of formation for the propanoyl cation by photoionization mass spectrometry
Authors: Traeger John C.
Published: May 2005

The ionization energies and [C3H5O]+ appearance energies for a series of oxygenated organic compounds have been measured by dissociative photoionization mass spectrometry. The adiabatic ionization energy for cyclopentanol is observed to be 9.72 eV. A 298 K heat of formation of 591.2±2.3kJ mol−1, based on the stationary electron convention, is derived for the propanoyl cation in the gas phase. A heat of formation of –86±6 kJ mol−1 is obtained for methylketene, which leads to an absolute proton affinity of 853±8 kJ mol−1.
The mass spectra of benzofuroxans—an example of an ortho effect
Authors: Chafin Andrew P. , Erickson Eric D.
Published: May 2005

The fragmentation behavior of a series of nine benzofuroxans has been studied under electron impact conditions. It was found that benzofuroxans without a nitro group in the 4‐position fragment principally through loss of N2O2 (the furoxan ring), whereas those with a nitro group ortho to the furoxan ring exhibit predominant loss of NO from position 1 of the furoxan ring.
Chemical ionization mass spectra of chlorine‐substituted aryl‐propio‐ and ‐butyro‐nitriles: Occurrence of an unusual radical‐induced cyclization process
Authors: Madhusudanan K. P. , Seth M. , Bhaduri A. P.
Published: May 2005

The chemical ionization (CI) induced reactions in certain chlorine‐containing aryl‐substituted alkyl nitriles have been studied using different reagent gases including ND3 and CD4 and with the help of collisional activation spectra. A few fragmentations can be explained only on the basis of protonation of or electrophilic attachment to neutral products formed in the CI source. A detailed investigation of the unusual dehalogenation and dehydrohalogenation reactions occurring in some of these molecules has shown that radical‐induced cyclization processes give rise to these ions.
Chemical ionization mass spectrometric characteristics of morphine alkaloids
Authors: Liu Ray H. , Low I. A. , Smith Frederick P. , Piotrowski Edwin G. , Hsu An‐fei
Published: May 2005

The ion‐molecular reaction behavior of ten morphine alkaloids with several commonly used reagent gases are studied under chemical ionization mass spectrometry conditions. These studies emphasize the correlation of the structural characteristics of the 10 alkaloids with the following four mass spectrometric parameters: (i) mass shifts of the protonated ion as a result of replacing ammonia with deuterated ammonia as the reagent gas, (ii) relative tendencies of the adduct ion and the protonated ion to lose molecules of water, (iii) relative intensity ratio of the adduct ion and the protonated ion and (iv) tendency of a compound to undergo a reduction reaction.
Interference to linear superposability of collisionally activated decomposition spectra at high resolution
Authors: Bursey Maurice M. , Hass J. Ronald
Published: May 2005

A new factor causing the superposability of collisionally activated decomposition spectra of ions to fail has been established for isobaric ions. If the two isobaric ion beams are not transmitted in their entirety simultaneously to the collision cell, the resulting spectrum is not a linear combination of the two spectra of the individually transmitted complete ion beams. Apparently the energy content of collimated ions varies across the ion beam, so that transmission of different portions of the ion beam produces samples of ions with different energy contents.
An algorithm for estimating the enthalpies of formation of amine molecular ions and immonium fragment ions
Authors: Maccoll Allan
Published: May 2005

A method of estimating the enthalpies of formation of amino molecular ions, ΔH⊖ ([CnH2n+1NH2]+˙) and of immonium ions ΔH([CnH2n+1N]+) is reported. It is based on the fact that CH3 is isoelectronic with NH2, CH2 with NH and CH with N. Some calculated values of the enthalpies of formation of amine molecular ions and immonium ions are reported and estimates are made of the accuracy of such calculation.
Stereochemical effects in mass spectrometry. 3—Detection of chirality by chemical ionization mass spectrometry
Authors: Suming Hua , Yaozu Chen , Longfei Jiang , Shuman Xue
Published: May 2005

It was found that the chemical ionization mass spectra of the enantiomers of some α‐amino acids and α‐hydroxy acids could be definitely distinguished when a chiral compound, l‐amyl alcohol, was used as a component of the reagent gases. The relative abundances of some characteristic ions produced through ion‐molecule reactions in the gas phase were much higher in the D isomers than in the L isomers. The results were highly reproducible. This approach proved to be a convenient way for the detection of the chirality of these compounds by chemical ionization mass spectrometry.
Energy deposition in [Fe(CO)5]+˙ upon collision with a metal surface
Authors: DeKrey Michael J. , Kenttämaa Hilkka I. , Wysocki Vicki H. , Cooks R. G.
Published: May 2005

Collision of the title ion upon a stainless steel surface at near‐normal incidence leads to deposition of internal energy in a well‐defined narrow distribution. The energy deposited increases with laboratory collision energy and exceeds 7 eV (average) for 100 eV collisions. The translational‐to‐vibrational energy transfer efficiency is 15% (assuming an infinitely massive target) at 25 eV collision energy. Comparison is made with the internal energy distributions associated with gas‐phase collisional activation using both low and high ion kinetic energies. The narrowness of the distribution of internal energies, the easy access to ions excited to different extents, and the high internal energies accessible, make the ion/surface collision process superior to gas‐phase collisional activation for this system.
Gas‐phase protonation of unsaturated ethers: Experimental and theoretical study of 2,3‐and 2,5‐dihydrofuran and related compounds
Authors: Bouchoux Guy , Djazi Faycal , Hoppilliard Yannik , Houriet Raymond , Rolli Eric
Published: May 2005

The protonation of 2,3‐ and 2,5‐dihydrofuran is examined in gas‐phase equilibrium proton transfer reactions conducted in an ion cyclotron resonance spectrometer. The thermodynamically favoured site of protonation in the two compounds is seen to be different: whereas the first isomer forms a carbocation upon protonation, the second isomer protonates on the oxygen atom to form an oxonium ion. The results obtained with substituted derivatives and with linear analogues confirm these conclusions. Molecular orbital calculations on the various structures for protonated bases are performed at the 4–31G level with correction for configuration interaction effects and at the 4–31G* level. The latter basis set provides the best results owing to the introduction of d‐type orbitals on the oxygen atom. The calculation results substantiate the experimental observations and provide details on the molecular structure of the protonated species.
Charge separation reactions of doubly charged benzene ions
Authors: Richardson P. J. , Eland J. H. D. , Lablanquie P.
Published: May 2005

Photoion‐photoion coincidence spectra of benzene and benzene‐d6 photoionized by He(II) light and synchrotron radiation show the existence of six major and eight minor charge‐separation reactions of the [C6H6]2+ ion. Three main groups of ion pairs are related to [C3H3]+ + [C3H3]+, [C2H3]+ + [C4H3]+ and [CH3]+ + [C5H3]+, with appearance energies of 32.2 ± 0.5 eV, 31.3 ± 0.5 eV and 28.4 ± 0.3 eV. The kinetic energy release is the same for all pairs within a group, irrespective of hydrogen number, but differs from group to group. Results are interpreted in terms of fast, direct charge separation of [C6H6]2+, and subsequent hydrogen loss by the singly charged fragments.
Molecular weight adjustment to probability based matching of unknown mass spectra
Authors: Stauffer Douglas B. , McLafferty Fred W.
Published: May 2005

For an unknown mass spectrum of lower molecular weight, there should be relatively fewer compounds in the reference file giving similar mass spectra. Testing this with the Probability Based Matching (PBM) algorithm, for a specific degree of match a reference compound of low molecular weight has a higher probability of being correct. Modifying the predicted reliability values for such matches statistically improves the overall performance of PBM appreciably at high reliability values.
Rapid characterization of biomaterials by field ionization
Authors: Schulten H.‐R. , Halket J. M.
Published: May 2005

The direct application of field ionization to complex biomaterials is described. Volatiles are characterized by gas chromatography mass spectrometry. Complex involatile materials are investigated by thermal degradation in high vacuum. The methodology and typical analytical features of pyrolysis of biopolymers and soft ionization of their pyrolysates in the high electric field are described. The combination of direct, in‐source pyrolysis mass spectrometry and pyrolysis gas chromatography mass spectrometry is used in two steps. Firstly, for fast profiling of the complex materials and, secondly, for identification of significant products of the controlled thermal degradation process. In particular, temperature programmed/time‐resolved pyrolysis field ionization mass spectrometry has been shown to be an efficient analytical tool as demonstrated for typical examples such as chitin, cellulose, hemicellulose, lignin, wood, peat and coal. Recent results on foodstuffs such as coffee, chocolate, tea and biscuits illustrate the potential of the combined methods for routine work.
Electron impact ionization of unstable enols: H2CCHOH, H2CC(OH)CH3 and H2CC(OH)C2H5
Authors: Iraqi Muhammad , Pri‐Bar Ilan , Lifshitz Chava
Published: May 2005

Ethenol, 2‐hydroxypropene and 2‐hydroxybutene‐1 were prepared by low‐pressure pyrolysis of cyclobutanol, 1‐methylcyclobutanol and 1‐ethylcyclobutanol, respectively. Mass spectra, ionization energies, appearance energies of metastable ions and kinetic energy releases were determined on a reverse Nier‐Johnson double‐focusing mass spectrometer. Mercury and CH3 radicals from the pyrolysis of dimethylmercury were employed for calibration of the energy scale. The ionization energy of 2‐hydroxybutene‐1 is 8.55 ± 0.1 eV and the appearance energies of [C2H5CO]+ and [CH3CO]+ from that molecule are 10.25 ± 0.1 and 10.40 ± 0.1 eV, respectively. Changes observed in metastable peak shapes for certain fragmentation reactions upon pyrolysis are discussed.
Study of ion structures produced by the reaction of 2‐propyl cations with water and methanol; covalently bound v. Hydrogen‐bridged adducts
Authors: Terlouw Johan K. , Weiske Thomas , Schwarz Helmut , Holmes John L.
Published: May 2005

In contrast to an earlier report,1 the collisonally induced dissociation of protonated 2‐propanol and t‐butyl alcohol yields spectra that are indistinguishable from those of the corresponding [C3H7/H2O]+ and [C4H9/H2O]+ ions generated by the (formal) gas phase addition reactions in a high pressure ion source of [s‐C3H7]+ and [t‐C4H9]+ ions with the n‐donor H2O. Similarly, [s‐C3H7/CH3OH]+ ions generated by both gas phase protonation of n‐ and s‐propyl methyl ethers and addition reactions of [C3H7]+ to CH3OH display mode‐of‐generation‐independent collisionally induced dissociation characteristics. However, analysis of the unimolecular dissociation (loss of propene) of the [C3H7/CH3OH]+ system, including a number of its deuterium, 13C‐ and 18O‐labelled isotopomers, supports the idea that prior to unimolecular dissociation, covalently bound [C3H7‐ O(H)CH3]+ ions intercovert with hydrogen‐bridged adduct ions, analogous to the behaviour of the distonic ethene‐, propene‐ and ketene‐H2O radical cations.
Neutralization‐reionization mass spectrometry (NRMS). Structural information from vertical neutralization and reionization efficiencies
Authors: Wesdemiotis Chrysostomos , Feng Rong , Williams Evan R. , McLafferty Fred W.
Published: May 2005

The neutralization‐reionization mass spectra of alkane radical ions indicate significant differences between the structures and geometries of alkane molecules and their molecular ions, confirming recent ab initio predictions. Ionic isomers that are indistinguishable by collisionally‐activated dissociation because of easy interconversion can be characterized by neutralization‐reionization if the corresponding neutrals show different reactivities, as is demonstrated for the [C2H5]+/C2H5˙ system and for [C2H4O2]+˙ isomers. For identification of mixtures of more than one neutral species, the relative efficiency for reionizing each neutral must be determined; e.g. the O2 reionization efficiency of ˙CH2OH radicals is ∼4 times greater than that of CH3O˙. This information and reference reionization spectra of CH3O˙ and ˙CH2OH show that metastable or collisionally activated methyl acetate cations lose CH3O˙, not ˙CH2OH as previously reported; the newly‐formed CH3O˙ undergoes partial (∼20%) isomerization to ˙CH2OH in the ∼10−6s before reionization. Similar results are obtained for [B(OCH3)3]+˙.
Mass spectral behavior of n‐alkynes
Authors: Mercer Roger S. , Harrison Ale X. G.
Published: May 2005

The 70 e V‐electron impact mass spectra of the C7–C10 n‐alkynes have been determined as well as the metastable ion spectra of the molecular ions and the [CS2]+ and [N2O]+ charge exchange mass spectra of the C7‐C9 n‐alkynes. The metastable ion mass spectra provide only a limited opportunity to distinguish between isomers; however, the 70‐eV EI mass spectra of isomeric compounds permit a ready distinction between isomers. The [CS2]+ charge exchange mass spectra of isomeric compounds also show substantial differences. The [N2O]+ charge exchange mass spectra do not show the enhancement of β‐fission fragments observed in field ionization experiments, despite representing ions of similar internal energy, and it is concluded that field dissociation is responsible for the β‐fission fragments in the field ionization experiments.
Tandem mass spectrometry of organophosphate and carbamate pesticides
Authors: Hummel Susan V. , Yost Richard A.
Published: May 2005

We present tandem quadrupole mass spectrometric data for 26 organophosphate and 16 carbamate pesticides. These data are of use in developing methods for screening samples for specific compounds (by selected reaction monitoring) or specific classes of compounds (by parent scans and neutral loss scans). Optimization of tandem mass spectrometry conditions for maximum sensitivity is also described.
Structures and relative energies of gas‐phase [C2H7N]+˙ radical cations
Authors: Yates Brian F. , Radom Leo
Published: May 2005

Ab initio molecular orbital calculations with split‐valence plus polarization basis sets and incorporating electron correlation and zero‐point energy corrections have been used to examine possible equilibrium structures on the [C2H7N]+˙ surface. In addition to the radical cations of ethylamine and dimethylamine, three other isomers were found which have comparable energy, but which have no stable neutral counterparts. These are \documentclass{article}\pagestyle{empty}\begin{document}$ \mathop {\rm C}\limits^{\rm .} {\rm H}_{\rm 2} {\rm CH}_{\rm 2} \mathop {\rm N}\limits^{\rm + } {\rm H}_{\rm 3} $\end{document}, \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm CH}_{\rm 3} \mathop {\rm C}\limits^{\rm .} {\rm H}\mathop {\rm N}\limits^{\rm + } {\rm H}_{\rm 3} $\end{document}and\documentclass{article}\pagestyle{empty}\begin{document}$ {\rm CH}_{\rm 3} \mathop {\rm N}\limits^{\rm + } {\rm H}_{\rm 2} \mathop {\rm C}\limits^. {\rm H}_{\rm 2} {\rm }, $\end{document} with calculated energies relative to the ethylamine radical cation of −33, −28 and 4 kJ mol−1, respectively. Substantial barriers for rearrangement among the various isomers and significant binding energies with respect to possible fragmentation products are found. The predictions for \documentclass{article}\pagestyle{empty}\begin{document}$ \mathop {\rm C}\limits^. {\rm H}_{\rm 2} {\rm CH}_{\rm 2} \mathop {\rm N}\limits^ + {\rm H}_{\rm 3} $\end{document} and \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm CH}_{\rm 3} \mathop {\rm C}\limits^{\rm .} {\rm H}\mathop {\rm N}\limits^{\rm + } {\rm H}_{\rm 3}$\end{document} are consistent with their recent observation in the gas phase. The remaining isomer, \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm CH}_{\rm 3} \mathop {\rm N}\limits^{\rm + } {\rm H}_{\rm 2} \mathop {\rm C}\limits^{\rm .} {\rm H}_{\rm 2} {\rm },$\end{document}is also predicted to be experimentally observable.
Fragmentations of protonated acetophenones via intermediate ion–molecule complexes
Authors: Filges U. , Grützmacher Hans‐Fr.
Published: May 2005

Protonated acetophenones, substituted with a methoxymethyl group in the para and meta positions, have been generated by electron impact induced fragmentation of the correspondingly substituted 2‐phenylpropan‐2‐ols. The metastable ions, formed in the second field‐free region of a VG ZAb 2F mass spectrometer, react unimolecularly by elimination of CH3OH, formation of CH3CO+ and magnified image ions, loss of CH3COOCH3, and loss of CH2O. The mechanisms of these fragmentations have been elucidated with the aid of deuterated analogues of the protonated acetophenones. It is shown that these reactions are initiated by an endothermic transfer of the proton at the carbonyl group of the protonated acetophenones to the benzene ring. A further migration of the proton to the ether O atom of the methoxymethyl side‐chain leads eventually to the elimination of CH3OH. Protolytic bond cleavages of either side‐chain gives rise to the CH3CO+ and magnified image ions. At low internal energies both these ions may be trapped by the aromatic neutral fragment in ion‐molecule complexes. Reactions within these complexes result in the energetically favourable losses of CH3COOCH3 and CH2O, respectively. With respect to these reactions, the protonated acetophenones behave analogously to the correspondingly substituted and protonated benzaldehydes.
A mass spectrometric study of the dimethyl ester trimethylsilyl enol ether derivatives of some 3‐oxodicarboxylic acids
Authors: Svendsen John S. , Whist Jon E. , Sydnest Leiv K.
Published: May 2005

The fragmentation pathways for the dimethyl ester trimethylsilyl enol ether derivatives of some 3‐oxodicarboxylic acids have been found by using B/E and B2/E linked scans, collisional activated decomposition and isotope substitution techniques. The trimethylsilyloxy group strongly directs the decomposition processes, and induces a fragmentation pattern that intimately reflects the structure of the compounds.
The mass spectrometric behaviour of benzohydroxaraic and benzothiohydroxamic acids under electron impact
Authors: Florěncio M. H. , Heerma W. , Santos M. A. , Tavares M. R. , Lobo A. M. , Prabhakar S.
Published: May 2005

Primary fragmentation reactions in benzohydroxamic and benzothiohydroxamic acids have been studied and compared with those in benzamides and benzothioamides. Mass‐analysed ion kinetic energy spectra, collisional activation spectra and spectral data from labelled compounds were used to elucidate fragment ion structures and reaction mechanisms. The mass spectra are shown to be dependent on ion source temperature. Losses of O and H2O are proved to be thermal in origin. The formation of an S… HO bond, which is analogous to an intramolecular hydrogen bond in solution chemistry, directs many fragmentation pathways. This seems to be the major factor determining the differences between the mass spectra of benzothiohydroxamic acids and those of the corresponding carbonyl compounds.
Charge exchange and charge separation processes of [C3Hn]2+ and [C3Dn]2+ (n = 1–6) dications
Authors: March Raymond E.
Published: May 2005

The charge exchange and charge separation processes of a series of [C3Hn]2+ and [C3Dn]2+ (n = 1–6) dications have been investigated experimentally in a mass spectrometer of reversed geometry. The relative reaction cross‐sections for charge exchange with nitrogen exhibited a 20‐fold variation which has implications for the interpretation of 2E spectra with respect to dication relative intensities. Charge separation resulting in deprotonation was observed for all [C3Dn]2+ species investigated, while de‐deuteronation was observed for [C3Dn]2+ (n = 1–4) only. Intercharge separations calculated from the observed ion kinetic energies released upon charge separation suggest linear structures for [C3Dn]2+ and [C3Dn]2+ (n = 1–2) and cyclic structures for [C3Dn]2+ (n = 3–6) and [C3Dn]2+ (n = 3–4).
Ion‐neutral complex‐mediated hydrogen exchange in ionized n‐butanol: A mechanism for ‘non‐specific’ hydrogen migrations
Authors: McAdoo David J. , Hudson Charles E.
Published: May 2005

Water elimination from ionized n‐butanol reflects near randomization of all hydrogens in ions decomposing after ∼10−5s. This probably takes place in ion‐neutral complexes by formation of a cyclobutane ion–H2O complex and/or rearrangement within [C4H8]+˙ in open‐chain [C4H8+˙H2O] complexes, in either case accompanied by hydrogen exchange between water and open‐chain hydrocarbon moieties. Extensive hydrogen rearrangements in which restraints on conventional transition‐state ring size have little apparent influence may generally be ion–neutral complex‐mediated processes.
Mechanism of reduction of double bond under chemical ionization conditions
Authors: Madhusudanan K. P. , Murthy V. Sreenivas , Fraisse D.
Published: May 2005

The mechanism of double bond reduction occurring in certain conjugated ketones, nitriles, acids and esters under chemical ionization conditions has been studied. The results indicate that the hydrogen radicals present in the chemically ionized plasma are responsible for the reduction of the double bond. This is further supported by experiments with radical traps.
Negative chemical ionization mass spectrometry of phenols, and their determination in acidic fractions of coal‐derived liquids
Authors: Strachan Michael G. , Anderson Geoffrey B. , Porter Quentin N. , Johns R. B.
Published: May 2005

The use of Freon–113 as a reagent gas in the negative chemical ionization mass spectra of phenolic compounds is reported. The dominant mode of ionization is by chloride attachment producing [M + Cl]− ions. The application of this technique to the highly phenolic acid fractions from coal‐derived liquids gives spectra containing essentially only [M + Cl]− peaks. This allows relative molecular mass profiles to be obtained. The resultant complex spectra are simplified by dividing them into their homologous series components. Since this is a low‐resolution technique, absolute component identification cannot be made; but in conjunction with other analytical methods, tentative identification of series of molecules is possible. Thus, the alkyl‐substituent ranges of the different homologous series can be assessed. Comparisons between coal‐derived liquids produced under different reaction conditions are made, and composition differences detected.
Electron impact mass spectra of some anthracene, anthrafuran and nitroanthrafuran derivatives. A tandem mass spectrometric collisional activation dissociation study
Authors: Sellier Nicole , Cazaussus Annie , Bilger Christine , Demerseman Pierre
Published: May 2005

The 70‐eV electron impact mass spectra of a series of thirty anthracene, seven anthra[2,1‐b]furan and seven 2‐nitroanthra[2,1‐b]furan derivatives are described and discussed. A collisional activation dissociation study of 1‐formyl‐2,6‐dimethoxy‐9‐methyianthracene, 1‐formyl‐2,6‐dimethoxy‐10‐methylanthracene, and 2‐carboxy‐11‐methylanthra[2,1‐b]furan has been carried out using tandem mass spectrometry in order to substantiate the fragmentation schemes.
Mechanism of the [C7H7]+ ion formation in the electron impact induced fragmentation of 3‐dimethylamino‐1‐phenylpropanone (Mannich's base)
Authors: Srzić D.
Published: May 2005

The genesis of the [C7H7]+ ion in the mass spectrum of 3‐dimethylamino‐1‐phenylpropanone (Mannich's base) hydrochloride has been studied by 13C and deuterium labelling and by application of metastable transitions. It has been shown that this ion is formed from [M − OH]+, involving non‐adjacent carbon atoms.
Mass spectral fragmentation pathways in reduction metabolites of 2,4‐dinitrotoluene and 2,4,6‐trinitrotoluene. A tandem mass spectrometric collision induced dissociation study
Authors: Yinon Jehuda
Published: May 2005

A collision induced dissociation study of a series of reduction metabolites of 2,4‐dinitrotoluene and 2,4,6‐trinitrotoluene was carried out using a tandem BB mass spectrometer. Fragmentation pathways of the metabolites were determined in the electron impact mode. It was found that the dominant fragmentation pathway is loss of OH˙ due to an ortho effect. Other fragmentation routes include loss of NO2˙ and loss of CH2N˙.
Collisionally activated decomposition of poly(ethylene glycol)s: An investigation of high‐mass ion abundances in the collisional activation technique with large molecules
Authors: Kiplinger Jeffrey P. , Bursey Maurice M.
Published: May 2005

The utility of the collisional activation technique in structure determination of ions is limited as parent ion mass increases. Optimum collisionally activated dissociation yield is often obtained at parent masses of 1000–2000 u, after which daughter ion yield decreases. The apparent decrease in the efficiency of the collisional activation process has been thought of as a degree‐of‐freedom effect: as new rotational‐vibrational modes are added to the parent ion, its lifetime with respect to dissociation increases. We have investigated this effect using an easily characterized system of several poly(ethylene glycol) homologs from the 15‐mer to the 35‐mer. Observed trends in the collisional activation spectra as parent mass increases support the postulated ‘degree‐of‐freedom’ effect in general. The loss of C2H4O from the [M − H]− parents, a fragmentation which has a high activation barrier, however, actually becomes more favored as the parent ion becomes larger. This effect is explained in terms of statistical rate theory.
Secondary ion emission from glycerol under continuous and pulsed primary ion current
Authors: Todd Peter J.
Published: May 2005

Secondary ion intensity from glycerol is measured as a function of 5 keV primary ion current density and is found to be linear over the range 0.1–1 μA cm−2. The possibility that protonated glycerol, or some other condensed‐phase precursor to secondary protonated glycerol, exists in solution and enhances secondary ion emission from glycerol is investigated. Kinetics for formation of such precursors by the primary ion beam are described and evaluated by pulsed primary ion beam experiments. Depletion rates are calculated assuming diffusion from the surface as the major loss mechanism Results of this analysis indicate that the mechanism for secondary emission of protonated glycerol does not involve formation of precursors, e.g. solution‐phase protonated glycerol, directly or indirectly by the primary ion beam.
The gas‐phase amino–claisen rearrangement of protonated N‐allylaniline
Authors: Kingston Eric E. , Beynon John H. , Flammang Robert , Maquestiau André
Published: May 2005

Metastable molecular protonated ions of N‐allylaniline dissociate with significant losses of ethene and ammonia in the flight path of a mass spectrometer. The structures of the daughter ions formed on the loss of ethene have been elucidated using collision‐induced dissociation and it is postulated that two isomeric structures are formed, one corresponding to molecular protonated ions which have undergone an amino–Claisen rearrangement. The relative proportion of this rearranged species is dependent on the exothermicity of the proton‐transfer reaction between the sample molecule and the chemical ionization reagent gas ion. It is proposed that the two isomeric parent species differ in the site of protonation.
Formation of thioacylium ions in the gas phase
Authors: Abd. Rahman Noorsaadah , Fisher Cindy L. , Caserio Marjorie C.
Published: May 2005

A study of the ion chemistry of benzenethioic acid using ion cyclotron resonance techniques shows that a long‐lived ion of composition C7H5S+ is formed from the reaction of the neutral acid with primary fragment ions, m/z 77 (phenyl) and m/z 105 (benzoyl). The product is assigned the thiobenzoyl structure on the basis df its mode of formation from benzoyl cations and tbe neutral acid. Other reactant ions (acetylium and thioacetylium) derived from mixtures of benzenethioic acid with ethanethioic acid or acetate esters similarly lead to thiobenzoyl ions as the major product The significance of these results as support for the thioacetylium structure of C2H3S+ ions from ethanethioic acid is discussed.
Do the aminopyridine molecular ions display aniline‐ or pyridine‐type behaviour?
Authors: Hop C. E. C. A. , Dakubu M. , Holmes J. L.
Published: May 2005

By means of collisionally induced dissociative ionization mass spectrometry it was shown that the three isomeric aminopyridine molecular ions display ion chemistry similar to aniline molecular ions; i.e. metastable HNC loss, rather than losing the more stable neutral species HCN, behaviour typical of ionized pyridine. The molecular ions do not isomerize to a common intermediate prior to fragmentation and can readily be distinguished from their collisional activation and charge‐stripping mass spectra.
Gas‐phase electrophilic addition reactions of chlorinated alkyl ions
Authors: Burinsky David J. , Campana Joseph E.
Published: May 2005

Chemical ionization was used to study gas‐phase electrophilic addition reactions of chloromethyl ions ([CHxCl3‐x]+, x = 0, 1, 2) with a number of substituted benzenes (C6H5Y, Y = NH2, OH, CHO, CN, NO2). Mass‐analyzed ion kinetic energy spectrometry was used to characterize the reaction products with respect to the site of electrophilic addition (ring v. substituent). In some cases, examination of secondary reaction products (ion–molecule adduct which has undergone an elimination reaction in the ion source) aided in establishing the original site of electrophilic addition. Aniline, benzonitrile and nitrobenzene exhibited preferential substituent interaction, while phenol and benzaldehyde gave a mixture of ring and substituent reaction products. These gas‐phase results differ considerably from solution‐phase Friedel–Crafts alkylation; however, they are consistent with the notion of preferential σ‐bond formation at polarizable centers of negative charge.
A comparative study on the behaviour of 1,3‐diheterocyclopentanes (X = O, O; S, S; O, S) under electron impact. The formation of thioacetyl and thiiranyl cations
Authors: Pihlaja Kalevi , Kuosmanen Pentti , Vainiotalo Pirjo
Published: May 2005

The electron‐impact‐induced mass spectra of 1,3‐dioxolane (la), 1,3‐dithiolane (2a) and 1,3‐oxatbiolane (3a) and their 2‐methyl (1b–3b) and 2,2‐dimethyl [(CH3)2: 1c–3c or (CD3)2: 1d–3d] derivatives have been studied in detail to gain further insight into their ion structures and competing reaction pathways with low‐resolution, high‐resolution, metastable and collision‐induced dissociation (CID) techniques. For compounds 1a–1d the most significant reaction is loss of H˙ and CH3˙ by α‐cleavage and a subsequent formation of CHO+ and C2H3O+ ions. The [M  H]+ ions from 1a and 1b give a C2H3O+ ion which does not have the acyl cation structure as shown by their CID spectra. In compounds 3a–3d the sulphur‐containing ions predominate, the C2H3O+ now having the acyl cation structure. 1,3‐Dithiolanes (2a–2d) exhibit the most complicated fragmentation patterns. Furthermore the [M  H]+ ion from 2a and [M  CH3]+ ion from 2b have different structures as well as the [M − H]+ ion from 2b and [M  CH3]+ ion from 2c, as shown by their CID spectra. This can be utilized to explain why 3a–3c and 2a give principally a thiiranyl cation, whereas 2b gives a mixture of this and the thioacyl cation and 2c practically only the open‐chain thioacetyl cation.
Gas‐phase reactions of electrons, halide ions and radicals with (meso‐tetraphenylporphinato)metal(II) complexes under negative ion chemical ionization conditions
Authors: Dillow G. W. , Gregor I. K.
Published: May 2005

The negative ion chemical ionization mass spectra of a series of (meso‐tetraphenylporphinato)metal(II) (metal = Mg, Co, Ni, Cu, Zn) complexes obtained with the electron‐energy‐moderating/reagent gases argon, NF3, CF2Cl2 and CF3Br are presented. Formation of the negative ions identified in the mass spectra is accounted for in terms of the chemistry which occurs in the gaseous plasmas. In argon plasmas, the metal complexes undergo resonance electron capture with comparable facility to produce stable molecular ions. In the NF3, CF2Cl2 and CF3Br plasmas, ionization occurs as a result of ion–molecule reactions as well as resonance electron capture, and is quite selective. Only fluoride ions react with each of the metal complexes, producing metal‐containing ions by nucleophilic addition and proton abstraction as well as by inducing ring closure. The less reactive chloride and bromide ions react readily by nucleophilic addition only with the magnesium and zinc complexes. Negative ions are also produced in the plasmas by radical‐molecule reactions followed by ionization of the neutral products of these encounters.
Mass spectroscopic studies of riboflavin and isotopically labelled lumiflavins
Authors: Holzmann Gerhard , Bock Michael , Elsner Martin , Kurreck Harry , Müler Franz
Published: May 2005

Under electron impact conditions 3‐methylriboflavin is attacked at the ribityl side chain to generate 3‐methyl‐lumiflavin. This is verified by analysis of metastable fragmentations and comparison with model ions. Formation of 1,3‐dimethyl‐lumkhrome through migration of the methyl group from N(10) to position N(1) is positively excluded. A general fragmentation scheme for ionized 3‐methyl‐lumiflavin is developed based on exact mass measurements using various2H,13C and15N isotopically labelled derivatives. The predominating initial loss of CH3NCO exclusively involves the 3‐ and 4‐positions, for which an asynchronous mechanism is discussed.
Low‐energy, low‐temperature mass spectra. 10—urethanes
Authors: Bowen Richard D. , Maccoll Allan
Published: May 2005

The 12.1 eV, 75°C electron impact mass spectra of 24 urethanes, RNHCO2C2H5 [R  H, C2H2n +1 (n = 1‐8), CH2CHCH2, Ph, PhCH2 and PhCH2CH2], and seven symmetrically disubstituted urethanes R2NCO2C2H5 (R  Cn H2n + 1 (n = 1−4)) are reported and discussed. All 31 spectra show appreciable molecular ion peaks. For n −Cn H2n +1 NHCO2C2H5, M+ ˙ usually is the most abundant ion in the spectrum. A peak at m/z 102 of comparable intensity also is present; this corresponds to formal cleavage of the bond connecting the α‐ and β‐carbon atoms in the N‐alkyl group, though it is unlikely that the daughter ion has the structure [CH2NHCO2C2H5]+. In the RNHCO2C2H5 series, branching at the α‐carbon atom enhances the relative abundance of the ion arising by notional α‐cleavage at the expense of that of M+ ˙. Formal cleavage of the bond between β‐ and γ‐carbon atoms occurs to some extent for [RNHCO2C2H5]+˙ ions; this reaction provides information on the degree of branching at the β‐carbon, especially if metastable molecular ions are considered. The higher n‐CnH2n +1NHCO2C2H5 (n = 5−8) urethanes exhibit two other significant ions in their mass spectra. First, there is a peak at [M  C2H5]+. Secondly, a peak is present at m/z 90; the most plausible structure for this ion is [H2N(HO)COC2H5]+, arising by double hydrogen transfer from the alkyl group and expulsion of a [CnH2n −1]˙ radical. Ions originating from secondary decomposition of the primary ionic species are generally of only very low abundance in these spectra.
Relation between alkali ion affinity and ionic radius ratio by means of fast atom bombardment tandem mass spectrometry
Authors: Isa Kimio , Takeuchi Yasutaka
Published: May 2005

Cationization of organic molecules has been studied using fast atom bombardment mass spectrometry and tandem mass spectrometric methods. The order of the A+ affinity to G (G − H + A) and AX was determined by this tandem mass spectrometric approach, where G, A and X represent glycerol, alkali metal element and halogen element, respectively. The affinity orders of most alkali halides are divided into three classes. By analogy with the ionic radius ratio rule in solid ionic crystals, this particular parameter, ionic radius ratio, was introduced to analyse the experimental results. This classification is thought to be caused by the ionic radius ratio (X−/A+). These ratios of the I, II and III classes exist between 0.657 and 1.026, 1.096 and 1.776, and 1.856 and 2.289, respectively. The ionic radius ratio plays an important role for determination of the order of alkali ion affinity.
On the mechanism of secondary ion formation from poly(methylmethacrylate) under static secondary ion mass spectrometry conditions
Authors: Lub J. , Benninghoven A.
Published: May 2005

The negative ion spectrum of a relatively thick layer (± 0. 5 μm) of poly(methylmethacrylate) (PMMA) with M̄w = 1890 and its positive ion spectrum of a very thin layer (± 1. 0 nm) on silver measured with a time of flight secondary ion mass spectrometer are presented. From the negative ion spectrum it is concluded that formation of enolate anions from PMMA under static secondary ion mass spectrometric conditions is an important ion formation process. From fragmentation products of the polymer, detected as silver cationized species in the positive ion spectrum, more evidence was found of a fragmentation mechanism for PMMA under static secondary ion mass spectrometric conditions recently proposed in the literature. From the relation between the information obtained from the two types of spectra an extension of this mechanism is obtained. This mechanism implies scission of the polymer chain by the primary ion bombardment with subsequent formation of enolate anions from the newly formed polymer chain‐ends.
Ortho effects in organic molecules on electron impact: 18—Novel hydrogen transfer from the methoxy group to acetylenic carbon in 2‐methoxyphenylacetylene and 2‐methoxydiphenylacetylenes
Authors: Ramana D. V. , Rama Krishna N. V. S.
Published: May 2005

The transfer of a hydrogen from the ortho methoxy group to the acetylenic carbon in 2‐methoxyphenylacetylene under electron impact conditions affords the rearranged molecular ion corresponding to 2H‐1‐benzopyran. Similar processes leading to cyclic products are also noticed in 2‐methoxydiphenylacetylenes. The ion structures and the mechanism of fragmentations are established through high‐resolution data, collision‐induced decomposition, mass‐analysed ion kinetic energy spectra, B/E linked scan spectra, D‐labelling and chemical substitution.