bluuebunny/crossref_metadata_2025_split huggingface dataset:
Plant‐polyphenols and related compounds. A mass‐spectrometric study of the trimethylsilyl derivatives of hydroxy‐ and/or methoxy‐substituted cinnamic acids and of their methyl esters
Authors: Horman I. , Viani R. 
Published: May 2005

AbstractThe low resolution 70 eV mass spectra of the TMS (Trimethylsilyl) derivatives of eight naturally occurring hydroxy‐ and/or methoxycinnamic acids are presented in detail. The TMS derivatives studied are I, of o‐coumaric acid; II, of m‐coumaric acid; III, of p‐coumaric acid; IV, of isoferulic acid; V, of ferulic acid; VI, of 3,4‐dimethoxycinnamic acid; VII, of sinapic acid; VIII, of caffeic acid; Ia to Va, VIIa, of the corresponding methyl esters; and VIa, methyl 3,4‐dimethoxycinnamate.The derivatives studied show a high degree of stability under conditions of electron‐impact. The major fragmentation processes for the free acid TMS derivatives begin with methyl radical loss from either the ester or ring TMS group. The spectra of the methyl ester TMS derivatives have enabled the site of initial methyl loss to be determined. Accurate mass measurements and analysis of the second field‐free region metastable peaks provide support for suggested fragmentation schemes. The spectra are sufficiently different to permit identification except between compounds IV and V (and IVa and Va) where the major fragmentation process involves a common ion, thought to be the silicon analogue of an acetonide.
The effect of deuterium labeling on the width of a ‘metastable peak’
Authors: Beynon J. H. , Caprioli R. M. , Ast T. 
Published: May 2005

AbstractStudies have been made of the energy release during the decomposition of metastable ions in the mass spectra of pyrazine, pyrazine‐d4, pyrimidine, pyrimidine‐d4, pyridazine and symmtriazine. In all the compounds except pyridazine very small amounts of energy have been measured in some processes. The recorded energy release of 187 μeV for a transition of the symmtriazine molecular ion is the smallest energy release yet recorded. In the case of pyrazine and pyrimidine the energy release in one transition was found to be smaller than in the corresponding transition in the ‐d4 analogues.
‘Doubly charged ion’ mass spectra of some simple aromatic compounds
Authors: Beynon J. H. , Mathias A. , Williams A. E. 
Published: May 2005

AbstractBenzene, toluene, phenol, diphenyl ether and the three isomeric dihydroxy‐benzenes have been examined using an MS‐9 mass spectrometer under conditions that allowed only ions having twice the normal amount of kinetic energy to be detected. These ions are, in fact, singly charged ions arising from charge exchange reactions of doubly charged ions of the same mass, occuring in the first field free region of the Spectrometer. It is argued that the spectra obtained yield essentially the distribution of doubly charged ions in the source region. These ‘doubly charged ion’ mass spectra are compared with the normal singly charged ion spectra of the compounds and the implications of the significant differences that are found, are discussed.
The electron impact‐induced fragmentation of 2‐arylthiazoles
Authors: Rix M. J. , Webster B. R. 
Published: May 2005

AbstractThe mass spectrometric fragmentation of 2‐aryl thiazoles centres, like that of simple thiazoles, around the cleavage of the 1,2 and 3,4 bonds of the thiazole ring. One characteristic species does arise from the fission of the 1,5 and 2,3 bonds, viz. a thiobenzoyl ion. The fragmentations of some substituents at the 4 and 5 positions of the thiazole ring, prior to ring cleavage, are also described.
Charge localization—I The ion kinetic energy spectra of ortho‐, meta‐ and para‐phenylenediamine
Authors: Caprioli R. M. , Beynon J. H. , Ast T. 
Published: May 2005

AbstractThe ion kinetic energy spectra of o‐,m‐and p‐phenylendiamine are presented. Decompositions of doubly‐charged ions are given for the three isomers. From the width of the peaks, the energy released is measured and the equivalent intercharge distance is calculated. The results are discussed in terms of possible structures of the various ions. Also, metastable transitions which could give rise to peaks corresponding to energies below that of the mainion beam are listed and the results discussed. Significant differences were observed among the energy spectra of the three isomers.
Nitrogen elimination in the mass spectra of diphenyl and triphenyl‐v‐triazoles
Authors: Compernolle F. , Dekeirel M. 
Published: May 2005

AbstractThe mass spectra of seven v‐triazoles (I to VII), having two or three phenyl substituents in 1, 4 and 5 positions, are described. Differences in the rate of nitrogen elimination from themolecular ions of I to III and IV to V are explained by the statement that this reaction requires a higher energy of activation for the transition state in IV to V than in I to III. At high electron voltages the relative intensities of fragment ions and metastable ions are very similar in the mass spectra of 1,4,5 triphenyl‐v‐triazole (I) and the ketenimine (VIII). Differences in the low electron voltage spectra of I and VIII, and energy measurements, however, show that probably an azirine ion IX is involved in the formation of the [M‐N2]+ ion from I. It is shown that production of the rearrangement ion m/e 165 (C13H9) isa high energy process.
Hydrogen exchange in a six‐membered ring transition state. Evidence for a stepwise McLafferty rearrangement
Authors: Briggs P. R. , Shannon T. W. , Vouros Paul 
Published: May 2005

AbstractMass spectra of 2‐methyl‐5‐chloro‐3‐N‐ethyl‐benzothiazolium iodide and labeled counter‐parts are discussed with particular emphasis on the loss of ethylene from the moiety produced by thermal elimination of HI from this salt. This process demonstrates the stepwise nature of a McLafferty rearrangement involving a hydrogen transfer to an olefinic carbon.
Field ionization mass spectrometry—III: Cardenolides
Authors: Brown Peter , Brüschweiler Fred , Pettit George R. , Reichstein T. 
Published: May 2005

AbstractThe electron impact (EI) and field ionization (FI) mass spectra of some representative underivatized cardenolides have been studied together for the first time, with the objective of assessing the structural and in particular the sequence information afforded by this promising analytical method. Two series of cardenolides have been examined, each consisting of a mono‐, di‐ and trisaccharide glycoside. The first was based on the aglycone digitoxigenin and comprised neriifolin, thevebioside and cerberoside; the second was based on the genin strophantidin and included cymarin, K‐strophantin‐β and K‐strophantoside. Other cardiac glycosides investigated and discussed include digitoxin and helveticoside. Important and structurally diagnostic fragmentations have been uncovered, especially in FI mode. In addition, the EI and FI spectra of individual components of the cardenolides have been recorded, e.g. the genins digitoxigenin and strophantidin, and the mono‐saccharides L‐thevetose, D‐cymarose and D‐glucose.
Interaction and rearrangement of trimethylsilyloxy functional groups. The structural significance of the m/e 147 ion in the mass spectra of trimethylsil steroidal ethers
Authors: Sloan Sharon , Harvey D. J. , Vouros Paul 
Published: May 2005

AbstractRequirements for trimethylsilyloxy group interaction and rearrangement are discussed. It is evident that formation of the m/e 147 ion is a function of the stereochemistry, steric hindrance and separation of the trimethylsilyloxy groups and reflects the stereochemistry of the steroid itself. It is postulated that ring cleavage is not necessarily a prerequisite for the formation of this ion. The occurrence of the m/e 147 ion can be structurally informative in trimethylsilyl derivatives of steroidal alcohols.
Benzopyrones—V Mass spectra of some ethyl 4‐oxochromen‐2‐carboxylates and related compounds
Authors: Barker G. , Ellis G. P. 
Published: May 2005

AbstractThe mass spectra of 23 chromone derivatives are recorded and interpreted. Most of these are ethyl 4‐oxochromen‐2‐carboxylate derivatives, which with two exceptions, show the molecular ion as the base peak. In the spectrum of the unsubstituted ester (XVIII), the other most important fragments are [M—C2H4], [M—OEt], [M—C2H4—CO], [M—CO2Et + 1] and the benzocyclopropenyl ion. 6‐Hydroxy‐2‐methylchromone and several of its derivatives undergo a retro‐Diels‐Alder reaction (R.D.A.) and also lose the carbonyl group. Ethyl 6‐amino‐4‐oxochroman‐2‐carboxylate (XXIII) shows an R.D.A. reaction as well as losing the CO2Et group. The mass spectrum of 4‐oxochromen‐2‐carboxylic acid has been studied.
Concerning the structure and fragmentation of [C3H7O]+ ions derived from alcohols
Authors: Tsang C. W. , Harrison A. G. 
Published: May 2005

AbstractThe formation of [CH2OH]+. by fragmentation of [C3H7O]+. ions in the electron‐impact mass spectra of 2‐methyl‐2‐propanol and 2‐propanol has been investigated using 13C labeling, deuterium labeling and metastable studies. The similar fragmentation reaction in the chemical ionization mass spectrum of acetone has been studied. It is concluded that the fragmentation reaction does not involve complete randomization of the carbon atoms and therefore does not proceed through formation of a hydroxylated cyclopropane intermediate. Alternative mechanisms are discussed.
Mass spectra of organometallic compounds—XIII: Metal carbonyl complexes of tris(dimethylamino)arsine
Authors: King R. B. , Korenowski T. F. 
Published: May 2005

AbstractThe mass spectra of the tris(dimethylamino)arsine metal carbonyl complexes [(CH3)2N]3‐AsM(CO)5 (M = Cr, Mo and W), trans‐[(CH3)2N]3AsCr(CO)4As[N(CH3)2]3 and [(CH3)2N]3‐AsFe(CO)4 were examined and compared with those of the corresponding tris(dimethylamino)‐phosphine complexes. The molecular ions in the mass spectra of the tris(dimethylamino)arsine complexes have a greater tendency to eliminate a (CH3)2N fragment than the molecular ions in the mass spectra of the corresponding tris(dimethylamino)phosphine complexes. The mass spectrum of the tungsten derivative [(CH3)2N]3AsW(CO)5 exhibits not only the usual series of ions [(CH3)2N]3‐AsW(CO)n+ and [(CH3)2N]2AsW(CO)n[+ but also the series of ions (CH3)2NAsW(CO)n]+ (n = 5, 4, 3, 2, 1 and 0) and even the nitrogen‐free ions [AsW(CO)n]+ (n = 2, 1 and 0). Metastable ion evidence was obtained for arsine (AsH3) elimination from the [(CH3)2N]2AsFeH+ ion in the mass spectrum of [(CH3)2N]3AsFe(CO)4.
The structure of the product ion of a ‘McLafferty’ rearrangement
Authors: Beynon J. G. , Caprioli R. M. , Shannon T. W. 
Published: May 2005

AbstractA series of alkylphenylketones has been examined. Whenever the alkyl chain is three or more carbon atoms long, the well‐known McLafferty rearrangement occurs with elimination of the elements of a neutral olefin. The further fragmentation of the ion formed in this rearrangement reaction has been studied using the technique of ion kinetic energy (IKE) spectroscopy. The measured release of kinetic energy has been used to show that the rearrangement ion has an enolic type structure.
Appearance potentials determined by the electron‐impact method as an analytical aid in the evaluation of conformational energies and clarification of ring conformation—I: Appearance potentials of the [MR]+· ions formed in the primary fragmentation of stereo‐isomeric 1,3‐dioxans. A direct route to conformational energies
Authors: Pihlaja Kalevi , Jalonen Jorma 
Published: May 2005

AbstractThe appearance potentials for the major primary fragmentation ions of three pairs of isomeric methyl‐1,3‐dioxans were measured. The correlation between the differences in these appearance potentials for each pair and the differences in the standard heats of formation for the corresponding isomer pairs is discussed.
The mass spectra of some corticosteroid boronates
Authors: Brooks C. J. W. , Middleditch B. S. , Harvey D. J. 
Published: May 2005

AbstractThe mass spectra of methyl, n‐butyl, t‐butyl, phenyl and cyclohexyl boronates of various classes of steroid are reported and discussed. Steroid types represented are 17α, 21‐dihydroxy‐20‐ketones, 17α, 20, 21‐triols, 17α, 20‐diols, 20, 21‐ketols. Each gives rise to characteristic fragmentation modes, although derivatives of the 20α‐ and 20β‐hydroxy compounds have similar spectra.
Substituent effects in the mass spectral fragmentation of aryl esters
Authors: Feil V. J. , Sugihara J. M. 
Published: May 2005

AbstractThe mass spectra of m‐ and p‐substituted phenyl acetates, phenyl propionates, phenyl chloroacetates and phenyl fluoroacetates have been determined. The fragmentation of aryl esters is affected by acyl substituents as well as by aryl substituents. Esters having acyl groups of low ionization potential show greater changes in fragmentation because of aryl substituents than those having acyl groups of high ionization potential. Each series has a fairly definite crossover point where fragmentation changes from predominant rearrangement to predominant cleavage.
Mass spectra of some dithiocarboxylic acid esters
Authors: Leon N. H. 
Published: May 2005

AbstractThe mass spectra of a variety of aliphatic esters of aromatic dithiocarboxylic acids are reported; their breakdown patterns are compared with those of the corresponding oxygen esters, O‐alkyl thioesters and S‐alkyl thioesters. Small quantities of O‐alkyl thioesters present in alkyl dithioesters can be detected by the appearance of the peak [ArCO]+.
Ionization and dissociation of cyclic ethers and thioethers by electron‐impact. A comparison between 1,3‐dioxolane, 1,3‐dithiolane and 1,3‐oxathiolane
Authors: Conde‐Caprace G. , Collin J. E. 
Published: May 2005

AbstractThe various modes of fragmentation of 1,3‐dithiolane and 1,3‐oxathiolane under electron‐impact have been discussed on the basis of the variation of their mass spectra with electron energy, the high resolution analysis and the AP's of the main ions. They are shown to be similar in both compounds, but considerably different from those of 1,3 dioxolane. From the AP of the [C2H5S]+ ion in 1,3‐dithiolane, a heat of formation of 63 kcal/mol for the free radical CHS is obtained.
A comparison of the unimolecular decomposition pathways of some C7 and C8 ions in the gas phase
Authors: Dale A. J. , Weringa W. D. , Williams Dudley H. 
Published: May 2005

Abstract[CnH2n−3]+ and [CnH2n−4]+·(n = 7, 8) ions have been generated in the mass spectrometer from CnH2n−3 Br (n = 7, 8) precursors and from two steroids. The relative abundances of competing ‘metastable transitionss’ indicate (partial) isomerization to a common structure (or mixture of structures) prior to decomposition in most examples of all four types of ions. In contrast, [C8H10O]+· and [C8H12O]+· ions, generated from different sources as molecular ions and by fragmentation of steroids, do not decompose through common‐intermediates.
High resolution mass spectrometry. Bufadienolides—II.
Authors: Brown Peter , Kamano Yoshiaki , Pettit George R. 
Published: May 2005

AbstractComplete low resolution mass spectra and high resolution data for selected important peaks are presented and discussed for a series of naturally occurring 14β, 15β‐epoxybufadienolides (toad poisons) and their derivatives. The compounds examined were resibufogenin, marinobufagin, cinobufagin, desacetylcinobufagin, cinobufotalin, desacetylcinobufotalin and resibufagin, and the derivatives were 11α‐hydroxyresibufogenin, 3β‐acetoxymarinobufagin, 3‐ketocinobufagin, 3β‐acetoxy‐16β‐desacetylcinobufagin, 3β‐acetoxy‐16‐ketocinobufagin, resibufaginol, 14α‐artebufogenin and 3β‐suberyloxyresibufogenin methyl ester. The relatively unsaturated 2‐pyrone group of C‐17β has been used as an integral label to distinguish (from elemental composition data) ions containing it from those arising in other parts of the molecule that do not, and the spectra are interpreted in terms of structural ‘ion types’.
Charge Localization: Doubly‐Charged Ion Reactions in Toluene
Authors: Ast T. , Beynon J. H. , Cooks R. G. 
Published: May 2005

AbstractThe kinetic energy released in the major charge‐separation reactions of [C7H8]++ [C7H7]++ and [C7H6]++ formed from toluene, and in the corresponding reactions of toluene‐α‐d3, toluene‐d8 and 2,3,4,5,6‐toluene‐d6 has been measured. Some fragmenting [C7]++ ions are linear; in certain cases they have cyclic structures while in others ‘coiling’ of a linear ion to allow hydrogen transfer in the transition state is suggested. From relative metastable ion abundance data it is apparent that nearly complete H/D randomization accompanies these slow reactions.
Ion cyclotron resonance spectrometry. A means of evaluating ‘kinetic shifts’
Authors: Gross Michael L. 
Published: May 2005

AbstractIon Cyclotron Resonance Spectrometry Is Proposed As The Method For Evaluating ‘Kinetic Shifts.’ The Proposal Is Tested By A Comparison Of The Appearance Potentials For Some Simple Cleavage Reactions With Those For Some Cleavage And Rearrangement Fragmentations In Benzene, Benzonitrile, Anisole, Aniline And Cubane.
Negative ion mass spectra of chlorine‐containing molecules
Authors: Ito Akihiko , Matsumoto Kozo , Takeuchi Tsugio 
Published: May 2005

AbstractThe negative ion mass spectra of chlorine‐containing molecules have been measured using a double focusing mass spectrometer with a photographic plate detector. The formulae of the negative ions not previously assigned using an electron multiplier detector have now been assigned.
Mass spectra of organoboron compounds—II: The mass spectra of triphenylboroxine and its precursor phenylboronic acid
Authors: Cragg R. H. , Todd J. F. J. , Weston A. F. 
Published: May 2005

AbstractThe mass spectrometric fragmentation pattern of phenylboronic acid has been determined and that of triphenylboroxine redetermined and extended, and the origin of some high abundance ions, previously unassigned, have been identified.
Aryl versus alkyl and vinyl migration in the mass spectra of sulphone derivatives
Authors: Soothill Rayner J. , Williams L. R. 
Published: May 2005

AbstractThe 2‐acetoxyethyl aryl sulphones were found to be unsuitable for a comparative study with the corresponding chlorides and alcohols as their predominant fragmentation involved cleavage of the aliphatic carbon‐sulphur bond with charge retention on the aliphatic part of the molecule The expected McLafferty rearrangement to yield an intermediate vinyl species was only a minor fragmentation path.Indirect evidence for alkyl migration in the molecular ion was found in the spectrum of 2‐acetoxyethyl 1‐paranitro phenyl sulphone. The spectra of the aryl vinyl sulphones revealed intense [Aryl SO]+ ions resulting from preferred migration of the vinyl group from sulphur to oxygen.
Mass spectrometry in structural and stereochemical problems—CCXIX: Identification of an unidirectional quadruple hydrogen transfer process in 7‐phenylhept‐3‐en‐2‐one o‐methyl oxime ether
Authors: Liedtke Raymond J. , Sheikh Younus M. , Duffield A. M. , Djerassi Carl 
Published: May 2005

AbstractExtensive deuterium labeling of 7‐phenylhept‐3‐en‐2‐one O‐methyl oxime ether has made possible the first documentation of an unidirectional quadruple hydrogen transfer process. Three other double hydrogen transfer processes are also described. Several of these multiple hydrogen transfer processes must utilize either a seven‐ or eight‐membered transition state.
Mass spectrometry of heterocyclic compounds—II: Electron‐impact induced fragmentation of 3,5‐diphenyl‐1,2,4‐oxadiazole
Authors: Selva A. , Zerilli L. F. , Cavalleri B. , Gallo G. G. 
Published: May 2005

AbstractThe electron‐impact induced fragmentation of 3,5‐diphenyl‐1,2,4‐oxadiazole has been investigated by labelling experiments, defocused metastable ion detections and high resolution mass measurements. The main fragmentation process suggests heterocyclic cleavage at the 1 to 5 and 3 to 4 bonds confirming our previous interpretation. The structure of the major fragment ion [C7H5NO]+· has been interpreted as being represented by the isomeric benzonitrile oxide and phenylisocyanate structures, the latter isomerising irreversibly from the former. The benzonitrile oxide structure is consistent with [C7H5NO]+· formation by cleavage of the 1 to 5 and 3 to 4 bonds.
Loss of HCN and H⋅ from the molecular ion of imidazole
Authors: Klebe K. J. , Van Houte J. J. , Van Thuijl J. 
Published: May 2005

AbstractThe behaviour of a number of deuterated imidazoles upon electron‐impact has been studied. Loss of H⋅ from the molecular ion occurs specifically at the 4(5)‐position. Loss of HCN is less specific, the order being 2 > 4(5) ≫ 1.
Specific rearrangements of 2,4‐dimethyl‐1‐pentene upon electron‐impact
Authors: Stefani Annibale 
Published: May 2005

AbstractA mass spectrometric investigation at 70 eV and at low voltage of specifically deuterated and undeuterated 2,4‐dimethyl‐1‐pentene is reported, in order to illustrate the specificity of the degradation reactions occurring under electron‐impact. A mechanism for the skeletal rearrangement of the molecular ion prior to fragmentation is proposed.
Energy and substituent effects on gaseous ionic decompositions: Electron and charge exchange ionization of benzophenones and benzils
Authors: Einolf Noel , Munson Burnaby 
Published: May 2005

AbstractThe correlation with substituent constants reported previously for [YØCO]+/[ØCO]+ ratios in the electron ionization mass spectra of substituted benzophenones and acetophenones has also been observed in the electron ionization spectra of substituted benzils. The [YØCO]+/[ØCO]+ ratio for the substituted benzils varied with energy of the ionizing electrons according to predictions from a simple kinetic and thermochemical analysis. [YØCO]+/[ØCO]+ ratios in the charge exchange spectra of benzophenones obtained with Xe, Kr, CO, N2 and Ar gave good correlations with sub‐stituent constants in agreement with the same analysis. Good correlations were also noted for [YØCO]+/[ØCO]+ ratios with substituent constants for [M]+ ions of the benzophenones of the same excess energy (5.5 eV). [YØCO]+/[ØCO]+ ratios for benzils obtained by charge exchange with [CO]+ also showed good correlations with substituent constant. It is suggested that [Ø]+ and [YØ]+ ions from the benzophenones may be formed primarily by one step decompositions of the molecular ions, but that the [Ø]+ and [YØ]+ ions from the benzils are formed primarily by decomposition of [ØCO]+ and [YØCO]+ ions.
The structure of the benzene molecular ion
Authors: Keough T. , Ast T. , Beynon J. H. , Cooks R. G. 
Published: May 2005

AbstractThe kinetic energy released by the [C6H6]+. ion generated (i) by direct ionization of benzene and (ii) by charge‐exchange of [C6H6]++ suggests that the reactive form of the benzene molecular ion has an acyclic structure.
The mass spectra of potential antidiabetics: 4‐Arylhydrazono‐3‐methyl isoxazol‐5‐ones and pyrazol‐5‐ones
Authors: Fenwick R. G. , Garg H. G. 
Published: May 2005

AbstractThe mass spectra of variously substituted 4‐arylhydrazono‐3‐methyl isoxazol‐5‐ones and pyrazol‐5‐ones have been examined, and the fragmentation pathways elucidated. The spectra of the former compounds differ from previously reported 4‐arylidene derivatives and this difference has been attributed to fragmentation involving the NHNmoiety. The investigation has shown up some interesting ‘ortho effects’ as well as the facile loss of HNCNH from N‐amidino derivatives of the pyrazol‐5‐ones.