bluuebunny/crossref_metadata_2025 huggingface dataset:
Mass spectrometry—III: Further studies of the unimolecular decomposition of acetophenone azine in the gas phase induced by electron‐impact
Authors: Scheppele Stuart E. , Grigsby Ronald D. , Whitaker Donald W. , Hinds Susan D. , Kinneberg Keith F. , Mitchum Ronald K.
Published: May 2005

Mass spectra of acetophenone azine‐d10 (II) and acetophenone azine‐d6 (III) were obtained to ascertain the validity of the proposed mass spectral fragmentation mechanisms proposed for acetophenone azine (I). Data from II and III reveal that the [M –1] ion in the spectrum of I is formed via loss of ring hydrogen. Within experimental uncertainty the major fragmentation reactions of the molecular ion of I, the [M –1] ion, and the [M –15] ion occur without loss of structural identity of the phenyl and methyl moieties. Ionization of I occurs with a high degree of structural integrity.
Reactions of aliphatic aldehydes under electron‐impact
Authors: Meyerson Seymour , Fenselau Catherine , Young J. L. , Landis W. R. , Selke Edward , Leitch L. C.
Published: May 2005

The mass spectra of hexanal, heptanal and nonanal variously labeled with deuterium confirm γ‐hydrogen migration and β cleavage as the mechanism leading to [C2H4O]+˙ and [M  C2H4O]+˙, although the data on the latter are complicated by contributions from other, related paths. In addition, they show that three other major primary decomposition products, [M  C2H4]+˙, [M  H2O]+˙ and [C3H5O]+, all arise in large part by processes involving γ‐hydrogen migration to the oxygen atom. The ethylene lost to yield the first of these products consists of the α and β methylene groups. The loss of ethylene most likely occurs by way of a cyclobutanol intermediate, which, via alternative reaction paths, may well contribute to the yields of the other two products as well. These findings further extend the range of parallelism between photochemical and electron‐impact‐induced reactions.
The mass spectra of N‐adamantoylpeptides
Authors: Lengyel István , Salomon Ramon A. , Biemann Klaus
Published: May 2005

The N‐adamantoyl derivatives of the esters of twenty‐one di‐peptides and eight tri‐peptides containing the amino acids glycine, alanine, valine, leucine, isoleucine, proline, phenylalanine, glutamic acid, lysine, histidine, serine, threonine, methionine, S‐benzylcysteine and tyrosine were prepared and their mass spectra determined. The spectra of all compounds were suitable for amino acid sequence determination. Mixtures containing N‐adamantoyl dipeptide and tripeptide methyl esters were separated by thin‐layer chromatography and the components identified by high resolution mass spectrometry. The mass spectrometric features of N‐adamantoyl peptide esters are discussed and compared with those of other N‐acyl peptide derivatives.
Mass spectra of selected beta‐carbolines [β‐9H‐pyrido(3,4‐b)indoles]
Authors: Coutts R. T. , Locock R. A. , Slywka G. W. A.
Published: May 2005

The mass spectra of fifteen β‐carbolines have been interpreted and proposed fragmentations have been substantiated by means of deuterium‐labeling and accurate mass determinations. Most decompositions were predictable. An interesting fragmentation was observed in the spectra of 1‐alkyl‐1,2,3,4‐tetrahydro‐β‐carbolines, which rearrange to expel an alkylamino (RNH) radical from the molecular ion.
Skeletal rearrangement in the mass spectra of tetrasilaadamantanes
Authors: Gohlke R. S. , Robinson R. J.
Published: May 2005

The loss of methyl group giving a peak of high intensity is observed in the mass spectra of 1,3,5,7‐tetrasilaadamantanes. This skeletal rearrangement must involve the simultaneous rupture of three bonds and concomitant hydrogen transfer. The spectra of the tetrasilaadamantanes are considerably different from the spectrum of adamantane.
Mass spectrometry in structural and stereochemical problems–CLXXXIX: Electron‐impact induced fragmentations and rearrangements of alkoxycyclohexanol trimethylsilyl ethers and alkoxycyclohexyl trimethylsilanes
Authors: Gray Robin T. , Diekman John , Larson G. L. , Musker W. K. , Djerassi Carl
Published: May 2005

In view of the current interest in the electron‐impact induced rearrangements of both trimethylsilyl derivatives and bifunctionalized cyclohexanes, the mass spectral properties of several alkoxycyclohexanol trimethylsilyl ethers and alkoxycyclohexyl trimethylsilanes have been investigated. Using deuterium labeling, the basic fragmentation modes incurred upon electron‐impact of ethanol trimethylsilyl ether were elucidated. The major peaks in the spectrum of this simple ether occur also in those of the title compounds, the latter fragments having been formed by interaction of the two functional groups. Thus the initial rearrangement ion of mass 103 (e) from electron bombardment of 4‐ethoxycyclohexanol trimethylsilyl ether and 2‐ethoxycyclohexyl trimethylsilane corresponds to the [M  CH3] ion from ethanol trimethylsilyl ether. Its further fragmentation has been studied using high resolution and metastable ion measurements, and the scope of the interaction between the alkoxy and trimethylsilyl groups, when silicon is attached both to oxygen and to carbon, has been determined. In addition, the origin of every ‘characteristic’ fragment ion has been elucidated on the basis of each corresponding peak in the spectra of several derivatives labeled specifically with deuterium. Peaks derived from initial ionization of both functionalities in each compound have been observed, although the majority of ions in the spectra of both series seem to be directed by fragmentations associated with the trimethylsilyl ether moiety.
The mass spectra of reissert compounds
Authors: Popp F. D. , Potts K. T. , Armbruster R.
Published: May 2005

A series of Reissert compounds containing the quinoline, isoquinoline and phthalazine nuclei show the common feature in their mass spectra of the initial loss of the N‐substituent and either of the substituents attached to the adjacent carbon atom.
The structure of [YC6H6N]+˙ ions in the spectra of substituted acetanilides
Authors: Gamble A. A. , Gilbert J. R. , Tillett J. G.
Published: May 2005

Evidence is adduced from steric effects on relative intensities that the [YC6H6N]+ ions from substituted acetanilides have the aniline structure.
Fragmentations de Molecules Aliphatiques Bifonctionnelles: Aminoesters a Longue Chaine
Authors: Caspar Alain , Teller Gérard , Wolff Robert E.
Published: May 2005

L'élimination de CH3OH à partir d'un des ions de coupure α produits par la fragmentation des esters des aminoacides à longue chaîne est induite par l'interation des deux fonctions même lorsque celles‐ci sont éloignées l'une de l'autre dans la molécule. Elle met en cause en partie un atome d'hydrogène du groupe NH2, en partie un atome d'hydrogène du CH2 en α du carbone qui porte le groupe NH2. Des mécanismes sont proposés et une comparaison est faite avec les fragmentations des ω‐aminoesters, déjà étudiés.
The mass spectra of some phenanthro (9,10‐d) heterocycles
Authors: Cooper J. L. , Lipsky S. R. , McMurray W. J.
Published: May 2005

The mass spectra of six phenanthro(9,10‐d)‐oxazoles, thiazoles and imidazoles are reported. The decompositions of the phenanthro(9,10‐d) derivatives resemble the corresponding benzo heterocycles. A C13H7 fragment was found to be characteristic of these phenanthro compounds. Deuterium labeling was used to show that there is no correlation between the formation of the C13H7 from the phenanthro compounds and the C13H9 observed in the spectra of 4,5‐diphenyl substituted heterocycles.
The ‘preference factor’ and isotope effect in the loss of hydrogen or deuterium from labeled toluenes
Authors: Beynon J. H. , Corn J. E. , Baitinger W. E. , Caprioli R. M. , Benkeser R. A.
Published: May 2005

Metastable ion decompositions involving the loss of hydrogen and deuterium from partially deuterated toluene ions were studied using a double focusing mass spectrometer. The electric sector voltage was adjusted so that the only ions transmitted were those which lost a particular fraction of their kinetic energy in decompositions taking place in front of the electric sector. Transitions involving loss of mass 1 or mass 2 from the molecular ions of toluene‐α‐d3 and toluene‐2,3,4,5,6‐d5 were studied. The results showed that in these slow reactions, the ‘preference factor’ defined as the ratio of the probability of loss of a hydrogen atom from a side‐chain position to loss of a hydrogen atom from a ring position was 1.00. The ‘isotope factor,’ defined as the ratio of the probability of loss of a hydrogen atom from any position to that for the loss of a deuterium atom from the same position was found to be 3·50.
Mass spectral and pyrolytic fragmentation paths for o‐nitroanisole
Authors: Mamer O. A. , Kominar R. J. , Lossing F. P.
Published: May 2005

The mass spectral and pyrolytic dissociations of o‐nitroanisole are reported. The parent ion dissociates by two pathways, principally through loss of CH2O, but a significant fraction through loss of NO. The parent‐less‐30 peak is therefore a doublet, as shown by high resolution measurements. The thermal decomposition at 600°C and above proceeds also by two pathways, but these are the loss of HNO and HNO2, to form 1,2‐methylenedioxybenzene and benzaldehyde respectively.
The mass spectra of some diterpene lactones
Authors: Hodges R. , Cambie R. C. , Joblin K. N.
Published: May 2005

The molecular ions of some diterpenoid trans‐γ‐and δ‐lactones have been shown to lose the elements of carbon dioxide. The corresponding cis‐lactones do not undergo fission in this manner. A mechanism for this stereospecific fragmentation is proposed.
Kinetic shifts and metastable transitions
Authors: Hickling R. D. , Jennings K. R.
Published: May 2005

Differences in the appearance potentials of normal fragment ions and of metastable transitions leading to the formation of the same fragment ions have been measured in the mass spectra of a number of compounds. The differences varied from 0.1 to 1.0 eV and were attributed to the measurable part of the kinetic shift. An approximate correlation was found between the intensity of a ‘metastable peak’ and the observed difference in appearance potentials, and it is suggested that the full kinetic shift for processes giving rise to intense ‘metastable peaks’ is substantially larger than the measurable part. The implications of this in thermochemical calculations are discussed.
Calculation of mass spectra of some organic compounds undergoing two consecutive reactions from the molecular ions
Authors: Yeo Adrian N. H. , Williams Dudley H.
Published: May 2005

The molecular ions of phenyl benzoate, methyl benzoate, t‐butylbenzene, phthalic anhydride, p‐dimethoxybenzene, o‐dimethoxybenzene and acetophenone each undergo two consecutive reactions ([M]+.→[A]+→[B]+). These unimolecular reactions are treated within the framework of the quasi‐equilibrium theory (QET); a simple modification of the original equation relating the rate constant (k) with the internal energy (E) was used to calculate mass spectra of the above compounds from 12 to 20 eV. Good agreement between calculated and observed spectra is obtained.
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

The 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

Studies 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

Benzene, 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

The 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

The 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

The 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

Mass 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

The 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

Requirements 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

The 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

The 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

The 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

A 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

The 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

The 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

The 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

The 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

The 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

[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

Complete 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

The 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

Ion 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

The 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

The 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

The 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

Extensive 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

The 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

The 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

A 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

The 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

The 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

The 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.
Mass spectra of methines of the benzylisoquinoline alkaloids
Authors: Dolejš L. , Slavík J.
Published: May 2005

Mass spectra of the stilbene type methines of the benzylisoquinoline alkaloids exhibit high melecular peaks and show structurally characteristic fragmentation patterns.
The high resolution mass spectrum of 2‐acetamido‐1,3,4,6‐tetra‐O‐acetyl‐2‐deoxy‐α‐D‐glucopyranose
Authors: Dougherty Ralph C. , Horton Derek , Philips Kerstin D. , Wander Joseph D.
Published: May 2005

2‐Acetamido‐1,3,4,6‐tetra‐O‐acetyl‐2‐deoxy‐α‐D‐glucopyranose (I), and its analogs specifically mono (trideuterioacetylated) at O‐1 (III), at N‐2 (II), at O‐4 (IV) and at O‐6 (V), have been examined by high‐resolution mass spectrometry. From the elemental compositions of the fragment ions, the mass‐number shifts resulting from deuterium incorporation and analysis of metastable transitions, it has been possible to specify in detail the fragmentation pathways undergone by this molecule. The principal degradations of I proceed by initial rapid decomposition of the molecular ion (whose intensity is insignificant) by three routes: (i) by loss of the C‐1 acetoxyl group as a radical to give the glycosyl cation (a), (ii) by loss of the 1‐acetyl group as a radical to give an acyclic ion m/e 346 (b) and (iii) by loss of a C‐6 fragment and acetic acid derived from the 3‐acetate group to give m/e 241 (c).
The negative ion mass spectra of methanol and deuterated methanol
Authors: Thynne J. C. J.
Published: May 2005

The negative ion mass spectra of methanol, methanol‐d and trideuteromethanol have been measured at 70 eV. Use of deuterated methanols has enabled the ion at m/e 31 to be identified as CH3O− and not CH2OH−. Isotope effects have been determined for H− and D− formation, and for OH− and OD− formation. It has been shown that OH− formation occurs as a rearrangement reaction as well as by simple CO bond fission.
Preferred electron‐impact elimination of two CHO groups from A triapentafulvalenequinone. Formation of a triafulvalene radical cation?
Authors: Agranat Israel
Published: May 2005

The mass spectral fragmentations of 1,2‐diphenyl‐ and 1,2‐di (phenyl‐d5)‐4,5‐benzotriapentafulvalene‐3,6‐quinone indicate the preferred elimination of two CHO groups with the formation of triafulvalene radical cations.
Ionisation and appearance potentials in the evaluation of nonbonded interactions—IV: Conformational effects in methyl‐substituted 1,3‐oxathianes
Authors: Jalonen Jorma , Pasanen Paavo , Pihlaja Kalevi
Published: May 2005

The ionization and appearance potentials for the molecular and [M  Me]+ ions of several stereoisomeric methyl‐1,3‐oxathianes were measured. The differences between the ionisation and/or appearance potentials are shown to correlate well with the conformational energy differences in question.
Negative ion mass spectrometry—I: The spectra of some stabilised alkylidenetriphenyl‐phosphoranes
Authors: Alexander R. G. , Bigley D. B. , Todd J. F. J.
Published: May 2005

The 70 eV negative ion mass spectra of a series of phosphoranes exhibit significant peaks for ions resulting from skeletal rearrangements. The primary fragmentation reactions of the molecular anions, which involve reduction of the phosphorus from the penta‐ to the ter‐valent state, have been rationalised in terms of the relative stabilities of the products formed. The processes occurring are in some cases analogous to and in other cases complementary to, those previously observed in the positive ion spectra of similar compounds.
Elektronenstossinduzierte fragmentierung von polymethylbenzaldehyden—III: Bildung und Zerfall des Formyltropylium‐ions aus Dimethylbenzaldehyd
Authors: Schwarz Helmut , Bohlmann Ferdinand , Vorlaender Wolfgang
Published: May 2005

Die elektronenstossinduzierte Bildung des sehr instabilen ‘formyltropylium‐Ions’ aus Dimethylbenzaldehyd kann durch den Mechanismus einer vinylogen α‐Spaltung erklärt werden.
Electron‐impact‐induced rearrangements of organic ions–II:1 Unimolecular decompositions of some isomeric [C9H10H]+ metastable ions
Authors: d'Alcontres Guglielmo Stagno , Cum Giampietro , Uccella Nicola
Published: May 2005

[C9H10N]+ cations (m/e 132) are generated by electron‐impact from structurally distinct compounds within a mass spectrometer. They undergo three metastable fragmentation processes, preceded by isomerisation reactions of the precursor ions. The kinetics and energetics of the unimolecular reactions involved are discussed.
Massenspektrometrische Untersuchung von Amiden–I: Energetische Betrachtungen zur el Ektronenstosin‐Duzierten Fragmentierung von Piperidin‐ und Piperidein‐ Amiden
Authors: Schwarz Helmut , Bohlmann Ferdinand
Published: May 2005

Die Aktivierungsenergie für die Bildung von [RCO]+‐Ionen aus verschiedenen Piperidin und Piperidein‐Amiden wird ermittelt und ein Zusammenhang mit der CN‐Bindungsenergie der A‐midfunktion diskutiert. Ausserdem wird ein cyclischer Fragmentierungs‐mechanismus mit Hilfe energetischer Gesichtspunkte begründet.
Mechanismus der elektronenstossinduzierten Äathylenabspaltung aus dem Ion [C9H11]+ aus 2,5‐Dimethylbenzylbromid
Authors: Schwarz Helmut , Köoppel Claus , Bohlmann Ferdinand
Published: May 2005

Die Untersuchung von 13C‐markiertem Dimethylbenzylbromid zeigt, dass dem [M – Br]+‐Ion die Struktur eines Dimethyltropylium‐Kations zukommt.
The mass spectra of some N‐substituted barbitals and their trimethylsilyl derivatives
Authors: Watson J. Throck , Falkner Fred C.
Published: May 2005

The mass spectra of N‐propyl and N‐butyl barbitals show the loss of olefin radical (CnH2n‐1) in analogy to structurally similar molecules such as N‐alkyl succinimides and 3‐alkyl uracils. Trimethylsilylation of the N‐substituted barbitals suppresses this fragmentation and loss of olefin via apparent McLafferty rearrangement from the even‐electron ion, [M – 15]+, becomes significant. The trimethylsilyl derivatives of N‐allyl barbital and N‐phenyl barbital show an unusually facile elimination of the appropriate isocyanate from the molecular ion.
The effect of stereochemical peculiarities on the electron‐impact‐induced fragmentation of matridine and its stereoisomers
Authors: Wulfson N. S. , Ziyavidinova Z. S. , Zaikin V. G.
Published: May 2005

With the aid of the mass spectra of 14,14‐d2 analogues the majority of the m/e 98 ions in the spectrum of allomatridine were shown to contain ring D, whereas in the case of matridine and isosophoridan the m/e 98 ions mainly include rings A or B. The m/e 84 ion results mostly from a charge localisation on ring D for allomatridine and isosophoridan, while in the case of matridine it may arise due to charge localisation on ring D accompanied by migration of the 14‐H atom from the charged fragment, as well as on rings A or B with a hydrogen atom migrating to the charged species.
Substituent and H/D randomization in the mass spectra of substituted diphenylacetylenic compounds
Authors: Safe S.
Published: May 2005

The mass spectra of several substituted diphenylacetylenes are reported and the [metastable ion]/[daughter ion] ratios for the isomeric chloro‐ and bromodiphenylacetylenes suggested substituent scrambling in their respective molecular ions. The metastable ion data also indicated equilibration of the chloro substituents in a series of isomeric dichlorodiphenylacetylenes. In addition, the fragmentation patterns for the amino‐ and nitrodiphenylacetylenes differed somewhat from most other aromatic amino and nitro compounds. The aminodiphenylacetylenes fragment with expulsion of H2CN from the molecular ion and the expulsion of HCN from the [M – 1]+ ion was only a relatively minor reaction. 4‐Nitrodiphenylacetylene loses NO from the molecular ion and OH from the [M – NO]+˙, whereas the more familiar loss of OH from the molecular ion was not observed. The mass spectra of several deuterated substituted diphenylacetylenes clearly showed extensive (but not complete) H/D equilibration in the molecular ion or some subsequent decomposition ion. Comparative studies between 4‐chloro and 4‐bromo substituted biphenyl, diphenylacetylene and diphenyldiacetylene indicated similar degrees of H/D randomization, and the results showed that the CC group did not inhibit the proton equilibration between the two phenyl groups.
Electron‐impact spectra of ms‐tetra‐phenylchlorins and the stability of chlorins
Authors: Meot‐Ner M. , Adler A. D. , Green J. H.
Published: May 2005

The mass spectrum of ms‐tetraphenylchlorin was observed to contain a significant porphyrin peak. Attempts to obtain metallochlorin spectra yeilded mainly metalloporphyrin spectra. Sublimation experiments established that the chlorin to porphyrin conversion resulted from electron‐impact excitation and did not arise from thermolysis on the probe or from impurities. In conjunction with previous literature data, this is interpreted as showing that the apparent stability of chlorins with respect to porphyrins is mainly a matter of the activation energies required under specific constraints.
Studies in chemical ionization mass spectrometry:Steroidal ketones
Authors: Michnowicz John , Munson Burnaby
Published: May 2005

The CH4 chemical ionization (CI) spectra of several keto‐steroids are reported as well as the H2 and C3H8CI spectra of a few keto‐steroids. [M + H  H2O]+ is an abundant ion in the CH4CI spectrum of 5α‐androstane‐17‐one and the water loss from the [M + H]+ ions does not involve the hydrogens on C‐18 and only involves the C‐16 hydrogens to about 10%. The major loss process has not been determined.3‐Keto and 17‐Keto steroids are readily distinguished by their CH4CI spectra. The effectiveness of substituents for directing attack by [CH5]+ and [C2H5]+ can be estimated:carboxyl > methoxy ≃ carbonyl > bromo ≃ chloro > hydroxy. Significant differences are observed in the H2CI spectra of two 5α‐vs. 5β‐steroids. Propane CI Spectra are similar to methane CI spectra, but show generally less fragmentation.
Positive ion fragmentation mechanisms of some simple aldehydes and epoxides and trimethylene oxide
Authors: Pritchard J. G.
Published: May 2005

The metastable ion spectra of ethylene oxide, acetaldehyde, acetaldehyde‐d4, propylene oxide, propionaldehyde and trimethylene oxide are presented. They reveal no reason to suppose that electron‐impact‐induced isomerisation of oxide to aldehyde structure occurs, although many spectral features are common to various members of this set. The spectra of phenylacetaldehyde and styrene oxide are compared, and the more plausible possibility of partial isomerisation in this case is discussed.
Mass spectral fragmentation studies in usnic acid and related compounds
Authors: Kutney James P. , Sanchez Ignacio H. , Yee Trevor H.
Published: May 2005

A study of the fragmentation patterns of the naturally occurring lichen substance, usnic acid (I) and various other chemically and biochemically derived compounds is reported and discussed. From these results it is demonstrated that the characteristic fragmentation patterns observed are of considerable utility in determining not only the substitution patterns on these highly oxygenated molecules, but also the structural elucidation of new compounds within the series.
Steric strain and electron‐impact. The behaviour of some n,n'‐dimethyl‐1,1‐binaphthyls, some n,n'‐dimethylbiphenyls and model compounds
Authors: Loudon A. G. , Mazengo R. Z.
Published: May 2005

For the title compounds I(M), A[M  H]+ and A[M  Me]+ have been determined. In the biaryl compounds, unlike the xylene and the two dimethylnaphthalenes studied, A[M  Me]+ is noticeably dependent on the position of the methyl group. Deuterium labelling of the methyl groups in the biaryl compounds reveals that more than one process is involved in the formation of the [M  Me]+ ion. In contrast, only in the case of 2,2′‐dimethylbiphenyl is the appearance potential of the [M  H]+ ion position dependent. The labelling results suggest complete scrambling of the hydrogen atoms before formation of the [M  H]+ ions. Some comments are made on the problem of trying to relate differences in strain energies and ionisation and appearance potentials in alkyl substituted aromatics.
Spectrometrie de Masse des Epoxydes Phenyles—II
Authors: Fetizon Marcel , Henry Yannik , Aranda Gérard , Audier Henri‐Edouard , De Luzes Hugues
Published: May 2005

Les époxydes aromatiques se fragmentent soit directement par élimination d'une molécule d'aldéhyde ou de cétone pour donner un ion symétrique soit aprés réarrangements de l'ion moléculaire en composés carbonylés. Les substituants du noyau ont une trés grande influence sur les fragmenta‐tions.
Thermal decompositions of N‐methylpyridinium, quinolinium, isoquinolinium and phenanthridinium salts in a mass spectrometer. Evidence for a specific HI elimination and for an oxidation to amides
Authors: Salsmans R. , Van Binst G.
Published: May 2005

The mass spectra of some N‐methylpyridinium, quinolinium, isoquinolinium and phenanthridinium salts (R+X−)

The salt will be represented by R+X− or RX, R+ being the organic moiety, with its associated mass and X‐ the inorganic anion.

are analyzed (X− = I− or ClO4−). For X− = I−, thermal decomposition gives rise mainly to the superimposed spectra of CH3I and the free base. Hence, iodide salts cannot be determined specifically by their mass spectra. When an α‐methyl group is present, e.g. 2‐methylpyridinium methiodide, elimination of HI becomes an important thermal process. For X− = ClO4−, the same pattern is observed, but in addition a generally important peak at [R + 15] is present. This peak is due to the oxidation, mainly α to the nitrogen of the organic moiety by the ClO4− ion, giving rise to the corresponding amide. In some cases, chlorination of the organic moiety has been observed as well as double oxidation. The thermal processes for the perchlorate salts are characteristic and are useful in the elucidation of the quaternary structure.
Mass spectra of benzenesulfonylhydrazides
Authors: Balza Felipe , Duran Nelson
Published: May 2005

The mass spectrometry of substituted benzenesulfonylhydrazides (X.C6H4.SO2NHNH2) has been studied, with X = p‐CH3, H, p‐CH3O and p‐Br. The intensities of [XC6H4SO2]+ and [XC6H4]+ follow the Hammett relationship [In(Z/Z0) =ρδp+] with ρ of 0.375 and 2.37, respectively.