bluuebunny/crossref_metadata_2025 huggingface dataset:
Charge localization in the retro‐Diels‐Alder fragmentation of tetralins
Authors: Lightner D. A. , Steinberg Frank S.
Published: May 2005

The electron‐impact induced retro‐Diels‐Alder reaction of 5‐ and 6‐substituted tetralins has been examined. Most electron‐donating groups at C‐5 retard the fragmentation relative to tetralin; whereas, electron‐withdrawing groups slightly increase the fragmentation.
Kinetic studies in mass spectrometry–VII: Competing cleavage and rearrangement processes in molecular ion decomposition reactions
Authors: Brown Peter
Published: May 2005

Apparently competing cleavage and rearrangement reactions in a series of molecular ions have been studied by ionization and appearance potential methods, and by determination of the electron energy dependence of both normal and metastable daughter ion peak intensities. The processes investigated were (i) [M  CH3] vs. [M  CH2O] in anisole; (ii) [M  OC6H5] vs. [M  CO] in phenyl ether; (iii) [M  NO2] vs. [M  NO] in nitrobenzene; (iv) [M  C3H7] vs. [M  C2H4] in butyrophenone: (v) [M  C3H7] vs. [M  C3H6] in n‐butylbenzene; (vi) [M  CH2OH] vs. [M  CH2O] in 2‐phenylethanol; (vii) [M  CH3CO2] vs. [M  CH2CO] in benzyl acetate; and (viii) [M  C4H9O] vs. [M  C4H7] in n‐butylbenzoate. The results are interpreted in terms of k vs. E curves with very different frequency factors for the two reaction types. Appearance potentials of metastable ions for the rearrangement reactions have also been measured.
Mass spectrometry in structural and stereochemical problems–CXCIV: The mass spectrometric fragmentations of steroidal sapogenins
Authors: Faul William H. , Djerassi Carl
Published: May 2005

The characteristic mass spectral fragmentation patterns of the basic structure of the steroidal sapogenin, (25R)‐5α‐spirostan, have been elucidated through the preparation of analogs with deuterium labels at positions 11, 12, 14, 15, 16, 17, 20, 21, 23, 24, 25, 26 and 27. In addition, the effects of a change of stereochemistry at positions 14 and 20, of the introduction of oxygencontaining functionalities mostly in ring F, and of the incorporation of olefinic unsaturation have been determined through synthesis of many examples.
Mass‐spectrometric studies on alkylated 6‐thiopurines
Authors: Deutsch Joseph , Neiman Zohar , Bergmann Felix
Published: May 2005

6‐Thiopurine and its N‐ or C‐alkyl derivatives all form an [M – 1]‐ion upon fragmentation. In the 7‐alkyl derivatives, this ion represents the major component of the spectrum. This is ascribed to formation of a five‐membered thiazoline‐like ring. Similar ring formation stabilises the [M – 1]‐ion in the 7‐methyl derivatives of hypoxanthine, adenine and 6‐selenopurine.
Mass spectral fragmentations of aminoketones in which charge is not localized exclusively on nitrogen
Authors: Wagner Peter J.
Published: May 2005

The low resolution mass spectra of α‐dimethylaminoacetophenone and γ‐dimethylaminobutyrophenone are compared to those of δ‐methylhexanophenone and dimethyl n‐butylamine as well as to those of α‐dimethylaminoacetonitrile and γ‐dimethylaminobutyronitrile. Analysis indicates that significant fractions of the fragmentations of the aminoketones are directed by the carbonyl. In particular, McLafferty rearrangement of the γ‐aminoketone is favored over α‐cleavage from nitrogen at ionizing voltages below 15 eV. Although the overall fragmentation patterns are presumably determined both by the distribution of charge and by the relative rates of the fragmentation processes available to the two ionized groups, the intrinsic rates for α‐cleavage at ionized nitrogen and at ionized carbonyls appear to be very similar. Kinetic analysis suggests that 26% of the charge resides on the carbonyl in the γ‐aminoketone molecular ion. The extent of delocalization of charge in any aminoketone may be partially controlled by the extent of spatial overlap of the two groups. Correlations of mass spectral behavior with photochemical behavior are thus limited because electronic excitation is more localized in the lowest excited states of molecules than charge is in electron‐impact produced molecular ions.
Electron‐impact‐induced ring condensation. The mass spectra of some aryl‐alkyl diethers
Authors: Vouros P. , Biemann K.
Published: May 2005

The mass spectra of catechol polymethylene diether homologs have been determined and the formation of unexpected fragment ions is reported. The size of the aliphatic ring significantly influences the relative intensity of the various ions produced. Possible mechanisms involving a ring contraction process are suggested to explain the formation of one of the common ion fragments (a) in the homologous series. Deuterium labeling experiments indicate that fragment ion a is formed by participation of the α carbons, but extensive isotope scrambling prevents the establishment of a concrete mechanism for the formation of the common catechol ion fragment (m/e 110).
On the loss of ammonia from phenylalkyl amines
Authors: Lightner D. A. , Sunderman F. W. , Hurtado L. , Thommen E.
Published: May 2005

The molecular ion‐minus‐ammonia [M – NHJ] fragmentation of (3‐phenylpropyl) primary amines is a major contributor to the total ion current. This fragmentation occurs to a lesser extent in the lower and higher homologs, (2‐phenethy1)‐ and (4‐phenylbuty1)amine. The loss of methylamine and dimethylamine from N‐methyl‐(3‐phenylpropyl)amine and N,N‐dimethyl‐(3‐phenylpropy1)amine respectively is essentially absent. Deuterium labeling has shown that C‐3 is the primary source of hydrogen abstracted in the [M  NHJ] fragmentation of (3‐pheny1propyl)amine.
The mass spectra of phenothiaphosphine derivatives
Authors: Granoth I. , Kalir A. , Pelah Z. , Bergmann E. D.
Published: May 2005

The molecular ion of the phenothiaphosphine derivatives is fairly stable. Under electronimpact, the phenothiaphosphines (I) and phenothiaphosphinic acids (IV, R = H) undergo a one‐step elimination of the phosphorus atom together with the groups attached to it. Substitutents in the aromatic rings, as well as on the phosphorus, influence the fragmentation pattern; ring methyl, e.g. leads to tropylium structures. Phosphine oxides of type V lose RO˙, probably after a rearrangement, when R = aryl, but R˙ if it is methyl.
Mass spectrometry of onium compounds—II. Carnitine and O‐acyl derivatives
Authors: Hvistendahl Georg , Undheim Kjell , Bremer Jon
Published: May 2005

Carnitine and its O‐acyl derivatives undergo two major pyrolytic reactions in the mass spectrometer. Firstly elimination of water from carnitine or acid from acylcarnitine takes place followed by intramolecular displacement and formation of crotonyl lactone and trimethylamine. Secondly intramolecular displacement occurs with formation of a substituted γ‐lactone and trimethylamine. For the lower acid derivatives only the elimination pathway is important. For carnitine and higher derivatives both processes are important.

The electron induced fragmentations of the major pyrolysis products are relatively simple. The most important pathways for the major components are discussed.

The pyrolytic composition and mode of fragmentation are characteristic and can be used for identification purposes.
A technique of molecular formula determination by mass spectrometry
Authors: Sakurai Hiroshi , Tatematsu Akira , Nakata Hisao
Published: May 2005

An improved method of molecular formula determination without any standard sample is proposed. 2‐Aminopyridine was examined as an example and unambiguous molecular formula determination was made.
Benzyl vs. tropylium ions in the decomposition of some alkylnitrobenzenes
Authors: Westwood R. , Williams Dudley H. , Yeo Adrian N. H.
Published: May 2005

The [NO2C7H6]+ ions generated from m‐alkylnitrobenzenes have been shown to be different in their decomposition from those generated from p‐alkylnitrobenzenes, even when the alkyl group is methyl and the departing fragment a hydrogen radical. Thus, in these cases even molecular ions of relatively high internal energy do not reversibly ring‐expand to cycloheptatriene structures. In addition, the [NO2C7H6]+ ions, assumed to be benzylic, do not ring‐expand to nitrotropylium ions at internal energies sufficient to cause subsequent loss of NO or NO2 from the p‐ and m‐isomers, respectively.
Carbon skeletal rearrangement and hydrogen migration in thiophene
Authors: de Jong F. , Sinnige H. J. M. , Janssen Matthijs J.
Published: May 2005

The mass spectra of 13C‐labelled thiophenes were studied and the label‐distributions for the C3H3⊕, HCS⊕, C2H2S⊕ and [M  CH3]⊕ ions are interpreted in terms of a carbon skeletal rearrangement. From a comparison of the results of 13C‐labelling and D‐labelling, a concurrent hydrogen migration process is demonstrated. The production of HCS⊕ ions is preceded by partial carbon scrambling and hydrogen migration is of minor importance. In contrast, hydrogen scrambling predominates over carbon scrambling in the loss of acetylene.
Mass spectral fragmentation patterns of isomeric s‐Triazolo[4,3‐a]pyridines and s‐triazolo[1,5‐a]pyridines
Authors: Potts K. T. , Brugel E. , Singh U. P.
Published: May 2005

The major decomposition pathway involved in the fragmentation of derivatives of the title ring systems was the loss of RCN from the five‐membered ring, except when this ring had a 3‐amino,3‐hydroxyl or 3‐mercapto substituent. In these cases, the exocyclic substituent and at least one nitrogen atom from the five‐membered ring were lost.
The mass spectrometry of kaurene derivatives—II: Kaurenolides and related systems
Authors: Kalinovsky A. I. , Serebryakov E. P. , Simolin A. V. , Kucherov V. F. , Chizhov O. S.
Published: May 2005

The mass spectra of a number of natural (II, IV, XII) and modified kaurenolides (I, III, V to XI) are reported. The major fragmentations of these compounds occur by rupture of the ring B to give fragments B and C, both of which contain the ring A. In the case of the 7‐hydroxycompounds (II and III) their mass spectra are markedly different due to the difference in configuration at C7.
Negative ion mass spectrometry of the new riboflavin metabolite: 7,8‐dimethyl‐10‐formylmethyl‐isoalloxazine ethyl‐hemi‐alcoholate (flavin‐10‐acetaldehyde ethyl‐hemi‐alcoholate)
Authors: Tümmler R. , Steinfelder K. , Owen E. C. , West D. W.
Published: May 2005

Flavin‐10‐acetaldehyde ethyl hemi‐alcoholate obtained at the Hannah Dairy Research Institute by bacterial degradation of riboflavin was examined in the Electron Attachment (EA) apparatus at the Forschungsinstitut Manfred von Ardenne. At low temperatures pyrolysis was negligible and the peak of greatest mass was only four units less than the molecular weight. The fragmentation patterns at greater field strengths indicated metastable peaks of masses in accord with the fragmentation pattern at lower fields. The patterns at the lower temperatures used resembled in important respects the EA pattern from riboflavin in an earlier study. In explanation of the fragmentation pattern obtained, structures have been assigned to the ions recorded.
The mass spectra of N‐acyliminopyridinium and isoquinolinium betaines
Authors: Ikeda M. , Tsujimoto N. , Tamura Y.
Published: May 2005

The mass spectral fragmentation behaviour of N‐acyliminopyridinium and isoquinolinium betaines has been investigated. Major fragmentations of the pyridinium betaines can be rationalized in terms of charge localization on the pyridinium nitrogen. The most prominent process is α‐cleavage followed by loss of NCO to furnish a pyridine ion. The electron‐impact induced fragmentation of N‐benzoyliminopyridinium betaine (I) was compared with that of thermolysis. The completely analogous behaviour has been observed in the corresponding isoquinolinium betaines.
A new mass spectrometric classification of alkylbenzenes
Authors: Gillis R. G.
Published: May 2005

A classification of alkylbenzenes is proposed based on the relative intensities of pairs of ions, of which one is formed from the other by loss of a hydrogen molecule.
The mass spectrum of tropylium fluoroborate
Authors: Gardner R. J.
Published: May 2005

The mass spectrum of tropylium fluoroborate (C7H7+BF4−) shows a base peak corresponding to the cationic portion of the salt (m/e91) and intense peaks occur at m/e 109 (C7H6F+) and m/e 110 (C7H7F+.). The latter peaks are probably of thermal origin. A similar rearrangement is observed in trityl fluoroborate (C19H15+BF4−) and may be a general feature of the mass spectra of aromatic fluoroborates.
Alcaloïdes stëroïdiques—cxi Influence D'un Groupement Hydroxyle sur la Fragmentation D'amines, Amides et Imines Stéroïdiques en Spectrométrie de Masse
Authors: Longevialle P. , Einhorn J. , Alazard J. P. , Diatta L. , Milliet P. , Monneret C. , Khuong‐Huu Q. , Lusinchi X.
Published: May 2005

La prtsénce d'un groupement hydroxyle dans les molécules de certaines amines, amides et imines stéroídiques joue un grand rôe dans la fragmentation de celles‐ci en spectrométrie de masse. Cette fragmentation est initiée par le transfert, parfois à longue distance, de l'hydrogéne hydroxylique sur les groupements azotés et donne naissance à des ions caractéristiques de la place de l'hydroxyle.
Mass spectra of some furanosesquiterpenes
Authors: Das K. G. , Nayar M. S. B. , Joshi B. S.
Published: May 2005

Some of the fragmentation modes operating in a few furanosesquiterpenes have been established from accurate mass measurements and metastable data.
Correlation of structure and fragmentation modes of costunolide and its derivatives
Authors: Sathe R. N. , Deshpande S. N. R. , Kulkarni G. H. , Kelkar G. R. , Das K. G.
Published: May 2005

Mass spectral studies on costunolide and lactones derived therefrom, have revealed some general fragmentation modes involving the losses of 44, 55, 57, 59, 71, 73 and 83 mass units from the molecular ion. The probable genesis of these ions is established by high resolution, metastable transitions and deuterium labelling studies. Comparison has been made with the mass spectra of some C6‐ desoxy esters.
The elucidation of the primary structure of the hypothalamic thyroid stimulating hormone releasing factor of ovine origin by means of mass spectrometry
Authors: Desiderio Dominic M. , Burgus Roger , Dunn Thomas F. , Vale Wylie , Guillemin Roger , Ward Darrell N.
Published: May 2005

This paper illustrates the role that mass spectrometry played in the first elucidation of the primary structure of a hypothalamic releasing factor. It has been demonstrated that ovine TRF has the structure 2‐pyrrolidone‐5‐carboxylyl‐histidyl‐proline amide.
Electron‐impact induced fragmentation of partially fluorinated β‐diketones
Authors: Rubesch M. , Clobes A. L. , Morris M. L. , Koob R. D.
Published: May 2005

The ionic fragmentation of twelve partially fluorinated β‐diketones, RCOCH2COCF3 was studied with a medium resolution mass spectrometer. In addition to the anticipated fragmentation by β‐cleavage, a number of interesting rearrangements are observed. [CF3COCH2CO]+., an ion common to all of the compounds investigated, decomposes predominantly by elimination of HF. When R is an alkyl group containing hydrogen γ to the adgacent carbonyl, the McLafferty rearrangement occurs. The [RCOCH2CO]+.ion eliminates neutral RH when R is phenyl, thienyl, or cyclopropyl. An intense metastable peak, absent when R is an alkyl substituent, accompanies the rearrangement in these three compounds. A number of fragments characteristic of the R substituent are also observed in many cases. This is interpreted as indicating a considerable degree of charge localization on the R moiety.
The behaviour of perchloro‐3,4‐dimethylenecyclobutene,‐pentafulvene and‐ pentafulv‐alene under electron‐impact
Authors: Agranat Israel , Loewenstein Ruth M. J. , Bergmann Ernst D.
Published: May 2005

The mass spectra of 1,2‐dichloro‐3,4‐bis(dichloromethylene)cyclobutene (IV) and of hexachloropentafulvene (II) have been studied. Compound IV cannot be an intermediate in the formation of II from octachloro‐1,2‐dimethylenecyclobutane (III) under electron‐impact, as previously suggested. In the mass spectra of II and IV the species [C6]+ and [C5]+ occur, obviously through cleavage of the semicyclic C‐C bond.

The mass spectrum of pentachlorofulvalene (VI) shows strikingly that successive elimination of an even number of CI atoms is preferred over that of an odd number of CI atoms; probably corresponding C‐CI bonds in the two rings are broken simultaneously. Amongst the fragments, the species [C10]+ and [C7]+ and possibly also [C8]+ and [C9]+ have been observed.
Gas chromatographic and mass spectrometric characteristics of some bicyclic thioketones
Authors: Campbell M. M. , Anthony G. M. , Brooks C. J. W.
Published: May 2005

Three bicyclic thioketones were examined by combined gas chromatography‐mass spectrometry. Deuterium labelling was employed in the interpretation of the fragmentation processes in thiocamphor. Compared with the oxygen analogues, the thiones yielded on electron‐impact a higher proportion of characteristic fragment ions containing the hetero‐atom.
Rearrangements in the electron‐impact induced fragmentation reactions of 5‐alkylthio‐1,3,4‐thiadiazolyl‐2‐amines
Authors: Barnes C. S. , Goldsack R. J. , Rao Ravindra Pratap
Published: May 2005

The low resolution mass spectra of a number of homologous 5‐alkylthio‐1,3,4‐thiadiazolyl‐2‐amines have been determined. With the methylthio compound the only significant loss from the molecular ion is the sulphydryl radical. As the homologous series is ascended this reaction becomes less important and is insignificant with the butylthio isomers. The ethylthio compound suffers extensive loss of ethylene and when the alkyl group contains three or more carbon atoms the main reaction is always loss of the olefin coresponding to the alkyl group.All of the n‐alkylthio compounds showed in addition loss of methylthio radical from the molecular ion. A mechanism is proposed and comparisons made with alkyl phenyl thioethers and alkylthio substituted heterocycles.
A new method for the calculation of molecular formulae from accurate mass data and vice versa
Authors: Moss G. P.
Published: May 2005

A calculator is described for the rapid manual conversion of accurate mass data into molecular formulae. The method uses any information available about the ion to simplify the process. Calculation of accurate masses from a molecular formula is even more rapidly determined.
The mechanism of hydrogen randomization in the stilbene molecular ion
Authors: Güsten H. , Klasinc L. , Marsel J. , Milivojević D.
Published: May 2005

Hydrogen randomization of the stilbene molecular ion preceding the formation of the [M—methyl]‐ion is discussed.
Electron‐impact induced hydrogen scrambling in cyclohexanol and methylcyclohexanols
Authors: Shapiro Robert H. , Levine Steven P. , Duffield A. M.
Published: May 2005

Exact mass measurements and the mass spectral behavior of O‐deuterated cyclohexanols, coupled with a re‐evaluation of previously published data1,2, show that the hydrogen attached to oxygen undergoes partial scrambling with the 2, 3, 5 and 6 position ring hydrogens prior to or during the formation of the major primary fragment ions.
Fluorinated carbohydrates—IX The mass spectra of deoxyfluorohexopyranose derivatives
Authors: Chizhov O. S. , Kadentsev V. I. , Zolotarev B. M. , Foster A. B. , Jarman M. , Westwood J. H.
Published: May 2005

The mass spectra of some deoxyfluorohexopyranose acetates bearing the fluorine substituent at positions 2,3,4, or 6 were determind. The fragmentation pathways were analogous with those for hexopyranose acetates, except that the cleavage of bonds between carbon atoms was hindered by the attachment of a fluorine substituent to one of the carbon atoms.
Heterocyclic studies—XXII. Mass spectra of some 3‐hydroxypteridin‐4‐ones
Authors: Clark Jim , Smith C.
Published: May 2005

Mass spectra of 3‐hydroxypteridin‐4‐one and five of its mono‐and di‐methyl derivatives are recorded. Fragmentation of the non‐methyl compound (I; R1  R2  R3  H) occurred mainly by successive losses of NO, CO, HCN and HCN. Changes in m/e values of the major peaks with methyl‐substitution pattern in the derivatives were consistent with the proposed fragmentation pattern. Several minor fragmentation pathways were also observed but all involved an initial loss from the oxygen containing ring.
Application of mass spectrometry to oligosaccharide sequencing
Authors: Kochetkov N. K. , Chizhov O. S. , Malysheva N. N. , Shiyonok A. I.
Published: May 2005

A recent publication by Johnson et al1. Prompted us to record our earlier findings from mass spectral studies of oligosaccharide (see ref.2). This investigation has shown the possibility of oligosaccharide sequencing by means of the mass spectra of their phenylozotriazoles and N‐arylglycosylamines.
Mass spectra of chloro‐substituted benzophenones
Authors: George W. O. , Hassid D. V. , Phillips J.
Published: May 2005

The mass spectra of all three monochloro‐, seven of the dichloro‐ and two of the trichloro‐substituted benzophenones are reported. The major fragments in the spectra are due to α‐fission to oxonium ions followed by the well‐known subsequent fragmentations. The ring bearing the greater number of chlorine atoms appears to cleave more readily, with 2‐chloro substituents enhancing this tendency. There is evidence for the formation of the biphenylene ion in all monochloro and all dichloro compounds studied and for the formation of the chloro biphenylene ion in both trichloro compounds studied. In the case of 2,2′‐, 2,4‐ and 3,4‐dichlorobenzophenones evidence exists for hydrogen transfer between rings.
Mass spectral evidence for the conversion of benzenephosphonic acid to its cyclic, trimeric anhydride and of benzenephosphonous acid to phenylphosphine
Authors: Wiley Richard H.
Published: May 2005

The mass spectra of benzenephosphonic and benzenephosphonous acids are readily observable under normal operating conditions and, at low sample temperatures (50 to 85°C), the 70 eV electron‐impact degradations are characteristic. The phosphonic acid shows peaks for the molecular ion at 158 amu and for characteristic degradation fragments at 141 (C6H5PO2H), 94 (C6H6O), 78 to 7 (C6H6, C6H5), 65 (H3PO2, C5H5), 51 (C4H3), 47 (PO) and 39 (C3H3) amu. Above 120°, however, and after a pressure surge indicative of a thermal dehydration in the sample, a peak at 420 amu associated with the cyclic, trimeric anhydride, (C6H5PO2)3, is observed along with a characteristic set of fragment peaks at 373, 357, 343, 327, 280, 262, 233, 216 and 199 amu, whose interrelations are summarized in Scheme 1. The phosphonous acid, at 75°C and at 70 eV, shows peaks for the molecular ion at 142 amu and for characteristic degradation fragments at 124 (C6H5PO), 111 to 107 (C6H5PH ± 2H), 94 (C6H6O), 78 to 7 (C6H6, C6H5), 65 (H3PO2, C5H5), 51 (C4H3), 47 (PO) and 39 (C3H3) amu. The phenylphosphine is apparently formed by rearrangement in the excited state after electron‐impact rather than by thermal disproportionation in the sample as the latter requires the formation of relatively more of the phosphonic acid than is observed. At higher sample temperatures (120°C) somewhat increased amounts of the phosphonic acid, presumably formed by partial disproportionation in the sample, are observed. Accurate mass assignments and broad metastables confirm the postulated fragmentation processes.
Etude de steroides fluores par spectrometrie de masse—III: Spectres de masse de quelques cetones fluorees
Authors: Chavis C. , Fonzes L. , Guida A.
Published: May 2005

Une série de 24 cétones stéroïdes fluorées a été étudiée enspectrométrie de masse. Les différentes positions de la fonction cétone et de l'atome de fluor ont permis de mettre en évidence des fragmentations intéressantes.
Mass spectrometry of aralkyl compounds with a functional group—XII: Unorthodox elimination of hydrogen cyanide from hydrogen randomized molecular ions of benzylcyanide and of o‐, m‐ and p‐cyanobenzylcyanides, revealed by D‐, 13C‐ acid 15N‐labelling
Authors: Molenaar‐Langeveld T. A. , Nibbering N. M. M. , De Boer Th. J.
Published: May 2005

Specific D‐labelling in the side‐chain and in the phenyl ring, 13C‐labelling in the benzylic position and in the cyano group and 15N‐labelling in the cyano group of benzylcyanide show, that the molecular ion, decomposing in the second field free region, i.e. having a low internal energy, loses hydrogen cyanide with participation of both side‐chain carbon atoms (22% benzylic carbon and 78% cyano carbon) after a complete randomization of all hydrogens. This sharply contrasts with the loss of hydrogen cyanide from the hydrogen randomized molecular ion, decomposing in the ion source, where the original cyano group is involved exclusively.

The molecular ions of (o, m, p)‐cyanobenzylcyanides, decomposing in the ion source as well as in the second field free region, also lose hydrogen cyanide, involving to some extent (6 to 15%) a carbon atom, different from that of the side‐chain cyano group, after an extensive randomization of hydrogens as shown by specific D‐labelling in several positions and by 13C‐ and 15N‐labelling in the side‐chain cyano group. Furthermore, the molecule of hydrogen cyanide, eliminated in the ion source and in the second field free region, appears to contain predominantly the side‐chain cyano group (±70%), thus suggesting that few or none of the molecular ions have rearranged to a seven membered ring.
Mass spectrometry of pyridine compounds—II: Hydrogen exchange in the molecular ions of isonicotinic—and nicotinic acid as a function of internal energy
Authors: Neeter R. , Nibbering N. M. M.
Published: May 2005

From the mass spectra of site‐specifically deuterated analogues of isonicotinic acid it appears that the molecular ion eliminates hydroxyl and water after an exchange between the hydroxylic and β‐hydrogens. The percentage of exchange in these reactions depends on the internal energy of the molecular ion and is shown to be 53 to 57% in the ion source, 92 to 97% in the first and ∽ 100% in the second field free regions.

Furthermore, the isotope effect i, operative in the loss of water, increases with decreasing internal energy of the molecular ion, being 1.6, 2.0 and 2.3 in the ion source, first‐ and second field free regions, respectively.

In the molecular ions, losing successively hydroxyl and carbon monoxide as deduced from diffuse peaks in the first‐and second field free regions, a substantially lower percentage of exchange (ca. 20%) is found, which is due to the higher internal energy of these molecular ions.

In the molecular ion of nicotinic acid only one of the ortho hydrogens (α) is involved in the exchange of hydrogen. The percentage of exchange for loss of hydroxyl in the ion source is 66%. Molecular ions, which successively eliminate hydroxyl and carbon monoxide, show a 45% exchange of hydrogen as calculated from diffuse peaks in the first‐ and second field free regions.
A mass spectrometric study of 4‐hydroxy‐6‐methyl‐2‐pyridone and its derivatives
Authors: Wulfson N. S. , Zaikin V. G. , Ziyavidinova Z. S. , Burikov V. M. , Mukerjee S. K.
Published: May 2005

The mass spectra of 4‐hydroxy‐6‐methyl‐2‐pyridone, its N‐methyl and N‐phenyl derivatives, and also their 4‐O‐acetyl and 3‐C‐acyl derivatives have been studied. The proposed fragmentation pathways were supported by comparison of the mass spectra and in some cases by the spectra of deutero analogues. A strong N‐phenyl group effect has been found, which in the case of N‐phenyl‐4‐hydroxy‐ and N‐phenyl‐4‐acetoxy‐6‐methyl‐2‐pyridones promotes the formation of the stable [M—H]+ and [M—CH3CO]+ ions respectively. These ions are not characteristic of the N—H and N—Me analogues.
2‐(1‐Azulyl)ethyl tosylate methylene scrambling in the gas phase. Similarities to solution chemistry
Authors: Graham Cooks R. , McDonald Richard N. , Curtis James R. , Petty Herbert E.
Published: May 2005

The methylene groups in 2‐(1‐azulyl)ethyl tosylate are largely scrambled prior to formation of fragment ions in the mass spectrometer. This process also occurs in the 3‐nitro analog, where it is dependent on sample residence time in the source and independent of electron energy. It could not be observed with the isomeric 6‐substituted tosylates, the 1‐substituted acetates or alcohols, or with 2‐(p‐anisyl)ethyl tosylate. Scrambling occurs in the neutral molecule prior to ionization and a mechanism involving absorption onto the metal surface and formation of a complexed ethylenazulonium ion is suggested.
Potentiel d'ionisation, potentiel d'apparition et courbes d'ionisation differentielle pour les 1‐2 dimethylcyclohexanes CIS et Trans
Authors: Lageot C.
Published: May 2005

Les potentiels d'ionisation et d'apparition de différents ions ont été mesurés pour les deux composés cis et trans 1‐2 diméthylcyclohexanes par la méthode EDD. Les différences notées dans les courbes d'ionisation différentielle des ions [M—CH3]+. et [M—2CH3]+. nous conduisent à admettre une réorganisation donnant naissance à des ions cyclobuteniques.
Potentiel d'ionisation, courbes d'efficacite d'ionisation differentielle, localisation de la charge de 9 cyclopropanes
Authors: Lageot C.
Published: May 2005

Rües potentiels d'ionisation, les courbes d'efficacité d'ionisation différentielle ont été déterminées par la méthode EDD

EDD: Energy Difference Distribution (voir R. E. Winters).6

pour 9 cyano‐1 diphényl‐l,2 cyclopropanes. II est montrk que les composés comprenant le groupement diméthylamino possedent les potentiels d'ionisation les plus bas. Pour ces cornposés, on peut établir une corrélation qualitative entre le potentiel d'ionisation, la première cassure dans la courbe d'efficacité d'ionisation différentielle et la constante de Hammett. Pour les composés comprenant le groupement nitro, la valeur constante de la première cassure au dessus du potentiel d'ionisation nous permet de penser que ce substituant a un rǒe primordial dans l'état excité des ions moléculaires.
Aromatic perchlorocarbons and perchlorocarbon radicals as mass spectral reference standards
Authors: Freeburger Michael E. , Mason Hughes B. , Spialter Neonard , Tiernan Thomas O.
Published: May 2005

The mass spectral cracking patterns of several aromatic perchlorocarbons and perchlorocarbon radicals are reported. These include the first examples of mass spectra of stable carbon free‐radical substrates, and they do not differ significantly from those of structurally similar neutral substrates. All the compounds show successive loss of chlorine atoms with very little fragmentation of the carbon skeleton. This class of compounds has potential value to mass spectroscopists as reference standards in the range m/e 300 to 700.
Studies in organic mass spectrometry—IV: N‐iminopyridinium betaines
Authors: Ikeda M. , Tsujimoto N. , Tamura Y.
Published: May 2005

The mass spectra of N‐iminopyridinium betaines, which have been generated within the ion source by pyrolysis of the corresponding hydrochlorides, have been compared with those of pyridine N‐oxides.
Electron‐impact induced skeletal re‐arrangement of 2‐methoxy‐3‐methylpyrazine and 2‐methylthio‐3‐methylpyrazine
Authors: Kolor Michael G. , Rizzo Donald J.
Published: May 2005

The mass spectra of 2‐methoxy‐3‐methylpyrazine (I), 2‐methoxy‐6‐methylpyrazine (II), 2‐methylthio‐3‐methylpyrazine (III) and 2‐methylthio‐6‐methylpyrazine (IV), are given and the major fragmentation pathways discussed. The novel loss of H2O from the molecular ion of I and the corresponding loss of H2S from the molecular ion of III indicate that a skeletal rearrangement takes place in the molecular ion preceding the expulsion of H2O and H2S. Proposed mechanisms for this behavior are discussed with evidence being drawn from accurate mass measurement, metastable ions, and deuterium and carbon‐13 labeling of the methoxy group. The absence of ions in the spectra of II and IV corresponding to the loss of H2O and H2S from these molecular ions clearly indicates that the position of the methyl group with respect to the methoxy group, or the methylthio group is in‐timately involved in this mechanism.
Heterocyclic studies—XXIV: Mass spectra of some pteridin‐4(3H)‐ones and 3‐methoxypteridin‐4(3H)‐ones
Authors: Clark Jim , Maynard Ruth , Smith C.
Published: May 2005

Mass spectra of pteridin‐4(3H)‐one and all its mono‐, di‐ and tri‐C‐methyl derivatives are recorded. Spectra of 3‐methoxypteridin‐4(3H)‐one and four of its mono‐ and dimethyl derivatives are also recorded.

Pteridin‐4(3H)‐one fragments mainly by loss of CO and HCN in either order. Methyl substitution in the pyrazine ring leads to that ring fragmenting in preference to the oxygen bearing pyrimidine ring. Elucidation of fragmentation pathways was facilitated by changes in peak positions with changing methyl substitution patterns.

3‐Methoxypteridin‐4(3H)‐ones fragment mainly through initial loss of CH2O, but the ions so produced break down differently from isomeric molecular ions of pteridin‐4(3H)‐ones. Several fragmentation pathways are discussed.
Rearrangement and cyclization reactions in the mass spectra of a series of isatin carbonyl derivatives of medicinal interest: 2‐Oxo‐3‐indolinylidene anils (n‐arylketimines), 2‐oxo‐3‐indolinylidene phenylhydrazones, 2‐oxo‐3,3‐bis‐(o‐diaminoaryl) indolyl deriv‐atives and their 2,3‐quinoxaline heterocyclic analogues
Authors: Ballantine J. A. , Fenwick R. G. , Popp Frank D.
Published: May 2005

The mass spectra of several types of carbonyl derivatives of isatin have been examined and the fragmentation pathways have been studied. There are many differences from previously reported data on similar derivatives of less complex carbonyl compounds and several rearrangement processes have been shown to be involved in the cleavage reactions. Some interesting examples of ‘ortho‐effects’ have also come to light as a result of this investigation.
Spectrometrie de masse de biphenyles 0,0'–pontes—II
Authors: Maquestiau A. , Van Haverbeke Y. , Delalieu F.
Published: May 2005

L'étude par spectrométrie de masse de trois types de biphényles montre que ces produits se dégradent de façon similaire. Néanmoins, des variations d'intensité suggèrent que la nature du pont influence les cinétiques de plusieurs mécanismes en cascade.
Über eine einfache methode zur formierung von Rhenium‐Kathoden
Authors: Müller J.
Published: May 2005

Durch Einwirkung flüchtiger metallorganischer Thorium‐Verbindungen, z.B. Th(C5H5)4, auf Rhenium‐Kathoden werden deren Emissionseigenschaften wesentlich verbessert. Es kann bei reduziertem Kathodenheizstrom und dadurch bei tieferen Ionenquellentemperaturen gearbeitet werden. Der Effekt hält über mehrere Wochen oder Monate an.
The mass spectrometry of phenothiazines—I. 10‐alkylphenothiazines
Authors: Simov D. , Taulov I. G.
Published: May 2005

The fragmentation of six substituted 10‐alkylphenothiazines is discussed. Predominant expulsion of OH, SO and O occurs from the molecular ions of 10‐alkylphenothiazine‐5‐oxide derivatives, the relative extent depending upon the configuration of the 10‐substituent. The simultaneous elimination of two OH radicals from the molecular ion of 10‐alkylphenothiazine‐5‐sulphone derivative is also observed.
Oligosaccharide sequencing by means of mass spectrometry‐II: Acetates of N‐arylglycosylamines
Authors: Chizhov O. S. , Kochetkov N. K. , Malysheva N. N. , Shiyonok A. I. , Chashchin V. L.
Published: May 2005

The fragmentation of the N‐arylglycosylamines of some di‐, tri‐ and tetrasaccharides under electron‐impact has been studied. The results indicate that these derivatives can be used successfully for the determination by mass spectrometry of the molecular weight, sequence of monosaccharide units and, in some cases, for the elucidation of the positions of glycosidic linkages.
Studies in organic mass spectrometry—IX: The fragmentation of alkylsubstituted 1,3‐cyclopentanediones
Authors: Cant E. , Vandewalle M.
Published: May 2005

The mass spectra of 2‐ and 4‐substituted 1,3‐cyclopentanediones are discussed. Methyl substituted compounds display mostly ring degradation, while for longer alkyl groups fragmentations in the side chain are responsible for most of the total ionization. As was found for other 1,3‐diketones the spectra of 1,3‐cyclopentanediones show typical and separate fragmentations for both diketoand enol‐molecular ions.
The mass spectral fragmentation of 2‐aryl‐N, N′‐dimethyl‐1,3‐imidazolidines and 2‐aryl‐1‐3‐dioxolanes
Authors: Horodniak J. W. , Wright J. , Indictor N.
Published: May 2005

2‐Aryl‐N,N'‐dimethyl‐1,3‐imidazolidines and 2‐aryl‐1,3‐dioxolanes were subjected to 70 eV spectral analysis. Fragmentation pathways for both series of compounds are suggested. Aryl vs. benzylic hydrogen fragmentations were subjected to Hammett σ+  ρ plots. Incipient charge on the benzyl carbonium ion was stabilized by electron donating groups in both series of compounds. Dioxolanes were more sensitive to substituent effects (ρ = −0.639) than the imidazolidines (ρ = −0.251) implying that the positive charge on the fragmenting ion is more localized at the benzylic position of the imidazolidines than of the dioxolanes.
A mechanism of mass spectral ketene elimination from phenyl acetates
Authors: Nakata Hisao , Tatematsu Akira
Published: May 2005

Deuterium labelling experiments show that mass spectal ketene elimination from O‐acetyl methyl salicylate involves a four‐membered cyclic transition state and gives a phenolic fragment ion.
Studies in mass spectrometry—XVI. The striking difference between the mass spectra of stereoisomeric cyclic anhydrides
Authors: Karpati Annie , Mandelbaum Asher
Published: May 2005

Elimination of CO gives rise to prominent peaks in the mass spectra of cis‐1,2,3,6‐tetrahydrophthalic anhydride (Ia) and its 4,5‐dimethyl analogue which are almost absent in the corresponding trans‐isomers. The striking difference in the fragmentation of the isomers shows that practically no rearrangement in the molecular ion occurs prior to this fragmentation. In this case a high degree of stereospecificity is observed, although hydrogen migration is apparently not involved in the process.
Mass spectra of steroidal alkyl ethers—I
Authors: Narayanan C. R. , Lala A. K.
Published: May 2005

The mass spectral fragmentation of saturated and unsaturated steroidal methyl and ethyl ethers and ethers of 4,4‐dimethyl steroids are studied and compared to the fragmentation of steroidal alcohols, trimethylsilyl ethers and ethylene ketals. Unlike the trimethylsilyl ether the small fragment containing the alkoxy group is neither the base peak nor a very strong peak in the spectrum. A significant peak occurs at [M — ROH]+·, however, sometimes even constituting the base peak of the spectrum. The fragmentations of the alkyl ethers are largely dependent on their environments. The present results also show the generalization that methyl ethers are better leaving groups than the corresponding alcohols in fragmentation processes, is not always valid.
The mass spectra of some O‐methyloximes of aliphatic aldehydes and ketones
Authors: Middleditch B. S. , Knights B. A.
Published: May 2005

The mass spectra of O‐methyloximes of fifteen aliphatic aldehydes and ketones of various molecular weights and degrees of branching have been examined. All give molecular ions, and many of the fragmentations parallel those of aldoximes and ketoximes. The formation of some ions is better explained by the initial production of a novel substituted cyclopropene ion. O‐Methyloximes of of the long‐chain aldehydes and methyl ketones are readily distinguished by the masses of abundant products of McLafferty rearrangement at m/e 73 and 87, repectively.
Formation of benzoyl ions: A complicated simple cleavage reaction
Authors: Turk Jonathan , Shapiro Robert H.
Published: May 2005

Charge exchange and electron‐impact induced cleavages of some N‐phenyl benzamides, phenyl benzoates and benzophenones are reported. The data obtained appear to be consistent with energy being lost from ions by photon emission or stored in isolated states of the molecular ions.
The electron‐impact promoted fragmentation of aurone epoxides
Authors: Brady B. A. , O'Sullivan W. I. , Duffield A. M.
Published: May 2005

The mass spectra of six aurone epoxides have been rationalized with the aid of high resolution mass spectrometry and metastable ion evidence. These compounds fragment in a well defined manner and mechanisms are proposed for the formation of their characteristic ions. Some similarity was observed between the mass spectra of 6‐methoxyaurone epoxide (II), 4‐hydroxy‐7‐methoxy‐3‐phenylcoumarin (VII) and 7‐methoxyflavonol (IX). The possibility that VII and IX are intermediates in the fragmentation of epoxide II is discussed. Thermal rearrangement of aurone epoxide II was shown to yield the corresponding flavonol IX and coumarin VII.
Mass spectrometry of onium compounds—X: on the evaporation of pyridinium‐3‐oxides ionization potential measurements
Authors: Grønneberg Truls , Undheim Kjell
Published: May 2005

Ionization potentials of a number of substituted pyridines have been measured. The ionization potential is dependent on the substituent properties. Derivatives of pyridinium‐3‐oxide are unusual in that they have considerably lower IP values than isomeric covalent structures.
Charge localization: The ion kinetic energy spectra of pyrazine, pyrimidine and pyridazine
Authors: Beynon J. H. , Caprioli R. M. , Ast T.
Published: May 2005

The ion kinetic energy (IKE) spectra of pyrazine, pyrimidine, pyridazine, pyrazine‐d4, pyrimidine‐d4 and pyridazine‐d4 have shown that these compounds can more readily be distinguished on the basis of IKE spectra than mass spectra. Studies of the fragmentation of various doublycharged ions have given information about the localization of charge on the heteroatoms and on the structures of the ions themselves. Transition states from which fragmentation occurs for doublycharged ions with loss of either [H]+ or [D]+ have shown large differences of the order 1 Å between the intercharge distances in the two cases.
The mass spectra of 3‐substituted furans
Authors: Baarschers W. H.
Published: May 2005

A fragmentation pattern characteristic of 3‐substituted furans, in which the 3‐substituent carries an oxygen function, is discussed. Examination of the spectra of some meliacins, as well as those of some synthetic model compounds, illustrates the diagnostic value of this particular fragmentation. In addition the spectrum of methyl limonilate (III, R = CH3) is discussed in some detail.
Mass spectrometry in structural and stereochemical problems—CCXVI: Anomalous cleavage ions in bifunctional compounds resulting from participative interaction
Authors: Dias Jerry Ray , Djerassi Carl
Published: May 2005

Two types of remote group interaction after electron‐impact are possible: one involving the transfer of an atom or group of atoms and the other involving expulsion of a group of atoms concomitant with ring closure. These interactions were examined in a homologous series of polyfunctional compounds at high and low ionizing voltages. Fragmentation resulting from remote group interaction in hydroxy ethyleneketals occurs exclusively via 5‐, 6‐ and 7‐membered rings. This is contrasted with the remote group interaction of keto esters, diesters and other literature examples in which ring size (e.g. 5‐15‐membered) plays no significant role.
Electron‐impact studies—LXX. Substituent effects in the negative‐ion spectra of nitroaryl esters
Authors: Bowie J. H. , Nussey B.
Published: May 2005

The negative‐ion mass spectra of a variety of substituted nitroaryl benzoates and aryl nitrobenzoates have been studied. Pronounced proximity effects are observed in the spectra of ortho‐substituted compounds. The meta and para pairs fragment in a similar manner. Linear plots are observed for many cleavages using either the McLafferty or Harrison methods. Evidence is provided which suggests that the fragmentations of meta and para isomers may proceed by the same mechanistic pathway. The magnitude of ρ does not appear to provide precise information concerning the nature of the transition state for a particular reaction of a negative ion.
Mechanism of the elimination reactions in α,δ diols and their halogenated derivatives under electron‐impact
Authors: Horváth Gy. , Kuszmann J.
Published: May 2005

Mass spectrometric investigations of α,δ diols and their halogenated derivatives revealed the necessity of postulating a mechanism for both their elimination of water and of haloid acid. This mechanism proceeding via a transition state of larger ring‐size than described for similar monofunctional aliphatic compounds was confirmed by deuterium labelling.
Ring H/hydroxyl H scrambling before loss of water from salicylic acid molecular ions
Authors: Benezra Steven A. , Bursey Maurice M.
Published: May 2005

Scrambling before formation of the [M — 18] ion from salicylic acid is considerably reduced in comparison with scrambling before formation of the [M — 17] ion from benzoic acid.
A labeling study of π‐cycloheptatrienetricarbonylchromium(0)
Authors: Tibbetts Fred E. , Bursey Maurice M. , Little William F. , Willeford Bennett R. , Benezra Steven A. , Hoffman Michael K. , Jennings Paul W.
Published: May 2005

Peaks of different intensities in the mass spectra of π‐toluenetricarbonylchromium and π‐cycloheptatrienetricarbonylchromium were studied by deuterium labeling of the latter compound. Incomplete hydrogen randomization in cycloheptatriene ligands preceding different reactions was observed, in contrast to the results for cycloheptatriene itself.
The mass spectra of carboxylic acids—V: Carboxyl‐carboxyl interaction in the fragmentation of some cycloalkene‐1,2‐dicarboxylic acids
Authors: Benoit F. , Holmes J. L.
Published: May 2005

The fragmentation mechanisms of the six isomeric cyclohexene‐1,2‐dicarboxylic acids are discussed. Only the 1‐cyclohexene acid, by virtue of the major sequential losses of H2O and CO2 from the molecular ion, is readily distinguishable from its isomers, all of whose mass spectra are closely similar. In contrast to cis and trans cyclohexane‐1,2‐dicarboxylic acids, whose mass spectra were markedly different, the cis and trans cyclohexene‐1,2‐dicarboxylic acids fragment in a similar fashion. The mass spectra of 1‐cyclopentene‐1,2‐dicarboxylic acid and 1‐cyclobutene‐1,2‐dicarboxylic acid also exhibit a strong carboxyl‐carboxyl interaction; the fragmentation behaviour of the 1‐cyclopenteneacid is, however, more complex than that of the 1‐cyclohexene and 1‐cyclobutene acids.
Spectrometrie de Masse des Acetates de la Serie Bicyclo‐(2.2.1) heptane. Elimination de Cetene et Fragmentation Type
Authors: Kossanyi J. , Furth B. , Morizur J. P.
Published: May 2005

L'élimination de cétène à partir acéates de la série bicyclo [2.2.1] heptane se produit par un mécanisme à quatre centres qui conduit à l'alcool correspondant. Une fragmentation type, apparentée aux réarrangements connus pour les carbocations del al série, est mise en évidence lorsqu'il y a une insaturation exocyclique en 3.
Mass spectra of some sulphonyl azides
Authors: Campbell M. M. , Dunn A. D.
Published: May 2005

A series of sulphonyl azides decomposed upon electron‐impact with loss of azide radical. This fragmentation was in marked contrast to the photochemical behaviour of the compounds. An interesting ortho‐extrusion process occurred in the mass spectrum of 2,4,6‐triisopropylbenzenesulphonyl azide.
The mass spectra of styryl sulfoxides and sulfones
Authors: Kinstle Thomas H. , Oliver William R.
Published: May 2005

A variety of rearrangement reactions have been documented in the gas phase ion chemistry of styryl sulfoxides and sulfones. The styryl group rearranges from sulfur to oxygen as evidenced by loss of SCH3 from methyl styryl sulfoxide and loss of SOCH3 from the corresponding sulfone. The resulting m/e 119 ion loses carbon monoxide in one fragmentation route and alternatively loses a hydrogen atom from the aromatic nucleus to produce the benzofuran molecule ion via an electrophilic aromatic ring closure reaction. Styryl sulfoxides lose both carbon monoxide and formyl radicals directly from their molecule ions, but the corresponding sulfones do not fragment in this manner. The mechanisms of the above reactions, as well as others, were investigated using substituent and deuterium labeling. The styryl group has been shown to migrate in preference to a phenyl or substituted phenyl group by investigation of the mass spectra of appropriate aryl styryl sulfoxides and sulfones.