bluuebunny/crossref_metadata_2025 huggingface dataset:
The mechanism of formation of [C4H9O]+ ions from isobutyl ethyl ether
Authors: Audier H. E. , Bouchoux G. , Hoppilliard Y. , Milliet A.
Published: May 2005

It is demonstrated by means of metastable ions characteristics, collisional activation, deuterium labelling and appearance energy measurements that ionized ethyl isobutyl ether and ethyl n‐butyl ether isomerize prior to decomposition. The lower critical energy fragmentation gives [CH3CH2OCHCH3]+ ions. A mechanism of isomerization is proposed in which 1,4 hydrogen migration on the oxygen atom is coupled with rearrangement of the butyl chain.
Derivatization and mass spectrometric investigations of substituted benzeneboronic acids. The use of linked scanning during gas chromatography mass spectrometry
Authors: Longstaff Colin , Rose Malcolm Edward
Published: May 2005

Substituted benzeneboronic acids are important intermediates in the synthesis of support matrices for affinity chromatography but their analysis by mass spectrometry is hindered by thermal reactions in the ion source. A simple derivatization with 1,2‐ or 1,3‐diols removes this difficulty and imparts sufficient volatility for application of gas chromatography/mass spectrometry. The mass spectra of the resulting boronate esters are discussed with reference to high resolution measurements, isotope labelling studies and observation of metastable ions. ortho Substituents are shown to interact strongly during fragmentation. Linked scanning at constant B/E was used to characterize fragmentation pathways and the compatibility of linked scanning and GC/MS is reported.
Mass spectra of chlorinated esters: 2—Methyl mono‐ and dichlorobutanoates
Authors: Korhonen Ilpo O. O.
Published: May 2005

The mass spectral fragmentations of methyl mono‐ and dichlorobutanates have been studied. Deutrium labelling and metastable ion analysis were used to elucidate the fragmentation mechanisms. The molecular ion peaks of the esters are weak and show only in the spectra of the monochloro isomers. A McLafferty rearrangement gives the base peaks in the spectra of methyl 2‐chloro‐, 4‐chloro‐ and 4,4‐dichlorobutanoate; α‐cleavage, [COOCH3]+, in methyl 2,2‐ and 2,4‐dichlorobutanoate; [MCl]+, in methyl 3‐chlorobutanoate; [MClHCl]+, in methyl 3,4‐dichlorobutanoate; [MClCH2CO]+, in methyl 3,3‐dichlorobutanoate and [MClCOOCH3]+˙, in methyl erythro‐ and threo‐2,3‐dichlorobutanoate. The mass spectra of the stereoisomers are nearly identical, the loss of a chlorine atom and the McLafferty rearrangement giving the higher peaks in the spectrum of the threo form.
Cyclic organophosphorus compounds: XVII—the mass spectra of some 5,5‐dimethyl‐perhydro‐1,3,2‐oxazaphosph(v)orines
Authors: Edmundson R. S.
Published: May 2005

The electron impact mass spectra of six 5,5‐dimethyl and eleven 3,5,5‐trimethyl‐perhydro‐1,3,2‐oxazaphosphorine 2‐oxides and 2‐sulphides are reported and compared with those of analogous 5,5‐dimethyl‐1,3,2‐dioxaphosph(v) orinans. Compounds of the 3,5,5‐trimethyl series produce an important ion at m/z 44 which clearly distinguishes them from the 5,5‐dimethyl series. The 2‐sulphides are characterized by loss of thiol radical rather than of sulphur; in the case of 2‐cyclohexylamino‐3,5,5‐trimethyl‐perhydro‐1,3,2‐oxazaphosphorine 2‐sulphide at least, the thiol hydrogen is derived from the oxazaphosphorine ring NCH2 group. Fission of the oxazaphosphorine ring occurs largely, but apparently not exclusively, at the POC linkages.
Gas chromatographic mass spectrometric indication of double bond position in monounsaturated primary acetates and alcohols without derivatization
Authors: Leonhardt B. A. , DeVilbiss E. D. , Klun J. A.
Published: May 2005

Electron impact mass spectra of straight chain, monounsaturated C12 to C18 acetates and alcohols have been shown to be useful in the indication of the double bond position on an empirical basis. The ratio of intensities of the m/z 55 and m/z 54 ions increases proportionately as the double bond is moved away from the acetate or alcohol functional group. The intensity of the m/z 61 ion also can be correlated with the double bond position. Results are generally accurate to ±1 carbon atom.
The methylamine radical cation [CH3NH2]+˙ and its stable isomer the methylenammonium radical cation [CH2NH3]+˙
Authors: Bouma Willem J. , Dawes Judith M. , Radom Leo
Published: May 2005

The potential energy surface for the [CH5N]+˙ system has been investigated using ab initio molecular orbital calculations with large, polarization basis sets and incorporating valence‐electron correlation. Two [CH5N]+˙ isomers can be distinguished: the well known methylamine radical cation, [CH3NH2]+˙, and the less familiar methylenammonium radical cation, [CH2NH3]+˙. The latter is calculated to lie 8 kJ mol−1 lower in energy. A substantial barrier (176 kJ mol−1) is predicted for rearrangement of [CH2NH3]+˙ to [CH3NH2]+˙. In addition, a large barrier (202 kJ mol−1) is found for loss of a hydrogen radical from [CH2NH3]+˙ via direct N—H bond cleavage to give the aminomethyl cation [CH2NH2]+. These results are consistent with the existence of the methylenammonium ion [CH2NH3]+˙ as a stable observable species. The barrier to loss of a hydrogen radical from [CH3NH2]+˙ is calculated to be 140 kJ mol−1.
Fast atom bombardment mass spectrometry of salts
Authors: Javanaud C. , Eagles J.
Published: May 2005

The positive and negative fast atom bombrdment spectra of two groups of simple salts have been recorded. The structures of the major ionic species of eight chlorides and five, complex anion, sodium salts have been interpreted and tabulated.
Effect of overcrowding in mass spectra for six violanthrenes
Authors: Ueda Toyotoshi , Ohno Mitsuru , Harada Hisashi , Iwashima Satoshi , Aoki Junji , Kan Teruo
Published: May 2005

The mass spectra of six highly purified violanthrene samples of class A—(benzo[rst]anthro[10,1,2‐cde]pentaphen, benzo[rst]phenanthro[10,1,2‐cde]pentaphene), class B—(benzo[rst]phenanthro[1,10,9‐cde]pentaphene, dibenzo[a,rst]naphtho[8,1,2‐cde]pentaphene) and class T—(tetrabenzo[a,cd,j,lm]perylene, tetrabenzo[de,hi,op,st]pentacene) were measured. The dependence of relative ion instensities for monovalent, divalent and trivalent ions [M]i+, [M – 2n]i+ and [M – 15]i+ (i = 1, 2, 3) showed clearly the effect of overcrowding in condensed aromatic rings, i.e. the number of H2 molecules which are readily eliminated from the molecular ions is zero for class A, one for class B, and two for class T. These numbers are the same as the number of overcrowded hydrogen atom pairs for each class.
Pyrolysis reaction of carpronium chloride and its structurally related compounds. 2—a mass spectrometric study of the lactonization mechanism
Authors: Ohya Kazumi , Kitaoka Hiroaki , Yotsui Yasuhiko , Sano Mitsuji
Published: May 2005

The mechanism of the pyrolysis reaction of carpronium chloride [(CH3)3N+(CH2)3COOCH3CI−] leading to γ‐butyrolactone and tetramethylammonium chloride was investigated by means of thermal analysis, pyrolysis gas chromatography mass spectrometry and field desorption mass spectrometry, using deuterium labelling. The results indicated that carpronium chloride pyrolysed to yield equimolar amounts of γ‐butyrolactone and tetramethylammonium chloride, methyl transfer occurred between N and O during the pyrolysis process. The mechanism is discussed on the basis of the experimental results, and with the aid of the theoretical results calculated by the CNDO/2 method. The mechanism presented is as follows. γ‐Butyrolactone is formed by the intramolecular migration of the π‐orbital of CO to the carbon adjacent to [(CH3)3N]+ via a 5‐membered ring transition state, accompanied by a bimolecular reaction between [(CH3)3N]+ and the CH3 of OCH3, resulting in the formation of tetramethylammonium chloride in an amount equimolar with γ‐butyrolactone.
An electron impact study of HCN elimination from indolizine by use of 13C labelling
Authors: Corval Madeleine , Lautié Marie‐France
Published: May 2005

The study of the loss of HCN from the molecular ions of [1‐13C]‐, [2‐13C]‐ and [3‐13C]‐indolizine shows that, if the C‐3 atom is eliminated predominantly, as may be expected, the C‐2 atom, and (a) carbon atom(s) of the hexagonal ring are also involved. The losses of 13CCH3. and C2H3. from the [MH12CN]+˙ ions of the three compounds point to the interference of distinct mechanisms of HCN elimination, leading to different structures for the [C7H6]+˙ ions.
The electron impact mass spectra of some rotenoid derivatives
Authors: Kostova I. , Ognyanov I. , Budzikiewicz H.
Published: May 2005

The fragmentation behaviour of several rotenoids functionalized in the alicyclic portions of the molecule is described.
Collisionally activated dissociation of field desorbed protonated dinucleoside phosphates
Authors: Linscheid M. , Burlingame A. L.
Published: May 2005

The collisionally activated dissociation (CAD) of six protonated dinucleoside monophosphates produced by field desorption has been studied by linked scanning (B/E=constant). Complete spectra with detailed structure information have been obtained despite the small ion currents and other technical problems. It is possible to distinguish isomeric sequences in both ribo‐ and deoxyribo‐nucleotides series.
Mass spectral analysis of schiff bases derived from 1,1,1‐trifluoro‐2,4‐pentanedione and 1,2‐diaminoethane, 1,3‐diaminopropane, 1,4‐diaminobutane and 1,2‐diaminobenzene and their copper(II) and nickel(II) complexes
Authors: Morris M. L. , Koob R. D.
Published: May 2005

The mass spectra of the title compounds have been determined and special attention has been given to metastable transitions and ion composition assignments. The interpretation of the mass spectra of N,N'‐ethylenebis(5,5,5‐trifluoro‐4‐oxopentan‐2‐imine) and its metal complexes is relatively straightforward. Bond breaking α and β (with H transfers) to nitrogen in the ethylenediamine portion of the molecule overwhemingly dominates the spectra. Changing the diamine bridge adds new features to the spectra in both expected and unexpected ways. Ligand fragmentation changes little when complexed to nickel as compared to hydrogen. Chelation of Cu(II) on the other hand leads to new fragmentation channels which increase in importance as electron availability in the diamine bridge increases. These new reactions are attributed to a reduction of the copper centre in the molecule.
Electron impact induced water elimination from hydroxyamides. 1—N‐(2′‐hydroxyethyl)piperidone‐2 and N‐3′‐hydroxypropyl piperidone‐2
Authors: Steiner B. , Schumann D. , Hoffmann H.
Published: May 2005

The main process of the electron impact induced water elimination of the title compounds takes a reaction course comprising several individual steps. A characteristic neighbouring group participation of the carbonyl function is involved, onto which a hydrogen is transferred in a first rate‐determining reaction step. This rearranged hydrogen is finally lost together with the hydroxyl group. The reaction of N‐(2′‐hydroxyethyl)piperidone follows what seems to be a [1,1] elimination whereas the H2O elimination from N‐(3′‐hydroxypropyl)piperidone represents a formal [1,2] elimination.
Internal energy and angular momentum effects on collision induced dissociation fragmentation patterns
Authors: Jarrold M. F. , Illies A. J. , Kirchner N. J. , Bowers M. T.
Published: May 2005

Data are reported on the effects of internal energy and angular momentum on the collision induced dissociation CID fragmentation pattern. For the ions studied changes in the relative intensities of the fragment ions as internal energy varied were found to be larger than suggested by McLafferty and coworkers. Possible effects of angular momentum on the CID fragmentation pattern are discussed. The charge stripping spectra of the ions studied were found to be strongly dependent on initial energy and/or angular momentum. Hence care must be taken if charge stripping spectra are used to distinguish ion structures.
Intramolecular single and double hydrogen migrations in the mass spectra of substituted tetrahydro‐1,3,2‐oxazaphosphorin‐2‐oxides
Authors: Kulkarni P. S. , Gogte V. N. , Modak A. S. , Sahasrabudhe S. D. , Tilak B. D.
Published: May 2005

The mass spectral fragmentation of substituted tetrahydro‐1,3,2‐oxazaphosphorin‐2‐oxides occurs by the cleavage of ring bonds. The ions due to simple cleavage, single and double hydrogen migration, seem to be triggered by CO bond cleavage of the oxazaphosphorin ring. The variations in the relative abundance of ions arising due to similar fragmentation modes have been found to depend on the nature of the substituent and the stability of the particular fragment. The single hydrogen transfer process is supported by metastable ion and shift techniques.
Isomeric [C3H4]+· ions: Their identification and generation in dissociative ionizations
Authors: Mommers A. A. , Burgers P. C. , Holmes J. L. , Terlouw J. K.
Published: May 2005

The collisional activation (CA) and charge stripping (CS) mass spectra of the three [C3H4]+· isomers, allene, propyne and cyclopropene, are reported. The extent of isomerization among these ions prior to collisional excitation depends on their internal energy content, but is small. Each [C3H4]+· ion structure also can uniquely be generated via appropriate dissociative ionizations. Analysis of mixtures of [C3H4]+· (daughter) ion structures is, in general, not possible from CA and CS mass spectra alone but may be aided by appearance energy measurements.
The cleavage of a CC double bond after chemical ionization with NO+A complex rearrangement process1
Authors: Bukovits G. J. , Budzikiewicz H.
Published: May 2005

The fragmentation of alkenes after chemical ionization with NO+, involving cleavage of the double bond, has been elucidated by deuterium labelling.
Mass spectra of halogenated esters 5—Chloromethyl esters of aliphatic C2C12n‐carboxylic acids and their monochlorinated derivatives
Authors: Korhonen Ilpo O. O.
Published: May 2005

A study has been made of the mass spectral fragmentation upon electron impact of aliphatic C2C12 chloromethyl esters and all their 66 monochlorinated derivatives. The fragmentation pathways of the parent chloromethyl esters were elucidated with the aid of the 1st FFR metastable ions. A McLafferty rearrangement gives the base peak in the C6C11 parent esters and in almost all the 4‐chloro and ω‐chloro isomers. The subsequent loss of HCl gives a very characteristic peak of the chloromethyl esters and their (3‐ω)‐chloro derivatives at m/z 72, [C3H4O2]+. The 2‐chloro isomers have the corresponding chlorine‐containing fragment ion at m/z 106/108. The mass spectra of 2‐, 3‐, 4‐, 5‐ and ω‐chloro isomers give the characteristic fragment ions, the mass spectra of the other isomers being very similar.
Mass spectral studies of alkylbenzenesulphonic acids through their S‐benzylisothiouronium salts
Authors: Borthakur Arun , Rao V. S. Bhaskar
Published: May 2005

The mass spectra of alkylbenzenesulphonic acids in the form of their S‐benzylisothiouronium salts have been studied. These S‐benzylisothiouronium salts dissociated into two parent reactant ions: (i) alkylbenzenesulphonic acid and (ii) S‐benzylisothiourea. The characteristic fragmentation patterns of alkylbenzenesulphonic acids (0‐5 substituted alkyls) were studied and compared with those of the parent hydrocarbons. The intensity of the molecular ion peak decreased with the increase in the molecular weight of the sulphonic acids. Desulphonation as well as loss of the alkyl group was observed in all the spectra. Migration of the alkyl group from S to O, followed by degradation, was also observed in all the spectra studied.
Fast atom bombardment mass spectrometry of non‐volatile organometallic compounds. Rhodium, iridium and platinum complexes containing a cumulene ligand
Authors: Sharp Thomas R. , White Mitchell R. , Davis Jon F. , Stang Peter J.
Published: May 2005

Fast atom bombardment (FAB) mass spectrometry has been used to examine a series of rhodium, iridium and platinum organimetallic complexes, in which a cumulene ligand is attached to the metal in either σ‐or π‐bonding fashion. The most intense ion formed in the rhodium and platinum series is the metal‐bis(triphenylphosphine) ion, while the [Ir(P(C6H5)3)2CO]+ ion is most intense for the iridium series. The platinum complexes show the most intense molecular ion peaks (up to 35% relative intensity), while the rhodium complexes show the least intense molecular ion peaks. The primary fragmentations of all these complexes occur at the metal‐ligand bonds. The cumulenic ligand is lost as an impact unit in all cases. The FAB mass spectra of Rh(P(C6H5)3)3Cl (Wilkinson's catalyst), Ir(P(C6H5)3)2COCl (Vaska's compound), Rh(P(C6H5)3)2COCl and Pt(P(C6H5)3)2(C2H4)–synthetic precursors or related compounds to the organometallic complexes examined here–are included for comparison.
Mass spectrometry of organic compounds of group V elements 7—N‐alkoxyamines
Authors: Kostyanovsky R. G. , Pleshkova A. P. , Voznesensky V. N. , Rudchenko V. F. , Sh. Trokhova S.
Published: May 2005

The suggestion of participation of the participation Ione electron pair of the nitrogen atom in amine‐type stabilization has been confirmed by a decrease in amine‐type fragmentation and a drastic change in the decomposition routes under electron impact of N‐alkoxyamines.
Fragmentation reactions of some aliphatic esters in the NCl(F−) and NCl(NH2−) mass spectra
Authors: Grützmacher Hans‐Fr. , Grotemeyer Barbara
Published: May 2005

The NCI(F−) and NCI(NH2−) mass spectra of a series of aliphatic acetates and of methyl and ethyl trimethylacetate have been obtained. The formation of fluoroenolate ions CH2COF− and of carboxamide anions RCONH− (R  CH3))CH3C). respectively, is observed besides formation of [M  H]− ions and carboxylate ions RCOO− (R  CH3, (CH3)3C). The relative intensities of the different anions depend on the structure of the ester molecules and on the primary reactant anions. Usually, the NCI(NH2−) spectra of the acetates are dominated by [M  H]− ions ([MD]− ions in the case of trideuteroacetates) fragmenting unimolecularly by elimination of an alcohol. The carboxylate ions are important fragments, too, but carboxamide ions are only observed with large intensities in the NCI(NH2− spectra of the trimethylacetates. The NCI(F−) spectra show much larger intensities of carboxylate ions and fluoroenolate ions. The mechanisms of the fragmentation reactions are discussed. The results indicate that most or even all of the fragment ions in the NCI(F− mass spectra of aliphatic esters are formed by addition‐elimination reactions via a tetrahedral intermediate, while competition between direct proton abstraction and addition‐elimination reactions occurs in the NCI(NH2−) mass spectra because of the higher basicity of NH2− resulting in an early transition state for direct proton abstraction.
A correlation between fragment intensity and critical energy in collisional activation of some ions produced by electron impact
Authors: Bursey Maurice M. , Harvan Donald J. , Ronald Hass J. , Becker Ernest I. , Arison Byron H.
Published: May 2005

A Hammett correlation for ratios of intensities of collision induced fragments of [C4R4]+· ions from tetraphenylcyclopentadienones is predicted on the basis of statistical theory and observed in practice.
Mass spectral fragmentation and rearrangement of isatin derivatives
Authors: Peet Norton P. , Barbuch Robert J.
Published: May 2005

Mass spectral fragmentation pathways were formulated for 1‐alkylisatins, 1‐alkyl‐3‐arylimino‐2‐indolinones and 3‐arylimino‐2‐indolinons bearing no substituent at the 1‐position. Deuterium‐labelled and 13C‐labelled compounds were utilized in this study. An interesting rearrangement of the 1‐alkyl compounds, in which the 1‐alkyl substituent is incorporated into a fulvene ion, was established.
Accurate linked scans based on digital real time mass linearization and function generation
Authors: Friedli Felix
Published: May 2005

A new, commercially available digital linked scan unit mass display/marker is presented operating in real time in a mass range of 0.0 to 1638.3 u without the need for a data system. The prerequisites and limitations of successful linked scans with their consequences for the new design are discussed. Examples give evience of the need for increased accuracy.
Experimental investigation of the molecular ions of the xylenes
Authors: Curtis J. M. , Boyd R. K. , Shushan B. , Morgan T. G. , Beynon J. H.
Published: May 2005

A mass spectrometric method of distinguishing between molecular ions of the three isomeric xylenes (dimethylbenzenes) was sought, in light of recent findigs that photoexcited ions could be distinguished via measurements of kinetic energy release accompanying expulsion of a methyl radical. Provided the molecular ions are formed with low internal energies, reproducible differences were found between relative intensities of collision induced reactions of higher critical energies, than for methyl expulsion. These differences exist both for collision energies in the kilovolt range (double focusing mass spectrometers) and in the range of a few tens of volts (triple quadrupole instrument). Though statistically significant, these differences were small. The mechanism of isomerization and fragmentation was investigated via isotopic labelling studies and measurements of kinetic energy release. Most of the present findings can be rationalized in terms of the most recent version of established mechanisms for reactions of ionized methylbenzenes.
A relation between ion structures and experimental overall cross‐sections for collisionally activated decomposition
Authors: Van Tilborg M. W. E. M. , Van Thuijl J.
Published: May 2005

Collisionally activated dissociation (CAD) mass spectra sometimes appear to be identical in spite of the fact that the precursor ion structures are known to differ. It is shown that determination of the experimental overall cross‐section for collisionally activated decomposition yields valuable extra information. After applying it to examples of known structure, [C4H5N]+·, [C5H5N]+· and [C5H5O]+, it is used to study a more complex problem, that of [C6H6]+· ions from four isomeric precursors.
The behavior of stereoisomeric ions in the gas phase: The Case of cyclohexane‐hexacarboxylic methyl esters
Authors: Audisio Guido , Grassi Maria , Daolio Sergio , Traldi Pietro
Published: May 2005

Not only strong differences in relative abundances of product ions, but also different fragmentation pathways are observed in the electron impact mass spectrosopy of six stereoisomeric cyclohexanehexacarboxylic methyl esters. This unusual behaviour has been studied in detail with the aid of different ionization methyods, B/E and B2/E linked scans, exact mass measurements, deuterium labelling experiments and collisionally activated decomposition spectrometry. A close analogy between the isomerization observed under acidic conditions in condensed phase and that observed under chemical ionization (CH4) conditions is underlined.
Electron impact mass spectrometry of 4, 5‐dihydro‐1,2,4‐benzothiadiazepine‐1,1‐dioxide derivatives
Authors: Vettori Umberto , Lesma Giordano , Nali Micaela , Palmisano Giovanni
Published: May 2005

The fragmentation pathways of some 4,5‐dihydro‐1,2,4‐benzothiadiazepine‐1,1‐dioxide derivatives are discussed on the basis of metastable transition data, exact mass measurements and labelling experiments. These compounds show several primary fragmentation processes: M  SO2, M  OH and one involving an intramolecular oxygen migration (M  CH3NO).
Electron ionization and chemical ionization mass spectra of pyridinium and isoquinolinium ylides
Authors: Bowen D. V. , Skett P. W. , Thorpe J. , Plunkett A. O.
Published: May 2005

Electron ionization (EI) spectra and both positive and negative chemical ionization (CI) spectra have been obtained for four isoquinolinium ylides and two pyridinium ylides. Electron transfer reactions dominate the CI mass specra. The base peak in negative chemical ionization is the [M]−· ion, formed by electron capture. In the positive methane CI spectra the molecular ion, [M]+·, is relatively more intense than [MH]+ showing electron transfer to be the main positive ionization process. In the positive ammonia CI spectra, proton transfer to give [MH]+ is the main ionization process, but electron transfer is also observed. The EI spectra show fragmentations in which the aromatic nitrogen moiety retains the charge and fragmentation is by loss of radicals or small neutral molecules from the side‐chains. Radical driven reactions are proposed to explain these spectra.
Atmospheric pressure ionization mass spectrometry of the polychlorinated dibenzo‐p‐dioxins
Authors: Korfmacher Walter A. , Mitchum Ronald K.
Published: May 2005

The branching ratios for the reaction pathways of 39 polychlorinate dibenzo‐p‐dioxins (PCDDs) under oxygen negative chemical ionization/atmospheric pressure ionization mass spectrometric conditions were measured. These results demonstrated that the PCDDs could be separated into 14 groups by this technique. These results were compared with those reported previously for 14 PCDDs using oxygen negative chemical ionization mass spectrometry.
Translational energy release and stereochemistry of steroids 4—Epimeric 3‐keto and 3‐hydroxy steroids
Authors: Zaretskii Z. V. I. , Dan P. , Kustanovich Z. , Larka E. A. , Herbert C. G. , Beynon J. H. , Djerassi Carl
Published: May 2005

The translational energy, T, released during CH3˙ loss from the molecular ions of epimeric steroid ketones and from both molecular and [M‐H2O]+˙ ions of epimeric alcohols of the androstane, pregnane and cholestane series, differing in the mode of the A/B ring junction, has been measured. These data provide a simple and rapid method for identifying the configuration of the epimeric centres. Of the compounds studied, it is found in 3‐hydroxy steroids that the 5β‐isomers release the smaller amounts of translational energy for CH3˙ loss. In most of the 3‐keto steroids investigated, the opposite is found, i.e. the larger T values are observed for the 5β‐isomers. Exceptions occur when further keto groups are introduced at the 11‐ or 17‐positions. A small range of epimeric pairs of 17‐hydroxy, 17‐keto and 4‐keto steroids have also been studied, the 5β‐isomer giving the lower T value in each case. The importance of hydroxy and keto groups at the various sites within the steroid structure in determining the T values is discussed.
Ortho effect in the fragmentation of 2‐acetoxychalcones under electron impact
Authors: Mentlein Rolf , Vowinkel Erich
Published: May 2005

2‐Acetoxychalcones decompose under electron impact conditions by loss of an acetoxy fragment to form flavylium ions. The effect is restricted to the ortho position and is reduced after hydrogenation of the chalcone double bond. The intense flavylium ion originates—as shown by specific labelling with 18O—from two different fragmentation lines: (a) direct loss of an acetoxy radical by cleavage of the phenolic ArO bond and (b) sequential elimination of ketene and a hydroxy radical.
Ion–molecule reaction in the gas phase 3—nucleophilic substitution of 17ξ‐R‐5α,14β‐androstane‐14,17ξ‐diols under [NH4]+ chemical ionization conditions1
Authors: Tabet J. C. , Bertranne M. , Beloeil J. C. , Stahl D.
Published: May 2005

Under Ammonia chemical Ionization conditions the source decompositions of [M + NH4]+ ions formed from epimeric tertiary steroid alchols 14 OHβ, 17OHα or 17 OHβ substituted at position 17 have been studied. They give rise to formation of [M + NH4H2O]+ dentoed as [MHsH]+, [MsHH2O]+, [MsHNH3]+ and [MsHNH3H2O]+ ions. Stereochemical effects are observed in the ratios [MsHH2O]+/[MsHNH3]+. These effects are significant among metastable ions. In particular, only the [MsH]+ ions produced from trans‐diol isomers lose a water molecule. The favoured loss of water can be accounted for by an SN2 mechanism in which the insertion of NH3 gives [MsH]+ with Walden inversion occurring during the ion‐molecule reaction between [M + NH4]+ + NH3. The SN1 and SNi pathways have been rejected.
Collisionally induced dissociative ionization of neutral products from unimolecular ion fragmentations. 1—Neutral product structures
Authors: Burgers Peter C. , Holmes John L. , Mommers Alexander A. , Szulejko Jan E. , Terlouw Johan K.
Published: May 2005

A method is described for the investigation of the structure of neutral products from the unimolecular (metastable) dissociative ionizations of mass selected ions, by means of the collisionally induced dissociative ionization of the neutral species themselves. The neutral species, with kilovolt translational energies, enter a positively charged collision cell situated in the second field free region of a standard ZAB‐2F mass spectrometer. Dissociative ionization of the neutrals results therein from their collisions with He target gas. The resulting ions are analysed by means of the electric sector and the relative ion abundances are shown to be structure characteristic. For such experiments the neutral flux should be c. ≥ 0.5% of the selected precursor ion flux; the collision gas pressure must be insufficient to cause significant precursor ion fragmentation in the field free region preceding the collision cell. It was shown that HNC is generated in the fragmentation of aniline molecular ions, whereas HCN is the neutral product in the dissociative ionizations of pyridine, benzonitrile and benzyl cyanide. The neutral radical [C, H3, O˙] formed together with [CH3CO]+ from ionized methyl acetate has the structure ˙CH2OH, but that from the analogous fragmentation of the methyl propanoate molecular ion has the structure CH3O˙. Allyl radicals were shown to be generated from [(CH3)2CHCH2OH]+˙ together with [CH3OH2]+ ions.
Matrix effects in the fast atom bombardment protonation of carbohydrates
Authors: Puzo Germain , Prome Jean‐Claude
Published: May 2005

FAB positive mass spectra of trehalose in the presence of different matrices such as glycerol, diethanolamine (DEA) and triethanolamine (TEA) are presented and discussed. Protonated and solvated protonated trehalose ions are observed, of which the relative abundance changes with the liquid matrix used. MIKE spectra of the protonated molecular ions solvated by the matrix show unambiguously that desolvation contributes to the formation of protonated molecular ions. It is shown that the decomposition of these complexes is mainly controlled by the relative proton affinities of the analysed sample and the matrix.
Mechanism of CO loss for protonated 1‐indanone and isomeric [C9H9O]+ ions
Authors: Audier Henri E. , Milliet Arielle
Published: May 2005

In order to establish the mechanism of CO loss occurring during metastable decomposition of protonated 1‐indanone, fragmentations of monocyclic [C9H9O]+ isomers have been studied. These ions of known structure were prepared by CI protonation and fragmentation of the corresponding acids chlorides. It is demonstrated that the wide component of the [MHCO]+ metastable peak induced by protonated 1‐indanone fragmentation is the result of fragmentation of the [C6H5CH2CH2CO]+ isomer ion.
Mass spectrometry of β‐keto aldehydes: Novel hydroxyl transfer reactions
Authors: Kulkarni P. S. , Kamath S. V. , Kamath H. V. , Kulkarni Sheshgiri N.
Published: May 2005

The mass spectral fragmentation of 2,3‐diaryl‐3‐oxo‐1‐propanals has been investigated by low electron energy, metastable defocusing and shift techniques. The o‐nitro group strongly interacts with α‐cleavage reactions of the carbonyl group. The cyclization/elimination processes, accompanied by oxygen and hydroxyl transfer in the mass spectra of o‐nitro‐β‐keto aldehydes, are preceded by hydrogen abstraction by the nitro group.
Chemical ionization mass spectra of alkylphenol and linear alcohol polyethoxylates
Authors: Stephanou Euripides
Published: May 2005

The chemical ionization mass spectra of some tert‐octylphenol ethoxylates and linear alcohol ethoxylates have been determined using methane and ammonia as reactant gases. Proton, [C2H5]+ and [C3H5]+ adducts were observed with attachment on the ring as well as on the oxyethylene chain for the tertiary octylphenol ethoxylates. Proton and [NH4]+ addition reactions were also observed. Alkyl ion and olefin displacement reactions were also important fragmentations. Hydride abstraction and proton, [C2H5]+, [C3H5]+ and [NH4]+ attachment were the most important reactions occurring for the linear alcohol ethoxylates.
Mass spectrometry in structural and stereochemical problems. 2617—The effect of stereochemistry on the course of the characteristic ring D fragmentation of steroid hydrocarbons
Authors: Patterson Donald G. , Haley M. J. , Midgley I. , Djerassi Carl
Published: May 2005

The ring D cleavage of the sterol skeleton with loss of carbon atoms 15, 16 and 17 together with the side‐chain is one of the most characteristic and structurally useful mass spectral features of steroids. It has been tacitly assumed that the hydrogen rearrangements accompanying this process are not sensitive to stereochemical changes. Using deuterium labeling it has now been demonstrated that the stereochemistry at various positions of the nucleus, notably 8, 9 and 14, strongly affects this process. Possible rationalizations for this unexpected observation are presented.
The site of gas phase cation attachment. The protonation, methylation and ethylation of morpholine, thiomorpholine and 1,4‐thioxane
Authors: Burinsky David J. , Campana Joseph E.
Published: May 2005

The attachment of gaseous positive ions ([H]+, [CH3]+ and [C2H5]+) to morpholine, thiomorpholine and 1,4‐thioxane, through chemical ionization, has been studied by collision spectroscopy. The daughter ion spectra of the ion/molecule reaction products were compared to those of model ions, generated by fast‐atom bombardment of corresponding quaternary ammonium salts, in order to determine the preferred site of reaction for the protonation and alkylation of these multifunctional nucleophilic compounds. For novel entities with no model precursors, the site of cation attachment was postulated on the basis of characteristic fragmentations and trends established by the study of other bifunctional heterocycles. The site of protonation followed predicted trends in proton affinity differences for the various heteroatoms (N>S>O), and the alkyl ion reactivities followed differences in electronegativity or nucleophilicity (S>N>O).
Collision energy effects in tanden mass spectrometry as revealed by a proton‐bound dimer ion
Authors: McLuckey S. A.
Published: May 2005

Mass spectra resulting from collision‐induced decomposition of the proton‐bound dimer of iso‐propylamine and sec‐butylamine have been obtained as a function of laboratory collision energy over the range 10‐6000 eV. The ratio of the two principal fragment ions from the dimer ion measured as a function of collision energy is compared with the ratio expected as a function of internal energy as calcualted based on the statistical theory of mass spectra. This comparison indicates that the average energy deposited into the dimer ion upon collision reaches a maximum at a collision energy of ∼70 eV. The average internal energy of the ions at this collision energy is ∼4.3 eV. Other fragment ions which arise from higher energy decompositions are also observed in the spectra at much lower intensities. The relative intensities of these fragments indicate that the probability for large energy transfers are highest at ke V collision energies. These observations are interpreted on the basis of differences in the postcollision internal energy distributions resulting from keV and eV collisions.
Mass spectrometry of aryl‐substituted benzoylcyclopropanes
Authors: Guziec Frank S. , Luzzio Frederick A. , Yu T. J. , Vouros Paul
Published: May 2005

The electron impact and chemical ionization mass spectra of several benzoylcycloprpanes carrying a wide variety of ring substituents were examined. Cleavage of the benzoyl‐cyclopropyl CC bond was a dominant process in the spectra of the compounds. Retention of the positive charge with either the benzoyl or the cyclopropyl moiety was influenced by the electron‐donating properties of the ring substituents. The stereoselectivity of hydrogen abstraction in the elimination of ArH groups was evaluated using deuterium‐labelled analogs.
A mass spectrometric study of the pyrolysis of gibberellic acid
Authors: Greathead Roger J. , Mason Rod S. , Jennings Keith R. , Page Janet A. , Pryce Robert J.
Published: May 2005

The behaviour of gibberellic acid (GA3) under electron impact and chemical ionization conditions has been examined. The tendency of GA3 to undergo pyrolysis by the loss of the elements of water and carbon dioxide has been identified. Two methods of sample introduction can be used to minimize the occurrence of this pyrolysis. Accurate mass measurement allows the composition of the pyrolysis product to be determined and metastable techniques confirm the structure of this product to be epi‐allogibberic acid rather than its isomer allogibberic acid. This result corrects a misconception in the literature and illustrates the advantage of metastable methods compared with accurate mass measurements, for the determination of small structural differences within a molecule.
Electron capture negative ion and positive ion chemical ionization mass spectrometry of polychlorinated phenoxyanisoles
Authors: Campbell Jo‐Anne B. , Griffin Donald A. , Deinzer Max L.
Published: May 2005

Several polychlorinated phenoxyphenols with three to nine chlorine atoms were examined as their methyl ethers by electron capture negative ion and positive ion chemical ionization and electron impact mass spectrometry. In chemical ionization studies methane, hydrogen, nitrogen, helium and argon were used as reagent gases. Selected compounds were also examined with deuteriomethane, ammonia and deuterioammonia as reagent gases. Utilization of chemical ionization spectra in conjuction with electron impact spectra provides substantial structural information about these compounds. Chemical ionization spectra provide information about chlorine atom substitution. The position of phenoxy substitution can be established from electron capture negative ion and positive ion spectra.
Rearrangement reactions in the positive and negative ion mass spectra of clausmarin A
Authors: Madhusudanan K. P. , Shoeb Aboo
Published: May 2005

The positive and negative ion mass spectra of clausmarin A, a naturally occurring tetracyclic coumarin, have been studied. The base peaks in the positive and negative ion spectra correspond to the complementary ions at m/z 143 and m/z 255, respectively, formed by a rearrangement reaction. The fragmentation pathways have been elucidated with the help of exact mass measurements and in situ deuterium labelling.
Collision‐induced dissociation of negative ions in the gas phase: [Aryl S]−, [aryl SO]− and [aryl SO2]−
Authors: Bowie John H. , Stringer Michael B.
Published: May 2005

Collision‐induced dissociation of the ions [ArS]−, [ArSO]− and [ArSO2]− has uncovered a rich and varied ion chemistry. The major fragmentations of [ArS]− are complex and occur without prior ring hydrogen scrambling: for example, [C6H5S]−→[C2HS]− and [HS]−; [p‐CD3C6H4S]−→[C6H4S]−˙, [CD3C4S]− and [C2HS]−. In contrast, all decompositions of [C6H5CH2S]− are preceded by specific benzylic and phenyl hydrogen interchange reactions. [ArSO2]− and [ArSO2]− ions undergo rearrangement, e.g. [C6H5SO]−→[C6H5O]− and [C6H5S]−; [C6H5SO2]−→[C6H5O] −. The ion [C6H5CH2SO]− eliminates water, this decomposition is preceded by benzylic and phenyl hydrogen exchange.
Fast atom bombardment mass spectrometry of salts of substituted methylene bisphosphonic acids and other analogues of pyrophosphoric acid
Authors: Hutchinson David W. , Semple Graeme
Published: May 2005

Fast atom bombardment mass spectra have been obtained of salts of analogues of inorganic pyrophosphoric acid, e.g. substituted methylene bisphonates, and positive ion fast atom bombardment mass spectrometry (FABMS) has proved to be more successful than negative ion FABMS for the analysis of these salts. Owing to the low molecular weight of these analogues, FAMBS of the free acids and the sodium salts does not always give results which are easy to interpret as interference by peaks from the matrix can occur. However, the potassium salts in a 60% glycerol matrix, when bombarded by argon atoms, give good FAB spectra which are relatively free of interfering peaks.
Mass spectroscopy of natural products. 20—Quinazoline carboxylic acids 4—Comparative positive and negative ion mass spectroscopic studies of 3,4‐dihydroquinazolin‐4‐on‐3‐ylalkanoic acids and 3,4‐dihydro‐1,2,3‐benzotriazin‐4‐on‐3‐ylalkanoic acids
Authors: Schmidt Jürgen , Süsse Manfred , Johne Siegfried
Published: May 2005

The mass spectroscopic behaviour of 3,4‐dihydroquinazolin‐4‐on‐3‐ylalkanoic acids and 3,4‐dihydro‐1,2,3‐benzotriazin‐4‐on‐3‐ylalkanoic acids was studied under positive and negative ionization. The differences in fragmentation both between the ionization modes and between the two heterocyclic systems are discussed by using some 15N‐labelled derivatives.
Further correlations between fragment ion intensity and critical energy. Unimolecular covalent bond fragmentation
Authors: Bursey Maurice M. , Harvan Donald J. , Hass J. Ronald , Becker Ernest I. , Arison Byron H.
Published: May 2005

A correlation of fragment ion intensity with critical energy found in the collisional activation spectra of [C4Ph]+˙ ions produced by electron impact can also be found in the unimolecular mass‐analysed ion kinetic energy spectra of these ions. The P(E) functions of the unimolecular and collisionally activated ions should differ not only in width but also in structure and therefore, the hypothesis that P(E) functions do not have an important effect on these correlations is tested successfully.
The unimolecular and collisionally activated decompositions of fluorine‐substituted tetraphenyltetrahedrane ions on the microsecond time‐scale
Authors: Bursey Maurice M. , Harvan Donald J. , Hass J. Ronald
Published: May 2005

Unimolecular and collision‐induced decomposition products of [C4(C6H5)2(C6H4F)2]+˙ generated from four unsymmetrical sources include [C14H10]+˙ and [C14H8F2]+˙ and so provide evidence for a tetrahedral intermediate. Other decompositions show substantial influence of the position of the ρ‐fluorophenyl ring on ion energy distributions. This influence may be related to the reported absence of peaks diagnostic for the tetrahedral intermediate from the spectrum of the equivalent ion from the appropriate 13C‐labeled analog. Alternatively the difference in spectra can be correlated with lifetimes of ions.
Mass spectral study of ring E of taraxasterol and compounds with similar ring substitution
Authors: Lee Hsiu‐Pu Daniel , Eichmeier Larry S. , Piatak David M.
Published: May 2005

The origin of the [M–69]+ and [M–111]+ signals in the mass spectrum of taraxasterol was studied through the use of C(18), (19), (21), (22) and/or (30) deuteriated derivatives. The generality of these signals for ring systems with an exocyclic methylene group and a methyl moiety on an adjacent carbon was verified with 2‐methylmethylenecyclohexane, 1‐methyl‐2‐methylene‐trans‐decalin, 1,10‐dimethyl‐2‐methylene‐trans‐decalin and some of their deuteriated derivatives. The most plausible mechanism for the formation of the [M–69]+ ion appears to involve cleavage of both bonds allylic to the exocyclic methylene group with a 1,3‐hydrogen transfer from the adjacent ring. Genesis of the [M–111]+ ion is more complicated but a five‐membered allylic ion generated from ring D is proposed.
Chemical synthesis inside the collision cell of a MS/MS system: 1—Formation of adduct ions between protonated esters and ammonia
Authors: Schmit J. P. , Dawson P. H. , Beaulieu N.
Published: May 2005

An evaluation of the TAGA 6000 tandem quadrupole MS/MS capabilities for the study of the formation of adduct ions is presented. It is shown that under chemical ionization conditions the protonated molecular ions of esters react with neutral ammonia inside the collision cell of the instrument to yield adduct ions. Under the same reaction conditions the molecular ions obtained under electron impact conditions do not yield any adduct. Although it is not yet clear whether the adduct structure is of the cluster or covalently bonded type, the experimental results argue mainly in favor of the latter. The center‐of‐mass energy range usable for the formation of adduct ions is narrow and an order of magnitude lower than the energy required for collision‐induced dissociation. However, despite the weak parent ion center‐of‐mass energies used, the spectra exhibit fragments characteristic of the adduct ion structures. Finally, by controlling the parent ion center‐of‐mass axial kinetic energy, the number of parent ions and the target thickness, it is possible to measure and control all the usual physicochemical parameters for adduct ion formation.
Mass spectral rearrangements of 3‐arylsulphonyl‐2‐arylthiopropenes and N‐(4′‐arylsulphonyl‐2′‐butynyl)‐N‐(4″‐arylthio‐2″‐butynyl)anilines
Authors: Glaspy P. E. , Hancock R. A. , Thyagarajan B. S.
Published: May 2005

Under electron impact the title compounds undergo skeletal rearrangement in addition to the anticipated modes of cleavage. The 3‐arylsulphonyl‐2‐arylthiopropenes readily eliminate sulphur dioxide. Other modes of fragmentation include rearrangement to a bisaryl sulphide moiety and sulphone‐sulphinate rearrangement. The formation of a bisaryl sulphide ion is analogous to the behaviour of the isomeric trans‐1‐arylsulphonyl‐2‐arylthiopropenes. N‐(4′‐Arylsulphonyl‐2′‐butynyl)‐N‐(4″‐arylthio‐2″‐butynyl) anilines do not undergo any of the skeletal rearrangements mentioned above, but display the concerted loss of the arylsulphonyl and arylthio moieties. Similar eliminations have been observed from the analogous bis‐sulphides and bis‐sulphones.
Analysis of carbohydrates by fast atom bombardment mass spectrometry: 2—Influence of the matrix and the nature of the alkaline cations in the attachment process of an alkaline cation to a disaccharide molecule
Authors: Puzo G. , Promé J. C.
Published: May 2005

The fast atom bombardment (FAB) ionization process of a non‐reducing disaccharide by an attachment reaction with an alkaline cation has been investigated according to the nature of both the matrix (glycerol, diethanolamine, triethanolamine) and the alkaline cation (lithium, sodium, potassium, rubidium, caesium). We have established that one way of forming the cationized disaccharide molecular ions, [disaccharide‐cat]+, is by a desolvation reaction from the cationized solvated disaccharide molecular ions, [disaccharide‐cat‐matrix]+. This process, which has been established by mass‐analysed ion kinetic energy (MIKE) spectral analysis of the solvated species, is shown to be drastically affected by the nature of the involved matrix but only slightly by the alkaline cation. The variations in the relative abundances of the disaccharide cationized molecular ions compared to their solvated clusters in the FAB mass spectra, due to the matrix employed, have been explained according to the unimolecular dissociation of the solvated clusters examined by MIKE analysis. However, the variations in the abundance of the disaccharide cationized molecular ions in relation to the alkaline cation used—a higher sensitivity has been observed for lithium, sodium and potassium alkaline cations—have been explained in terms of the cations available at the target surface for the attachment process to the sugar molecule, and by a ligand exchange reaction between the matrix and the disaccharide.
In‐beam ionization by alkali ion attachment applying a two‐filament ion source
Authors: Schmelzeisen‐Redeker G. , Giessmann U. , Röllgen F. W.
Published: May 2005

A simple ion source was constructed for in‐beam ionization by alkali ion attachment. A wire probe covered with sample was placed near an alkali ion emitter prepared from a mixture of silica gel and alkali halides. The ionization of various thermally labile compounds and of mixtures was investigated. Na+ proved to be the most suitable alkali ion for cationization. For monosaccharides experiments revealed the elimination of water upon ionization by Li+ attachment. The experimental set‐up was also examined for measuring the heat of sublimation of organic solids.