bluuebunny/crossref_metadata_2025 huggingface dataset:
Mass spectral rearrangements of N‐(4′‐arylthio‐2′‐butynyl) N‐(2″‐arylthio‐2″‐propenyl)‐p‐toluidines, N,N‐bis(2′‐arylthio‐2′‐propenyl)‐p‐toluidines and 1,2‐bis(arylthio)acenaphthenes
Authors: Glaspy P. E. , Hancock R. A. , Thyagarajan B. S.
Published: May 2005

Under electron impact the title compounds display, in addition to the sequential loss of the arylthio groups, the elimination of a bisaryl disulphide moiety, but they do not eliminate sulphur. The behaviour of the p‐toluidine derivatives supports the rearrangement pathway proposed earlier for N,N‐bis(4′‐arylthio‐2′‐butynyl)anilines.
Low‐energy, low‐temperature mass spectra: 4—Saturated alkylamines
Authors: Bowen Richard D. , Maccoll Allan
Published: May 2005

Electron impact mass spectra obtained with 12.0 eV ionizing electrons at a source temperature of 350 K are reported for 32 saturated alkylamines. The abundances of molecular ions and primary daughter ions are discussed in energetic terms, and the effects of extending the alkyl chain or methylation of the nitrogen atom are considered. A contrast is found between the spectra of amines and those of the analogous alcohols and ethers.
Stereoelectronic effects on the retro‐Diels‐Alder fragmentation of ionized bicyclo[4.3.0]nona‐3,7‐dienes
Authors: Tureček František , Pancíř Jiří , Stahl Daniel , Gäumann Tino
Published: May 2005

The electron impact and collision‐induced dissociation mass spectra of cis‐ and trans‐annulated bicyclo[4.3.0]nona‐3,7‐dienes differ in their relative abundances of [C5H6]+˙ fragments formed by the retro‐Diels‐Alder decomposition. The formation of [C5H6]+˙ is not preceded by hydrogen migration in the short‐lived and long‐lived molecular ions. The appearance energy of [C5H6]+˙ from both annulation isomers is identical within experimental error: AEcis([C5H6]+˙)=10.56±0.10 eV and AEtrans([C5H6]+˙)=10.54±0.15 eV. The barrier to the retro‐Diels‐Alder fragmentation lies 68–76 kJ mol−1 above the thermo‐chemical threshold corresponding to [C5H6]+˙ + C4H6. Investigation of the two‐dimensional reaction coordinate by the Topological Molecular Orbital treatment shows that the lowest energy path for the retro‐Diels‐Alder reaction involves a two‐step dissociation of the C(5)C(6) and C(1)C(2) bonds in the molecular ion, the latter step overcoming a barrier, calculated as 80 kJ mol−1 above the thermochemical threshold. The stereochemical difference between the geometric isomers is due to stereoelectronic assistance of the π orbitals of the cis‐annulated isomer in the cleavage of the C(5)C(6) bond. Other mechanisms of the retro‐Diels–Alder reaction are discussed.
Hydrogen chemical ionization mass spectrometry of metalloporphyrins
Authors: Evershed Richard P. , Wolff George A. , Shaw Graham J. , Eglinton Geoffrey
Published: May 2005

The hydrogen chemical ionization (H2 CI) mass spectra of a range of metal(II) (Ni, Cu, Co, Pt), metal (III) (Al, Mn, Ga, Fe (bearing a single axial ligand)) and metal(IV) (Si, Ge, Sn (bearing two axial ligands) and V (as VO2+)) porphyrins have been determined, The spectra are highly dependent on the coordinated metal, rather than the axial ligand(s) (where present). Ni(II), Cu(II), Mn(II or III), Ga(III), Ge(IV), Fe(III) and Sn(IV) porphyrins fragment via hydrogenation and demetallation, followed by cleavage of the resulting porphyrinogens at the meso(bridge) positions to give mono‐ and di‐pyrrolic fragments. Tripyrrolic fragments are also observed in the case of Ni(II), Cu(II) and Sn(IV). Fragmentations of this type are similar to those observed for free‐base porphyrins. In the case of Pt(II), Co(II), Al(III), Si(IV) and V(IV) (as vanadyl), the dipyrrolic fragment ions are either very weak or completely absent; hence their H2CI spectra contain limited structural information. This variable CI behaviour may be related to the relative stabilities of the metalloporphyrins together with the multiple stable valency states exhibited by several metals.
Chemical ionization induced competing and consecutive heterolytic ring cleavages 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 chemical ionization mass spectra of some substituted heterocyclic systems, viz. tetrahydro‐1,3,2‐oxazaphosphorin‐2‐oxides, reveal polar cycloreversion reactions. The zwitterion intermediate formed by the heterolysis of the CO bond undergoes stepwise clean heterolysis further resulting in the expulsion of the potential nucleophilic and electrophilic groups. The competitive and consecutive heterolysis of the ring bonds leads to the formation of the protonated phenylimine ions. Competing with heterolysis, elimination reactions involving hydrogen transfer leading to the formation of α‐phenylethyl ions are also observed. The chemical ionization mass spectrometry of the heterocyclic system shows many features of the Grob type of fragmentation mechanism.
The mass spectrometry of 2‐methylthio(glyco)oxazoline derivatives of pentoses and hexoses
Authors: Byrd Gary D. , Davidson Robert M. , Edward White V , Coxon Bruce , Margolis Sam A.
Published: May 2005

The fragmentation of 2‐methylthio(glyco)oxazolines under electron impact has been investigated by low‐ and high‐resolution mass spectrometry. Field desorption was used in those cases where the molecular ion was weak or missing. Fragmentation pathways were determined by monitoring metastable transitions and through the use of labeled compounds. The results support the anticipated structure for these compounds and show the sensitivity of the mass spectra toward ring size.
Ammonium adduct ion in ammonia chemical ionization mass spectrometry: 2—Mechanism of elimination of neutrals from the ammonium adduct ion
Authors: Nakata Hisao , Hoshino Yoshihiko , Takeda Naohito , Tatematsu Akira
Published: May 2005

The mechanism of elimination of ROH (R = H or CH3) from the ammonium adduct ion, [M+NH4]+, of 1‐adamantanol and its methyl ether is examined by using linked‐scan metastable ion spectra and by measuring the dependence of the peak intensity ratio [M+NH4]+/[M+NH4ROH]+ on ammonia pressure. For 1‐adamantanol both SNi and SN1 reactions are suggested in metastable ion decomposition, while only the SN1 mechanism is operative in the ion source. For 1‐adamantanol methyl ether the SN1 reaction predominates both in metastable ion decomposition and in the ion source reaction.
Electron impact fragmentation of some mixed cyclotetraphosphazenes
Authors: Bamgboye T. Tunde , Bamgboye Omolara A.
Published: May 2005

The electron impact fragmentations of some cyclotetraphosphazenes are reported and discussed. The major fragmentation path involves loss of two amine radicals and one chlorine radical in the series P4N4Cl8‐n(NMe2)n when n=2, and subsequent stages involve a ring contraction process with elimination of a P = N fragment, when n = 5 loss of amine radicals predominates on statistical grounds with little evidence of ring contraction. In the series P4N4F8‐n(NMe2)n fragmentation is dominated by loss of amino radicals when n = 4 and loss of fluorine radicals predominates on statistical grounds when n = 2. In the series P4N4F8‐nXn (n = 2 or 4, X = Cl or Br), when n = 2 and X = Br the major fragmentation path is the loss of two bromine radicals, whereas when X = Cl the more favoured path is the loss of two chlorine radicals. In both, subsequent stages involve ring contraction reactions with elimination of a PN fragment. When n = 4 and X = Br or Cl on bond energy grounds the more favoured fragmentation pattern is the loss of bromine or chlorine radicals, respectively.
Characterization of the high molecular mass chlorinated matter in spent bleach liquors (SBL): 3—Mass spectrometric interpretation of aromatic degradation products in SBL
Authors: Österberg F. , Lindström K.
Published: May 2005

The aromatic content of the high molecular matter in pulp mill bleachery effluents has been characterized after chemical degradation in the laboratory followed by derivatization and gas chromatographic/mass spectrometric analysis. Aromatic molecules with carboxy, hydroxy, methoxy and chloro substituents were separated and identified by recording their computer‐reconstructed ion current chromatograms. About 70 aromatic carboxylic acids were tentatively identified as degradation products. Aromatic compounds with hydroxy groups were derivatized to trideuteromethoxy groups in order to distinguish them by mass spectrometry from compounds with naturally occurring methoxy groups. Single and double hydrogen atom transfer between methyl ester and methoxy groups were observed in some molecules and given special attention when they occurred ortho to each other. A methoxy group substituted ortho to a methyl carboxylate resulted in an unusual fragmentation.
Secondary isotope effect on kinetic energy release and reaction symmetry
Authors: Hvistendahl Georg , Uggerud Einar
Published: May 2005

A secondary deuterium isotope effect on the kinetic energy release has been observed for the loss of molecular hydrogen from protonated formaldehyde and protonated methylimine. The results have been used to show that the centre of the reactions lies towards the carbon atom.
Rearrangements in the molecular ion of o‐(methyl‐d3‐thio)benzoic Acid: Comparison with o‐methoxy‐d3‐benzoic acid
Authors: Gillis Richard G. , Porter Quentin N.
Published: May 2005

Hydrogen/deuterium exchange and rearrangements in the molecular ion of o‐(methyl‐d3‐thio)benzoic acid lead to fragment ions [MOD]+ as well as [MOH]+ and m/z 106 and 107, just as in the molecular ion of o‐methoxybenzoic acid. However, the fragment ion m/z 108 has the composition C6H4S rather than C6H2D3CO as it does in the case of o‐methoxy‐d3‐benzoic acid. By varing the repeller potential at 10 eV (and thus the residence time in the ion source), the corresponding fragments are seen to be formed more slowly from the methylthio acid than from the methoxy acid, which leads to the conclusion that H/D exchange between carboxyl and labelled methylthio is slower than it is between carboxyl and labelled methoxyl.
Fragmentation of organic anions induced by exothermic addition reactions
Authors: Depuy Charles H.
Published: May 2005

The addition reactions of a series of carbanions with CO2, COS and CS2 have been studied in a flowing afterglow apparatus. Carbon dioxide simply forms the adduct, but the more highly exothermic additions to COS and CS2 lead both to addition and addition followed by fragmentation. A number of novel fragmentation pathways have been observed for additions to diazo anions and to anions derived by proton abstraction from allenes. In addition to these reactions, highly basic anions are observed to undergo sulfur atom transfer reactions with CS2.
Chemical ionization (NO) spectra of n‐alkenoic acids and their esters
Authors: Brauner A. , Budzikiewicz H. , Francke W.
Published: May 2005

It is shown that the position of one double bond in long‐chain unsaturated fatty acids and their esters can be determined by chemical ionization (NO) mass spectra. Homoconjugated dienoic acids (as linoleic acid) do not give a characteristic framentation pattern, in contrast to those which contain three or more homoconjugated double bonds.
Further studies on a site‐specific hydrogen transfer observed in electron capture negative ion chemical ionization mass spectrometry of hydroxyamine pentafluoropropionate derivatives
Authors: Low G. K.‐C. , Duffield A. M.
Published: May 2005

Further studies have demonstrated that the site‐specific hydrogen transfer process involved in the formation of the m/z 145 anion of β‐hydroxyamine pentafluoropropionate (PFP) derivatives observed under electron capture negative ion chemical ionization conditions occurs when the two functional groups are separated by up to five carbon atoms. Deuterium labelling has established that the site specificity, transfer of a hydrogen atom from the carbon adjacent to nitrogen to the OPFP group, is maintained in 4‐amino‐butan‐1‐ol‐N, O‐(PFP)2. The corresponding PFP derivatives of the N‐methylaminoalkanol‐(PFP)2 derivatives lack the m/z 145 species with m/z 163, [OPFP]− being the base anion. Substitution of alkyl groups on the carbon adjacent to oxygen results in a diminution of the ion intensity at m/z 145. with a marked increase in the intensity of m/z 144. The formation of the m/z 145 and 144 anions to proposed to proceed through the intervention of a fluoride ion‐molecule complex as outlined in Scheme 1 with the product ion distribution dependent on which of the two pathways is preferred.
Cyclopropane intermediates in the rearrangement and fragmentation of olefinic molecular ions
Authors: Laderoute Keith R. , Harrison Alex. G.
Published: May 2005

Methyl loss from deuterium‐labelled molecular ions of 4‐methyl‐2‐pentene, 2‐methyl‐2‐pentene and 1,1,2‐trimethylcyclopropane has been investigated for metastable molecular ions and for molecular ions formed by charge exchange with COS+˙, XE+˙ and CO+˙. For metastable ion fragmentation reactions all three compounds exhibit very similar behavior and show specific and essentially equal loss of each of the original methyl groups as well as specific loss of a methyl where the hydrogens derive exclusively from the non‐methyl hydrogens of the original molecules. The former results are interpreted in terms of interconversion of the three molecular ions through a ring‐opened form of the trimethylcyclopropane molecular ion. The loss of the non‐methyl hydrogens as CH3 is interpreted in terms of isomerization to the 2,3‐dimethyl‐2‐butene structure. With increasing internal energy direct allylic cleavage of the unrearranged methylpentene molecular ions increases in importance while the trimethylcyclopropane molecular ion shows an increased preference for loss of the C(2) methyl group. With increasing internal energy loss of the original non‐methyl hydrogens as CH3 decreases markedly in importance.
Effects of stepwise excitation on fragmentation of gas phase ions: An especially striking case
Authors: Kenttämaa H. I.
Published: May 2005

Dramatically different fragmentation patterns are obtained for 4‐ethyl‐2,6,7‐trioxa‐1‐phosphabicyclo‐[2.2.2]octane‐1‐oxide upon electron ionization (EI) and for the corresponding molecular ion on collision‐induced dissociation (CID). Two reasons for this behaviour have been discovered. (i) Irreversible multistep isomerization of the molecular ions occurs prior to collisional activation in mass spectrometry/mass spectrometry (MS/MS). Isomerization reactions have been characterized by isotopic labelling and by examining structures of relevant unlabelled and labelled fragment ions by MS/MS. The extent of isomerization can be controlled by varying the amount of internal energy of the molecular ions. This has been done by changing the number of thermalizing collisions which the ions undergo with neutral molecules in the ion source. (ii) When multiple collisions are used to dissociate the molecular ions, the initially stable fragmentation products undergo extensive further decomposition. As a result, abundant phosphorus‐containing fragment ions are obtained for the bicyclic phosphate in high‐pressure CID, whereas electron ionization leads to predominant hydrocarbon ions. A minor change in the structure of this molecule has major effects on the fragmentation behaviour: high‐ and low‐energy collisional activation spectra of the molecular ion of the corresponding phosphite are identical with the 12 e V EI mass spectrum of the neutral.
On the origin of fast forward moving ions generated from a repelled ion beam
Authors: Burgers Peter C.
Published: May 2005

Mass‐selected positive ions having kilovolt translational energies can be reversed in direction by applying a large voltage to a collision chamber situated in the second field‐free region of a reversed geometry instrument. It is shown that such repelled positive ions impinge on the earthed plate, situated in front of the chamber, leading to a variety of negative ions. The mass‐to‐charge ratios of these anions have been measured.
A comparison of electron impact mass spectrometry of isomeric pyranocoumarins (pyrano[3,2‐c][1]benzopyran‐5‐ones) and pyranochromones (pyrano[2,3‐b][1]benzopyran‐5‐ones)
Authors: Bravo Pierfrancesco , Ticozzi Calimero , Daolio Sergio , Traldi Pietro
Published: May 2005

The mass spectrometric behaviour of two pairs of isomeric 2,2‐dimethylpyrano[3,2‐c][1]benzopyran‐5‐ones (pyranocoumarins) and 2,2‐dimethylpyrano[2,3‐b][1]benzopyran‐5‐ones (pyranochromones) and four pairs of isomeric 2‐hydroxymethyl‐2‐methylpyrano[3,2‐c][1]benzopyran‐5‐ones (pyranocoumarins) and 2‐hydroxymethyl‐2‐methylpyrano[2,3‐b][1] benzopyran‐5‐ones (pyranochromones) has been studied in detail with the aid of exact mass measurements, linked scans, collisionally activated decompositions and deuterium labelling experiments. The presence in both series of compounds of the same ions derived by structural interconversion of both molecular ions is emphasized, and structural information on the ions [C7H5O2]+ (m/z 121), highly characteristic for these classes of compounds, as for 4‐hydroxycoumarins, is reported.
Analysis of free fatty acids by a micro‐liquid chromatograph directly coupled with a mass spectrometer through a vacuum nebulizing interface
Authors: Matsumoto K. , Yoshida H. , Ohta K. , Tsuge S.
Published: May 2005

A liquid chromatograph directly coupled with a quadrupole mass spectrometer through a vacuum nebulizing interface was applied to the analysis of various free fatty acids. Chemical ionization mass spectra of the C7C22 free fatty acids were first examined using either methanol or benzene as the reagents. Then the practical compositional analysis of the fatty acids were performed with various biological samples such as bean oil, rape oil, palm oil and milk fat where most of the fatty acids are included as their triglycerides.
Fast atom bombardment mass spectra of O‐isopropyl oligodeoxyribonucleotide triesters
Authors: Phillips Lawrence R. , Gallo Kathleen A. , Zon Gerald , Stec Wojciech J. , Uznanski Bogdan
Published: May 2005

The positive and negative fast atom bombardment (FAB) mass spectra of representative dimeric O‐isopropyl oligodeoxyribonucleotide triesters were recorded and examined. Features found to be shared among the FAB mass spectra of these compounds yielded important information regarding molecular weight, nucleobase composition and nucleotide sequence.
Charge stripping and the site of cationization of substituted aromatic compounds
Authors: Pachuta Steven J. , Isern‐Flecha Ileana , Cooks R. Graham
Published: May 2005

The site of protonation, methylation and ethylation of anilines, phenols and thiophenols can be determined by tandem mass spectrometry (MS/MS). The extent to which the cation attachment products formed from these compounds undergo charge stripping is related to the site of cation attachment. The formation of doubly charged ions for phenols and anilines is favored when cation attachment occurs on the ring. For thiophenols alkylation occurs almost exclusively on the substituent, and yet an abundant stripping peak is recorded. This behavior is opposite to that seen for anilines and phenols and is accounted for in terms of orbital energies in the three systems. The site of cation attachment, as deduced by charge stripping, agrees with conclusions drawn from the fragmentation behavior of these ions upon collision‐induced dissociation.
The effect of ion source temperature on the fragmentation of 2‐pentanone
Authors: Wood K. V. , McLuckey S. A. , Cooks R. Graham
Published: May 2005

A dramatic source temperature effect is observed in the low collision energy collision‐induced dissociation spectra of molecular ions derived via 70 eV electron bombardment of 2‐pentanone and via charge exchange. The observation cannot simply be attibuted to the increased thermal energy of the 2‐pentanone molecular ions. A number of factors appear to contribute to the observed results, (i) the increase, with temperature, in the ratio of the concentration of enol to keto neutral molecules, (ii) temperature effects on the Franck‐Condon factors which control the yields and internal energies of the keto and enol molecular ions, (iii) differences in the relative stabilities of the keto and enol molecular ions, (iv) temperature effects on the equilibrium between the isomeric molecular ions. This last item is probably most important, with the concentration of magnified image being most significant. These data highlight the role that ion source temperature can play as a variable in elucidating ion structure problems.
An unusual pathway for the elimination of hydrogen cyanide from benzonitrile upon electron impact as revealed by 13C and 15N labelling
Authors: Molenaar‐Langeveld Tineke A. , Fokkens Roel H. , Nibbering Nico M. M.
Published: May 2005

It is shown by 15N and specific 13C labelling that ∼50% of the molecules of hydrogen cyanide, eliminated within ∼10−6 s upon electron impact of benzonitrile, contains the original cyano carbon atom, whereas the remaining percentage contains one of the phenyl ring carbon atoms at random. This is even more dramatic for the molecular ions of benzonitrile which decompose in the first and second field‐free regions of the VG Micromass ZAB‐2F high‐field mass spectrometer used. Then only 5–7% of the eliminated molecules of hydrogen cyanide contains the original cyano carbon atom. A cycloaddition‐cycloreversion process in the molecular ions, leading to ionized 1‐cyano‐1,3‐hexadien‐5‐yne as an intermediate in the hydrogen cyanide loss, is proposed to explain this.
Evidence for long‐lived excited states of [CnH2]2+ carbodications
Authors: Appling J. R. , Shields G. C. , Moran T. F.
Published: May 2005

The energetics, structures, stabilities and reactivities of[CnH2]2+ ions have been investigated using computational methods and experimental mass spectrometric techniques. Spontaneous decompositions of [CnH2]2+ into [CnH]+ + H+ products, observed for ions with odd‐n values, have been explained by invoking the formation of excited triplet states. Even‐n [CnH]+ ions possess triplet ground states with low‐lying excited states, whereas odd‐n ions have triplet states with energies several eV above ground singlet states. Radiationless transitions of vibrationally excited long‐lived triplet state ions into singlet state continua are suggested as possible mechanisms for spontaneous deprotonation processes of odd‐n [CnH2]2+ ions. Evidence for these long‐lived excited states has been obtained in bimolecular single electron transfer reactions.
Stereospecific alcohol elimination from dialkyl mesaconates under electron impact: Another example of a hidden hydrogen transfer
Authors: Bornstein Daniel , Weisz Adrian , Mandelbaum Asher
Published: May 2005

Under electron impact dimethyl and diethyl mesaconates give rise to abundant [M  MeOH]+ and [M  EtOH]+ ions, respectively. The geometrically isomeric citraconates yield [M  MeO]+ and [M  EtO]+ ions. Mixed methyl ethyl mesaconates eliminate both methanol and ethanol. These findings, together with the results of a deuterium labelling study, indicate that the elimination of alcohol from the molecular ions of the mesaconates is partially preceded by a hidden hydrogen transfer step.
Mass spectroscopic fragmentation reactions. XXXI—the fragmentation behaviour of o‐halobenzoic acids substituted in the 5‐position: A novel ortho effect
Authors: Budzikiewicz H. , Breuer M.
Published: May 2005

A fragmentation sequence typical for o‐halobenzoic acids carrying a heteroatom substituent in the 5‐position is described.
Reactions induced by the γ‐hydrogen shift in the molecular ion of 1‐nitropropane
Authors: Hindawi S. K. , Fokkens R. H. , Pinkse F. A. , Nibbering N. M. M.
Published: May 2005

It is shown that the γ‐ or 1,5‐hydrogen shift in the molecular ion of 1‐nitropropane leads to three primary fragmentation reactions. They are the loss of a hydroxyl radical, a molecule of ethylene and a molecule of nitric oxide. The structures and chemistry of the resulting ions have been investigated by a series of experiments including deuterium labelling, spontaneous and collisionally induced dissociations and accurate mass measurements.
Mass spectrometric studies of heterocyclic organophosphorus compounds: 1,3,2‐benzodioxaphospholes
Authors: Hangzhou Guo , Tsao Kinghunt , Yu‐Gui Li , Wangjian
Published: May 2005

The mass spectral behaviour of a new type of organophosphorus compound, 1,3,2‐benzodioxaphospholes, under 70 eV electron impact has been studied by means of high and low resolution mass spectrometry as well as by B/E and B2/E linked scans. The influence of different substituents in the molecule (O, S or N) on the mass spectra is investigated. The reason for isomerization between oxygen and sulphur within a molecule studied by mass spectrometry is discussed.
Effect of method of ion preparation on low‐energy collision‐induced dissociation mass spectra
Authors: Nacson Sabatino , Harrison Alex. G. , Davidson William R.
Published: May 2005

The collision‐induced dissociation (CID) mass spectra of protonated cocaine and protonated heroin have been measured using a triple quadrupole mass spectrometer at 50 eV ion/neutral collision energy for protonated molecules prepared by different protonating agents. The CID mass spectra of protonated cocaine using H+(H2O)n, H+(NH3)n and H+((CH3)2NH)n as protonating agents are essentially identical and it is concluded that, regardless of the initial site of protonation, the fragmentation reactions occurring on collisional activation are identical. By contrast, protonated heorin prepared with H+(H2O)n and H+(NH3)n as protonating agents show substantial differences. That formed by reaction of H+(H2O)n shows a much more abundant peak corresponding to loss of CH3CO2H. From a comparison with model compounds, and from a consideration of the three‐dimensional structure of heroin, it is concluded that with H+(H2O)n as protonating agent significant protonation occurs at the acetate group attached to the alicyclic ring, leading to acetic acid loss on collisional activation, but that reaction of H+(NH3)n leads to protonation at the nitrogen function. The proton attached to nitrogen cannot interact with the acetate group and, consequently, the probability of loss of acetic acid on collislional activation is greatly reduced.
Ion chemistry of phthalamic acids. III. The origin of [M  1]+ ions under electron impact
Authors: Selva Antonio , Traldi Pietro , Ventura Paolo , Pellegata Renato
Published: May 2005

Electron impact mass spectra and collisional activation/mass‐analysed ion kinetic energy spectra of some phthalamic acids and their deuterium labelled analogues suggested that the genesis of [M  1]+ ions is due to the loss of an aromatic hydrogen ortho to the amidic group, as for aromatic amides and thioamides.
Fast atom bombardment mass spectra of monosulphonated merocyanine dyestuffs
Authors: Haessner R. , Borsdorf R. , Dube G. , Lehmann A. , Ruotsalainen H. , Bach G.
Published: May 2005

The FAB mass spectra of four sulphonated merocyanine dyes are investigated. Negative ion spectra are superior to those in the positive ion mode. The special structure of merocyanines with an acidic group at one end of the molecule and a basic group at the other leads to significantly different fragmentation pathways for positive and negative ions.
Fast atom bombardment mass spectra of isobaric/isomeric phosphonium salts
Authors: Kroha Kyle J. , Busch Kenneth L.
Published: May 2005

The positive ion fast atom bombardment mass spectra of isobaric/isomeric aryl phosphonium salts typically contain abundant intact cations, which can be used to establish the cationic molecular weight, characteristic ions that can be used to delineate structural subgroups, and fragment ions corresponding to losses of small neutral molecules. Several of the fragmentation pathways were elucidated by parent ion and daughter ion tandem mass spectrometry experiments. Dependence of the fragmentation reactions on functional group substitution suggests that fast atom bombardment mass spectrometry is an excellent method for the differentiation of isobaric/isomeric phosphonium salts used in synthetic organic and industrial catalytic processes.
Electron impact induced fragmentation of dihydro‐1,4‐oxathiines. 1. 2,3‐substituted 5,6‐dihydro‐1,4‐oxathiines
Authors: Nevalainen Vesa , Vainiotalo Pirjo
Published: May 2005

In the electron impact induced fragmentation of 2,3‐disubstituted 5,6‐dihydro‐1,4‐oxathiines, the cleavage of the heterocyclic ring proceeds through the retro Diels‐Alder type of reaction. The further fragmentation of the resulting radical cation gives rise to substituted carbonyl or thiocarbonyl cations. This fragmentation favours the formation of an ion which, in the electron‐deficient carbon‐oxygen or carbon‐sulphur triple bond, is stabilized by an electron‐releasing group. The ring fragmentation was observed to be dependent on the nature of the 3‐substituent of the ring when a series of 3‐substituted 5,6‐dihydro‐2‐methyl‐1,4‐oxathiines was investigated.
Acute pressure dependence of the electron ionization mass spectrum of molybdenyl acetylacetonate
Authors: Didonato G. C.
Published: May 2005

Formation of both fragment and polymeric ions observed in the electron impact mass spectrum of molybdenyl acetylacetonate exhibit a strong dependence on the instantaneous pressure in the ionization source. The indicated source pressure increases with increasing direct probe temperature. Utilizing a probe temperature increase of only 30°C min−1, the relative abundances of some ions can change by factors as high as 15 over a period of 60 s. Some ions are remarkably transient, appearing in only the few scans during which the source pressure corresponds to just that required for their formation. These rapid changes in the ion relative abundances are also exhibited in tandem mass spectra, and especially in parent ion scans.
Field ionization of high velocity neutral species. Rydberg states in noble gas atoms; the measurement of translational energy loss in neutralization‐reionization mass spectra
Authors: Bordas‐Nagy Jozsef , Holmes John L. , Mommers Alexander A.
Published: May 2005

The modification of a double‐focusing mass spectrometer of BE geometry (VG‐Analytical ZAB‐2F) to permit the field ionization of fast atoms in high Rydberg states is described. Field ionization was achieved by means of a pair of closely spaced, very fine metal meshes with a (kV) potential difference between them. High Rydberg noble gas atoms were generated from their ions by electron transfer from noble gas targets. Also described is a method, involving a field ionization observation, for measuring the net kinetic energy loss associated with the collision‐induced neutralization‐reionization of polyatomic ions.
Reactions of nucleophiles with triarylpropenones and triarylbutenones
Authors: Madhusudanan K. P. , Jain Raka , Mittal Shubhra , Durani Susheel , Kapil R. S.
Published: May 2005

From a study of the reactions of nucleophiles with 1,2,3‐triaryl‐propenones and‐butenones in a chemical ionization source it has been found that stronger nucleophiles, such as, MeO−, EtO− and MeS−, attack the α,β‐unsaturated system at the β‐carbon (Michael addition) or the carbonyl carbon giving rise to tetrahedral adducts, while weaker nucleophiles, such as, Cl− form the adduct ion by H‐bonding with the β‐hydrogen. The effect of substituents and source temperature supports the operation of these processes. The triaryl butenone did not give the adduct ion with MeO− as deprotonation leads to a stable [M  H]− ion.
Electron impact induced cyclizations in 4‐chioro‐3‐(N‐aryliminomethyl) (2H) benzopyrans and benzothiopyrans
Authors: Ramana D. V. , Balasubramanian K. K. , Srinivas R. , Saiganesh R. , Swaminathan K.
Published: May 2005

Intramolecular substitutions leading to cyclizations with the ejection of chlorine have been noticed during mass spectral fragmentation of 4‐chloro‐3‐(N‐aryliminomethyl) (2H) benzopyrans and benzothiopyrans. Very interesting ortho effects involving intramolecular substitutions have also been observed in 6‐methyl‐4‐diloro‐3‐[N‐(2‐methoxyphenyliminomethyl)] (2H) benzopyran and 6‐methyl‐4‐chloro‐3‐[N‐(2‐chlorophenyliminomethyl)]‐(2H) benzopyran. The proposed fragmentation mechanisms have been supported by the accurate mass measurements and linked scan studies.
Diethylhydrogensilyl cyclic diethylsilylene derivatives in gas chromatography/mass spectrometry of hydroxylated steroids. III‐Fragmentations of 5β‐pregnane‐17,20,21‐triol derivatives
Authors: Nakatat Hisao , Ishibashi Masataka , Itoh Masahiro , Miyazaki Hiroshi
Published: May 2005

A reaction of N,O‐bis‐(diethylhydrogensilyl) trifluoroacetamide with 5β‐pregnane‐17,20,21‐triols afforded diethylhydrogensilyl (DEHS) cyclic diethylsilylene (DES) derivatives. 5β‐Pregnane‐3α,17α,20β,21‐tetraol yielded the 3α,21‐bis‐DEHS‐17α,20β‐DES compound, whereas the structure of the major product from its 20α isomer was assigned as the 3α,17α‐bis‐DEHS‐20α,21‐DES derivative, which would undergo facile isomerization to the unstable 3α,21‐bis‐DEHS‐17α,20α‐DES structure under electron ionization. Fragmentations of these DEHS‐DES compounds are discussed on the basis of isotope labelling experiments, linked scanning data, and accurate mass measurements.
Water loss from molecular protonated ions of benzyl 2‐phenylethyl ether and derivatives
Authors: Kingston Eric E. , Shannon James S. , Lacey Michael J.
Published: May 2005

The skeletal rearrangement for water loss is the dominant ion reaction in the chemical ionization mass spectrum of benzyl 2‐phenylethyl ether. Isotopic distributions obtained for this reaction with specifically labelled derivatives have been interpreted in terms of competing five‐ and six‐centred skeletal rearrangements. Chemical substitution of the alternative aromatic rings strongly influences the balance of the competition.
Analysis of polymer surfaces by SIMS: 7. Homopolymer and copolymer nylons
Authors: Briggs D.
Published: May 2005

Static secondary ion mass spectra (positive and negative) have been obtained from spin‐cast films of nylon−3, −4, −6, −7, −8, −11, −12, −46, −66 and −610 homopolymers, as well as nylon−6/66 copolymers covering the composition range. All spectra are highly characteristic and feature protonated multiple repeat unit fragments. Relative peak intensities from the nylon−6/66 copolymers correlate with composition. Overall, the fragmentation patterns bear a strong resemblance to high temperature pyrolysis mass spectra from these polymers.
SCN· loss by intramolecular substitution of electron impact ionized 3‐cyano‐5‐thiocyanatoalka‐2,4‐dienoic acid esters
Authors: Herzschuh R. , Schulze B. , Mühlstädt M.
Published: May 2005

The behaviour of some 5‐thiocyanatoalkadienoic acid esters under electron impact has been investigated by means of low‐resolution mass spectrometry. Some characteristic rearrangement processes have been observed under SCN· radical loss.
Silver sulfonates. A novel calibration material for field desorption mass spectrometry
Authors: Espinosa‐Leniz Rafael , White Edward
Published: May 2005

An equimolar mixture of silver methanesulfonate and silver trifluoromethanesulfonate has been investigated as a calibration material for exact mass determination in field desorption mass spectrometry. The mass scale was established using only field desorption by double exposure of the calibration material and the sample on a photographic plate. The precision and the accuracy of the method were tested by recording the mass spectra of a variety of peptides of known composition at a resolution of about 4000. The results indicate that the mass scale established is useful for the determination of the exact masses of field desorbed ions over the mass range examined: m/z 294–1147.
Mass spectrometry of substituted 1,3‐dihydro‐2H‐imidazole‐2‐thiones
Authors: Cert Arturo , Péerez‐Lanzac Mariana Trujillo
Published: May 2005

The electron impact mass spectra of the 4‐formyl‐1, 3‐dihydro‐2H‐imidazole‐2‐thione, its six 1‐methyl(n‐propyl, n‐hexyl)‐3‐methyl(phenyl)‐disubstptuted derivatives, and the 1,3‐dihydro‐1‐phenyl‐2H‐imidazole‐2‐thiome are discussed. The fragmentation pattern is strongly influenced by the alkyl or phenyl N‐substituents, as well as by the length of the alkyl chain. The odd‐electron ions containing an N‐phenyl substituent, but not a propyl or hexyl group, eject a hydrogen atom from the phenyl ring, while the presence of a long alkyl chain greatly enhances the loss of the sulphyhydryl radical and facilitates the expulsion of several alkenes, and alkyl and alkenyl radicals.
Fast atom bombardment mass spectra of some alkylammonium 4‐toluenesulfonate salts
Authors: Furton Kenneth G. , Poole Coliu F.
Published: May 2005

The fast atom bombardment positive ion mass spectra of low molecular weight alkylammonium 4‐toluenesulfonate salts are dominated by cluster ions of the type [(AB)nA]+ or [(AB)nH]+, where A is a cation, B an anion, n an integer from 0 to 4. With one exception the base peak is the cation A+.
Fast atom bombardment induced ring rupture of silatranes
Authors: Yan Lin , Chai Wengang , Wang Guanghui , Wu Guanli , Lu Kaijuan , Luo Yue
Published: May 2005

During a comparison study of the fast atom bombardment (FAB) and electron impact mass spectra of 1‐organyl‐2,9,10‐trioxa‐6‐aza‐1‐silatricyclo[4.3.3.01,6]dodecanes, an unusual ion peak at m/z 164 was noticed in the FAB spectra. Accurate mass measurement indicated that m/z 164 corresponds to protonated 1‐[N,N‐bis(2‐hydroxyethyl)amino]‐1‐propanol (BHAP), which is produced by a ring‐rupture reaction. Further experiment showed that the intensity of the [BHAP + H]+ ion peak increased markedly as the 7keV Ar0 bombardment proceeded, suggesting a FAB‐induced reaction. The possible mechanism is also discussed.
Free radicals formed by ion beam neutralization of [DCO]+, [DOCO] +, [CD3OD2]+ and [(CD3)2COD] + on metal targets
Authors: Raksit Asit B. , Porter Richard F.
Published: May 2005

A series of radicals formed when a fast beam of deuterated ions, [DCO] +, [DOCO] +, [CD3OD2]+ and [(CD) 2COD] +, is neutralized by electron transfer from K. Na and Zn atoms has been studied by a combination of charge stripping and beam scattering techniques For all systems studied, some fraction of The radicals from charge exchange are formed in excited dissociative states. Radical decomposition products have been identified and fragmentation energies have been measured. A metastable slate of CD3GD2 is observed with a lifetime greater than 0.5 μs. Stable radicals of DCO and (CD3)2 COD are formed by ion–Zn charge exchange. Indirect evidence indicates that [DCO] +–K charge exchang; leads to an excited radiative state of the radical.
Collision‐induced dissociations of substituted benzyl anions: Deprotonated 2‐Phenyl‐1,3‐dithiane
Authors: Bowie John H. , White Peter Y. , Blumenthal Thomas
Published: May 2005

Deprotonated 2‐phenyl‐1,3‐dithiane undergoes competitive losses of H˙, C3H6 C2H4S, C3H4S, C7H6S, C10H10 and C10H10S upon collisional activation. The elimination of H occurs from the phenyl ring. The loss of C3H6 occurs by simple cleavage of the dithiane ring. All other processes involve specific proton transfer followed by either cleavage or internal nucleophilic displacement.
Electron impact induced fragmentation of dihydro‐1,4‐dithiines. 2,3‐Substituted 5,6‐dihydro‐l,4‐dithiines
Authors: Nevalainen Vesa , Vainiotalo Pirjo
Published: May 2005

In the electron impact induced fragmentation of 2,3‐disubstituted 5,6‐dihydro‐1,4‐dithiines, the most important cleavage of the heterocyclic ring occurs via the retro‐Diels‐Alder type of reaction. The further fragmentation of the resulting radical cation gives rise to substitutes thiocarbonyl cations. This fragmentation favours formations of ions in which the electron‐deficient carbon‐sulphur triple bond is stabilized by an electron‐releasing group. The ring fragmentation was observed to be dependent on the nature of the 3‐ and 2‐substituents of the ring when a series of 3‐ and 2‐substituted 5,6‐dihydro‐l,4‐dithiines was investigated. The fragmentation of dihydro‐l,4‐dithiines partly resembles the fragmentation of the corresponding dihydro‐l,4‐oxathiines. The presence of the two sulphur atoms in dihydro‐l,4‐dithiines give rise to more stable molecular ions than observed in the case of the dihydro‐1,4‐oxathiine analogues. Fragmentations of dihydro‐l,4‐dithiines can also involve extrusions of alkylradicals or HS‐radical from the heterocyclic rings of molecular ions.
A data acquisition system for mass‐analyzed ion kinetic energy spectra using a personal computer
Authors: Traeger John C. , Mommers Alexander A.
Published: May 2005

An inexpensive data acquisition system has been developed for mass‐analyzed kinetic energy experiments which involve scanning the electrostatic analyzer of a reversed geometry mass spectrometer. The various hardware and software design features are described. Results for data obtained with a commercially available VG ZAB‐2F mass spectrometer are presented and discussed.
Isobutane chemical ionization mass spectra of unsaturated alcohols
Authors: Munson Burnaby , Feng Ta‐Min , Ward Harry D. , Murray Roger K.
Published: May 2005

Analysis of the isobutane chemical ionization mass spectra of hexenols, cyclohexenols and various syn/anti pairs of bicyclic and tricyclic homoallylic alcohols shows that: (i) the spectra of the allylic alcohols are dominated by [M + H – H2O]+ and [M + C4H9–H2O]+ ions and contain traces of [M + H]+ ions; (ii) [M + H]+ ions are prominent in the spectra of acyclic and certain cyclic homoallylic alcohols; and (iii) [M + H]+ ions dominate the spectra of other acyclic unsaturated alcohols. The [M + H]+ ions may result from either: (a) protonation of the hydroxyl group, followed by a very rapid intramolecular proton transfer from the protonated hydroxyl group to the carbon–carbon double bond or internal solvation of the protonated hydroxyl group by the carbon–carbon double bond; and/or (b) direct protonation of the carbon–carbon double bond with significant internal solvation of the resulting carbocation by the hydroxyl group, which may lead to carbon–oxygen bond formation to give a protonated cyclic ether. The consequences of placing various geometric constraints on the possible intramolecular interactions between the hydroxyl group and the carbon–carbon double bond in unsaturated alcohols are explored.
Mass analysis of overlapping ion kinetic energy peaks arising from charge separation in dications
Authors: March R. E. , Harrison A. G. , Young A. B.
Published: May 2005

A triple‐sector instrument of reversed geometry, BEQQ, has been employed to resolve overlapping ion kinetic energy peaks arising from charge separation of metastable dications. Separation was achieved through mass resolution of the dication in the magnetic sector and of the singly charged product ion of greater mass in the quadrupole mass filter accompanied by energy resolution with the electric sector; the electric sector was scanned to cover the complete range of each charge separation peak. Two overlapping ion kinetic energy peaks arising from charge separation of the diphenylenimine dication and up to four overlapping ion kinetic peaks arising from charge separations of dications arising from benzene‐1,3,5‐d3 have been resolved. The kinetic energy releases have been calculated in each case. Enhanced z‐discrimination is observed with the final stage of mass analysis.
Consecutive reactions in the vitamin D series. A New insight into the mechanism of vitamin D and provitamin D isomerizations in the mass spectrometer
Authors: Zaretskii Z. V. I. , Singh S. , Kingston E. E. , Harris F. M. , Beynon J. H.
Published: May 2005

The individual steps of the consecutive reactions
equation image
arising from metastable molecular ions, derived from vitamin D3, vitamin D2 and their respective provitamins (7‐dehydrocholesterol, ergosterol), were examined in different field‐free regions of a triple‐sector mass spectrometer of B/E/E geometry. The comparison of the translational energy release (T) and the metastable peak shapes corresponding to these reactions, as well as unimolecular and collision‐induced dissociation mass‐analysed ion kinetic energy spectra, showed that there are probably two structures of the [M – H2O]+˙ and [M – CH3˙]+ ions depending upon whether the respective ions are formed in the ion source through high‐energy reactions, or from the fragmentation of metastable molecular ions through slow, low‐energy processes which occur in the first field‐free region.
Effects of functional group interactions in the chemical ionization mass spectra of some substitutedcis‐1,3‐cyclopentane dicarboxylic acids and their derivatives
Authors: Vainiotal Pirjo , Mälkönen Pentti J.
Published: May 2005

Ammonia, isobutane and methane chemical ionization mass spectra have been measured for some substitutedcis‐1,3‐cyclopentane dicarboxylic acids and their derivatives. The relative proton affinities of the different functional groups determine the protonation site in the molecule and thereby greatly affect the fragmentation. Intramolecular catalysis clearly facilitates the elimination of water in cases where functional groups can interact with each other.
Relative molecular mass information from aliphatic nitro compounds: A chemical ionization study
Authors: Ballantine James A. , Barton Jonathan D. , Carter James F. , Davies Jeremy P. , Smith Keith , Stedman Geoffrey , Kingston Eric E.
Published: May 2005

The mass spectra of a number of aliphatic nitro compounds have been studied using electron Ionization (EI) and a variety of chemical Ionization (CI) techniques in attempts to obtain relative molecular mass information. The use of positive ion ammonia chemical Ionization techniques gave very satisfactory results, providing abundant [M + NH4]+ ions, not only from both primary and secondary nitro compounds, but also from the much more labile tertiary nitro compounds. However, the use of methane and isobutane positive ion CI or EI conditions resulted in facile fragmentation with little relative molecular mass information being made available. Negative ion CI using methane, isobutane or ammonia as moderating gases all gave abundant [M − 1]− ions with primary and secondary nitro compounds but at much reduced sensitivity.
Bifunctional even‐electron ions. III. Fragmentation behaviour of aliphatic hydroxonium ions containing an additional carbomethoxy group
Authors: Záluorszky U. I.
Published: May 2005

The primary and subsequent fragmentations of the bifunctional oxonium ions \documentclass{article}\pagestyle{empty}\begin{document}${\rm R} \!-\! \mathop {\rm C}\limits^ + ({\rm OH})\! -\! ({\rm CH}_2)_n \! - \! {\rm COOCH}_3 $\end{document} (n = 0−5), a, are dominated by functional group interactions. Loss of CH3OH is the only appreciable primary fragmentation of the higher homoiogues, but for the lowest homologue (a0) this reaction is missing. Instead, CO loss is observed. The next homologue (a1) shov.s loss of CH2CO besides loss of CH3OH. The mode of the subsequent fragmentations is dependent on the chain length separating the functional group, and formation of cyclic ions is typical of the fragmentation behaviour of a2 and a3. Evidence for proton transfer from the carbonyl oxygen to the methoxy group of a protonated ester group is presented.
Unimolecular fragmentation reactions of protonated and methyl‐cationated n‐octanones and N‐nonanones. Sequential fragmentation reactions
Authors: Chowdhury Swapan , Harrison Alex G.
Published: May 2005

Protonated and methyl‐cationated n‐octanonts and n‐nonanones have been prepared by chemical ionization methods and the unimolecular fragmentation reactions occurring on the metastable ion time‐scale have been exam ined. The [R1R2COR3]+ (R3 = H or CH3) species fragment by elimination of R3OH and by elimination of neutral alkenes. The elimination of (R1 — H), where R1 is the larger alkyl group of the original ketone, is particularly important. In addition, alkenyl ions are observed corresponding, nominally, to elimination of C3H7OR3 from the ionized octanones and to elimination of C3H7OR3 and C4H9OR3 from the nonanones. These ions are shown to arise largely, if not completely, by sequential elimination of R3OH plus an olefin (C3H6 or C4H8) from [R1R2COR3]+. A comparison is made of the unimolecular fragmentation reactions occurring in the second field‐free region and in the radio‐frequency‐only quadrupole of a hybrid BEQQ mass spectrometer.