Reaction from isomeric parent ions in the dissociation of dimethylpyrroles

The major dissociation pathways of the [M-H]⁺ (loss of NH₃ or CH₄) and the [M+H]⁺ (loss of NH₃ or CH₃) ions from dimethylpyrroles have been determined to occur from isomeric parent ions. For the [M-H]⁺ ion (formed by loss of a methyl hydrogen), loss of NH₃ leads to the formation of the phenylium ion and is preceded by consecutive carbon ring expansions followed by a ring contraction to form protonated aniline. Loss of CH₄ occurs after the first carbon ring expansion, which forms protonated picoline. The relative partitioning between the two dissociation paths depends upon the internal energy content of the parent ion; the highest point on the potential energy surface is the second ring expansion step. The [M+H]⁺ ion reacts through a similar pathway via dihydro analogs of picoline and aniline. The proposed reaction pathways are supported by results of semiempirical molecular orbital calculations.     

Ortho,Effects in organic molecules on electron impact: X—unusual ortho effects of the methyl group in o-picolinotoluidide

The mass spectrum of o-picolinotoluidide gives rise to three major fragments at m/z 184, m/z 169 and m/z 168, corresponding to the loss of CO from the molecular ion followed by the loss of ?H₂ and ?H₃ by independent pathways. It has been shown that the ortho methyl group and the nitrogen of the pyridine ring in the 2-position are involved in the formation of these three major fragments observed in the mass spectrum of o-picolinotoluidide. The mass spectrum of 2-(o-toluidino) pyridine, the molecular ion of which can resemble the [M? CO]⁺ ion in o-picolinotoluidide, also shows loss of CH₃ and NH₂ radicals from the molecular ions. Based on these observations coupled with the high resolution data, the mass analysed ion kinetic energy spectrometry and high voltage scans of these fragments in both the compounds, two mechanistic pathways have been proposed for the formation of these ions in o-picolinotoluidide.     

Electron-impact induced skeletal re-arrangement of 2-methoxy-3-methylpyrazine and 2-methylthio-3-methylpyrazine

The mass spectra of 2-methoxy-3-methylpyrazine (I), 2-methoxy-6-methylpyrazine (II), 2-methylthio-3-methylpyrazine (III) and 2-methylthio-6-methylpyrazine (IV), are given and the major fragmentation pathways discussed. The novel loss of H₂O from the molecular ion of I and the corresponding loss of H₂S from the molecular ion of III indicate that a skeletal rearrangement takes place in the molecular ion preceding the expulsion of H₂O and H₂S. Proposed mechanisms for this behavior are discussed with evidence being drawn from accurate mass measurement, metastable ions, and deuterium and carbon-13 labeling of the methoxy group. The absence of ions in the spectra of II and IV corresponding to the loss of H₂O and H₂S from these molecular ions clearly indicates that the position of the methyl group with respect to the methoxy group, or the methylthio group is in-timately involved in this mechanism.     

Pyrones. II—the mass spectra and fragmentation mechanisms of methyl maltol (3-methoxy-2-methyl-4H-pyran-4-one) and methyl allomaltol (5-methoxy-2-methyl-4H-pyran-4-one)

The mass spectra of methyl maltol (3-methoxy-2-methyl-4H-pyran-4-one) and methylallomaltol (5-methoxy-2-methyl-4H-pyran-4-one) and a number of deuterium labelled analogues have been studied in detail. The two pyrones have common fragmentation pathways, all of which can be traced back to a primary rearrangement of the molecular ion. The loss of water from the molecular ion occurs by two processes, both involving the methoxymethyl protons. The loss of methyl from the molecular ion also occurs by two routes, only one of which involves the methoxy methyl protons directly.     

Mass spectral fragmentation of benzofurazan-1-oxide

Fragmentations in the mass spectrum of benzofurazan-1-oxide have been studied using linked scan, accelerating voltage scan and mass-analysed ion kinetic energy spectrometric techniques. Major pathways involve NO·+ NO· and NO·+CO loss, these double losses occurring in such rapid succession as to appear ‘concerted’ in some experiments. Minor pathways are loss of CO₂, C₂N₂O₂, or C₂HN₂O₂ from the molecular ion. The major fragment ion, m/z 76, in the conventional mass spectrum is not detected in a mass-analysed ion kinetic energy spectrometric experiment with the molecular ion until collision activation is provided. The conventional electron impact spectrum invariably includes ions from benzofurazan which is produced by thermal deoxygenation in the source.     

Metastable ion studies. 4—mass spectral fragmentation and isomerization in the esters of chlorinated propenoic acids

Metastable peaks have been used to study the fragmentation pathways of the methyl and trideuteriomethyl chloropropenoates and chloromethyl propenoate. The molecular ion peaks of the unsaturated esters are more intense than those of the saturated esters, α-Cleavage, [M? OCH₃]⁺, produces the base peak in almost all compounds, the relative abundances of the additional peaks being low for chloromethyl propenoate. The losses of H₂O, CH₃^. and COOH^. indicate the isomerization of some ionized chloro esters to the chlorinated 2-butenoic acid molecular ions. An intense loss of H₂O observed for methyl 2-chloropropenoate indicates its most facile isomerization, [ester]^+˙ → [acid]^+˙, whereas the isomerization in methyl trichloropropenoate could not be observed. The molecular ion of chloromethyl propenoate, however, also seems to partly rearrange to the chlorinated 3-butenoic acid ion, since the first field free region metastable peak shows a weak loss of CO. The new reaction pathways, i.e. the losses of CHO^˙, CH₂O and CH₂CO from ionized chloromethyl propenoate, were detected.     

Mass spectra of new heterocycles: XVI. Electron impact study of alkyl 5-aminothiophene-2-carboxylates

Electron impact mass spectra of alkyl 4-alkoxy-5-amino-3-methylthiophene-2-carboxylates were studied for the first time. These compounds, except for 4-(1-ethoxyethoxy) and 4-(ferrocenylmethoxy) derivatives, give rise to a stable molecular ion whose decomposition follows three pathways. The main fragmentation pathway of the molecular ion is elimination of alkyl radical from the 4-alkoxy group, the second pathway involves expulsion of alkoxy group from the ester moiety, and the third pathway is decomposition of the thiophene ring. The molecular ions of 4-(1-ethoxyethoxy)thiophenes decompose mainly via elimination of ethyl vinyl ether molecule with formation of [M–VinOEt]⁺ · odd-electron ion, and fragmentation of the latter follows general pathways. In the mass spectra of 4-(ferrocenylmethoxy)thiophenes the most abundant are ferrocenylmethyl ion with m/z 199 (I _rel 100%) and fragment ions derived therefrom.     

Mechanism of ionization and initial fragmentation in electron impact mass spectra of 3-halogenobenzanthrones

Electron-impact mass spectra of 3-halogenobenzanthrones (halogen X = Cl, Br, I) were measured and ionization efficiency curves and three kinds of linked-scan spectra were obtained for several fragment ions. The fundamental mechanisms of ionization and initial fragmentation were interpreted by the penetration length of an impacting electron or the density distribution on the molecular surface of a rejected electron and its orbital energy. The apparent ionization energy (IE) of a singly charged molecular ion seems to be the lower one of non-bonding electrons on O or X, and that of a doubly charged molecular ion the sum of three terms, the IE of non-bonding electron on O, that on X and the electrostatic repulsion between two positive charges. Two competing pathways of decomposition from the molecular ion M^+· to an ion [M - CO,- X]⁺ were observed: one is the initial detachment of CO in chloro and bromo compounds and the other is the initial elimination of the iodine atom in the iodo compound. The sequence of these reactions was confirmed by metastable ion analysis with linked-scan spectra and the relative magnitudes of the appearance energies. They can be explained by the driving force of a localized positive charge or unpaired electron on a heteroatom.     

Two-body Coulomb explosion in methylacetylene in intense laser fields: double proton migration and proton/deuteron exchange

Two-body decomposition processes of methylacetylene (CH(3)CCH) and its isotopomer methyl-d(3)-acetylene (CD(3)CCH) in intense laser fields (790 nm, 40 fs, 5.0 × 10(13) W cm(-2)) are investigated by the coincidence momentum imaging (CMI). In methyl-d(3)-acetylene, a total of six decomposition pathways in which one of the C-C bonds is broken and a total of six pathways in which an atomic hydrogen ion (H(+) or D(+)) or a molecular hydrogen ion (H(2)(+), HD(+), D(3)(+), or HD(2)(+)) is ejected are identified. It is revealed from the analysis of the CMI data that the migration of two deuterons as well as the exchange between a proton and a deuteron occurs prior to the two-body decomposition of a doubly charged parent molecule.     

Mass spectral fragmentation pathways of N-acetylnitramines: 1-acetylhexahydro-3,5-dinitro-1,3,5-triazine and 1-acetyloctahydro-3,5,7-trinitro-1,3,5,7-tetrazocine

Mass spectra of the N-acetylnitramines l-acetylhexahydro-3,5-dinitro-l,3,5-triazine (TAX) and 1-acetyloctahydro-3,5,7-trinitro-l,3,5,7-tetrazocine (SEX) were recorded in electron impact (EI) and positive and negative chemical ionization (PCI and NCI) modes, and the fragmentation pathways were compared with those of other nitramines which have been well documented and characterized. Unexpectedly, for both acetylnitramines in the EI mode (and in the PCI mode) proton adducts were the only molecular ion species observed; in neither mode was there evidence for higher adducts. In contrast, for TAX in the NCI mode the [M + NO₂]^? adduct was the second most abundant ion (70%); relatively small amounts of the [M + NO]^? adduct (2%) and the hydrogen adduct [MH]^? (3%) were observed. Under identical NCI conditions no molecular ion species or adduct ions were detected for SEX; the ion of highest m/z corresponded to loss of NO₂ or HNO₂ from a molecular ion species. The findings of collision-induced dissociation experiments are also discussed.     

Mass spectra of N and O methyl and methylthiomethyl derivatives of benzophenone oxime

The mass spectra of benzophenone oxime O-methyl and O-methylthiomethyl ethers, α,α-diphenyl-N-methyl and methylthiomethyl nitrones, and some deuterated analogues, are reported. Fragmentation pathways are discussed, with particular reference to the structures of ion m/e 211 found in all the spectra. Some evidence suggests nitrone → O-ether rearrangement at either neutral molecule or molecular ion level.     

A combined time-resolved and stereospecific deuterium labelling study of the elimination of methanol from the molecular ion of methoxycyclohexane

It is shown by field ionization kinetics in combination with both site-specific and stereospecific D-labelling that the loss of a molecule of methanol from the molecular ion of methoxycyclohexane can occur via 1,4- and 1,3-eliminations. The 1,4-elimination predominates at molecular ion lifetimes of ≥10^?10.1 s. It is found that ～19% of this reaction channel corresponds to a stereospecific cis-elimination, whereas the remaining 81% is only site-specific. At molecular ion lifetimes of between 10^?10 and 10^?9 s, a very sudden increase of the 1,3-elimination is observed at the expense of the 1,4-elimination. A stereospecific loss of methanol, however, is not observed at all for the 1,3-elimination within the limits of error. Possible intermediates and reaction pathways, which can account for the observations made, are discussed.     

Electron impact induced fragmentation of some 7-(o- and p-R-benzylidene)-3-(o- and p-R-phenyl)-3,3a,4,5,6,7-hexahydro-2H-indazoles. I

The mass spectral fragmentation patterns of ten 7-(o- and p-R-benzylidene)-3-(o- and p-R-phenyl)-3,3a,4,5,6,7-hexahydro-2H-indazoles, I, obtained by electron impact have been studied. All the spectra analyzed contain molecular ions and the principal fragmentation routes take place either from the molecular ion, or from (M⁺-1) ion. Likewise, our investigation of the mass spectra of these compounds revealed interesting relationships between the substitution pattern in the framework of I and the fragmenation pathways.     

The mass spectrum and fragmentation mechanism of exo- and endo- norborneol

The mass spectra of exo -and endo-norborneol and a number of deuterium labelled and-logues have been studied in detail. The two alcohols have common fragentation pathways, the major routes of which can be related to specific rearrangements of the molecular ion. The loss of water from the molecular ion consists of two processes, one involving and one4 not involving the hydroxyl hydrogen atom. The limitions of the labelloing experiements are discussed.     

A New Sodium Thioborate Fast Ion Conductor: Na3B5S9

We report a new sodium fast-ion conductor, Na₃B₅S₉, that exhibits a high Na ion total conductivity of 0.80 mS cm⁻¹ (sintered pellet; cold-pressed pellet=0.21 mS cm⁻¹). The structure consists of corner-sharing B₁₀S₂₀ supertetrahedral clusters, which create a framework that supports 3D Na ion diffusion channels. The Na ions are well-distributed in the channels and form a disordered sublattice spanning five Na crystallographic sites. The combination of structural elucidation via single crystal X-ray diffraction and powder synchrotron X-ray diffraction at variable temperatures, solid-state nuclear magnetic resonance spectra and ab initio molecular dynamics simulations reveal high Na-ion mobility (predicted conductivity: 0.96 mS cm⁻¹) and the nature of the 3D diffusion pathways. Notably, the Na ion sublattice orders at low temperatures, resulting in isolated Na polyhedra and thus much lower ionic conductivity. This highlights the importance of a disordered Na ion sublattice—and existence of well-connected Na ion migration pathways formed via face-sharing polyhedra—in dictating Na ion diffusion.     

The behaviour of stereoisomeric ions in the gas phase: 3—The case of homosubstituted bicyclooctenes

In the electron impact mass spectroscopy of four 2,3,5,6-bicyclo(2.2.2)–7-octenetetramethoxycarbonyl stereoisomers differences in relative abaundances of product ions and also different fragmentation pathways are observed. The stereospecificity is retained also under positive ion chemical ionization (CI(methane), CI(isobutane)) and negative ion chemical ionization (NICI) (OH^?) conditions. Interesting correlations between fragmentation and molecular symmetry are suggested.     

Kinetic and spectroscopic characterization of the isomers of the allyl bromide molecular ion

The kinetics of the ion/molecule reactions of the molecular ion of allyl bromide (3-bromopropene), C₃H₅Br⁺., with its neutral show that only (82 ± 2)% of these ions are reactive. This percentage is mildly sensitive to ionization energy below 13 eV, but is pressure insensitive. The collisionless infrared multiphoton-induced photofragmentation of these ions at 10.25 μm and at variable power densities is consistent with the presence of two ionic species in the ratio obtained from the kinetic experiments. The most abundant species undergoes much faster photofragmentation at this wavelength, but at 10.59 μm the photofragmentation rates become comparable. Experiments performed by isolating the remaining molecular ions after completion of the ion/molecule reaction confirm that the unreactive species corresponds to the slow photodissociating ion at 10.25 μm. A combination of kinetic experiments and photodissociation is used to establish that the less abundant species behaves unlike the molecular ion obtained from 1-bromopropene, 2-bromopropene, or bromocyclopropane. The two structures for the molecular ion are shown to originate from ionization and not by isomerization through collisions.     

A mass spectral study of the acid-catalysed oxygen exchange in laevulinic acid

The sequence, i.e. site selectivity of the acid-catalysed ¹⁶O/¹⁸O exchange in laevulinic acid (1) is studied by mass spectrometry, ion kinetic energy spectroscopy and accurate mass measurements on 1 and its ¹³C(1)-labelled congener. In the fragmentation pathways all ions of interest in the spectrum of 1 originate from the molecular ion, which may exist in six tautomeric or isomeric forms (1a–1d). The mechanism of gas-phase cyclization of 1a is rationalized in terms of three different pathways. Formation of the most prominent fragment ions and the sequence of ¹⁶O/¹⁸O exchange at the carbonyl and carboxy group are discussed. The results indicate the ions of m/z 56, m/z 61 and m/z 98 to be the only three which have incorporated oxygen atoms originating from the carboxy group in 1 and could thus be used in further elucidadon of the rearrangement mechanism of 5-hydroxymethylfuran (2) or 5-hydroxymethylfuran-2-carbaldehyde (3) into laevulinic acid (1).     

Effect of the structure of alkoxy radicals on the mass-spectral fragmentation of dialkyl alkylphosphonates

Basic fragmentation reaction of dialkyl alkylphosphinates under the conditions of electron ionization proceeds in two steps. In the first step occurs cleavage of C-O bond and splitting the olefin radical off. The intermediate ion formed therewith exerts further fragmentation by the similar way. Peaks of the intermediate ions occurs in the spectra of all dialkyl alkylphosphonates except O-methyl derivatives. In the case of branching at α-carbon atoms of alkoxy radicals cleavage of the first carbon-carbon bond of the alkoxy radical unlike the case of alkyl fluorophosphonates, in the intermediate ion rather than in molecular ion and accompanied by the elimination of alkane. These found regularities allow to explain principal fragmentation pathways of a wide series of phosphoric acids esters of general formula (RO) _n P(O)X _n?3 (where X is R, Hal, or OMe) with both linear and branched in α-position alkoxy radicals.     

Recherches en Serie Azabenzodiazepine. III—Fragmentation en Spectrometrie de Masse de Quelques Pyrido,Pyrimido, Pyrazolodiazepinones,Triazino et Triazolotriazepinones

The mass spectra of several pyrido [2,3-b] and [3,4-b], pyrimido [4,5-b], pyrazolo [3,4-b] diazepinones-1,4 and as-triazino [4,3-b], s-triazolo [4,3-b]triazepinones-1,2,4 are reported and analysed. Five different fragmentation pathways of the molecular ion are generally observed, but the main one is an initial loss of CH₂CO which gives rise to 2-methylazabenzimidazole or 2-methyl azabenzotriazole ions. The behaviour of triazolotriazepines which have two further fragmentation pathways is described.