Mass spectrometry of aryl substituted di- and trisiloxanes

The mass spectra of arylpentamethyldisiloxanes, sym-diaryltetramethyldisiloxanes and 1,5-diaryl-1,1,3,3,5,5-hexamethyltrisiloxanes were examined. Isotopic labeling and peak matching were used to substantiate the proposed fragmentation mechanisms. Siliconium ions dominate the spectra. Loss of neutral fragments from the [M-15]⁺ ions is important. Phenylpentamethyldisiloxane, sym-tetramethyldiphenyldisiloxane and 1,1,3,3,5,5-hexamethyl-1,5-diphenyltrisiloxane are representative examples of the three classes of compounds discussed. The [M-15]⁺ ion of phenylpentamethyldisiloxane loses methane, dimethylsilanone [(CH₃)₂Si?O] and phenylmethylsilanone [PhCH₃Si?O] to yield daughter siliconium ions. The [M-15]⁺ ion of sym-tetramethyldiphenyldisiloxane loses benzene, methane, dimethylsilanone and phenylmethylsilanone to yield daughter siliconium ions. The [M-15]⁺ ion of 1,1,3,3,5,5-hexamethyl-1,5-diphenyltrisiloxane loses benzene, tetramethylcyclodisiloxane and phenyltrimethylcyclodisiloxane to yield daughter siliconium ions. Finally, doubly charged ions are important in the mass spectra of the three series of aryl substituted di- and trisiloxanes discussed.     

Mass spectrometric study of isatins II. N-propyl(allyl,propargyl)isatins

The mass spectra of N-propyl- (I), N-allyl- (IV), and N-propargylisatin (VII) and their 5-methyl (II, V, VIII) and 7-methyl (III, VI, and IX) derivatives were recorded. It is shown that a portion of the [M-2CO]⁺ ions in the mass spectra of N-propargylisatins undergo rearrangement to give ions with a quinoline structure. A scheme for the fragmentation of the investigated compounds is presented. The mass spectra of the 5- and 7-methyl derivatives are compared.See [1] for communication I.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 5, pp. 639–641, May, 1977.     

Zum Mechanismus massenspektrometrischer Fragmentierungsreaktionen—IXSterische Effekte in den Massenspekten der Stereoisomeren von Decalin-2,3-diolen,Decalin-2,4-Diolen und Ihen Dimethyläthern

The mass spectra of all stereoisomers of decalin-2,3-diol, the corresponding dimethyl ethers and of some deuterated derivatives are discussed. The mass spectra of isomeric decalin-2,3-diols differ only slightly in ion intensities. The mass spectra of the stereoisomeric 2,3-dimethoxy-decalins are nearly identical within the series of transand cisderivatives. A mass spectrometric identification of the stereoisomers of these compounds is therefore diffucult. Stereoselective eliminations from the molecular ion are not observed. The mass spectra -of stereoisomeric decalin-1,4-diols show characteristic differences in the intensities of the[M ? H₂O]⁺˙-ions, which can be related to the geometry of the molecules in a similiar mode as was the case with cyclohexane-1,4-diols, The sterechemical control of the elimination of H₂O from the molecular ions has been confirmed by deuterium labelling. The mass spectra of stereoismeric 1,4-dimethoxy-decalins also differ characteristically in the intensities of the [M ? CH₃OH]⁺˙ ions. Furthermore peak due to the [M ? CH₂O]⁺˙ ions are only observed in the mass spectra of those stereoisomers, which have at least one conformation with a short distance between the two methoxy. The stereospecifity of the CH₃OH- and CH₂O-eliminationjs has also been determined by deuterium labelling.     

Study of adduct ions of meso-phenyl-substituted tetrabenzoporphyrins by fast-atom bombardment mass spectrometry

Mass spectra of meso-phenyl-substituted tetrabenzoporphyrins were investigated by fast-atom bombardment mass spectrometry and tandem mass spectrometry. A cluster of adduct ions with mass-to-charge ratio values higher than the corresponding molecular ions of the porphyrins has been observed. The mass number differences among the series of cluster ions are constant depending on the para-phenyl substituents. Under certain conditions, dimers or trimers of molecular ions with low abundances have been detected. To trace the origin of the adduct ions, a series of experiments based on mass spectrometry have been carried out. The mass spectrum of tetrabenzoporphyrin showed no adduct ions with mass number differences of 90 even with the addition of phenylacetic acid. The mass spectrum of meso-tetraphenylte-trabenzoporphyrin ¹³C-labeled at the meso carbons showed adduct ions with mass number differences of 91. Product spectra of [2M + H]⁺ or [3M + H]⁺ of porphyrins exhibited adduct ions. All these results suggest that fragmentations of [2M + H]⁺ or [3M + H]⁺ may be one of the many possible routes to form the adduct ions, and the mass number differences among the series of these cluster ions should correspond to the benzyl group from the meso positions of meso-phenyl-substituted tetrabenzoporphyrins.     

A mass spectrometric investigation on some 4,7-dioxo-4,5,6,7-tetrahydroindole derivatives

The mass spectrometric behaviour of a series of 2-aryl substituted 4,7-dioxo-4,5,6,7-tetrahydroindoles has been studied in different ionization conditions (Electron Ionization and Fast Atom Bombardment), with the aid of the metastable ion studies. In electron ionization conditions all the compounds exhibit a highly favoured, primary H₂ loss giving rise to the corresponding indole-4,7-diones; in the usual spectra no evidence for the molecular ions in the enolic form was found, while the OH* loss observed in the MIKE (mass analyzed ion kinetic energy) spectra of molecular ions suggests that species at low internal energy content isomerize to the corresponding tautomeric enolic form. FAB mass spectra show easy formation of an unusual [M + 2H]⁺ species, together with abundant [M + H]⁺ and M⁺ cations.     

Characterization of gem-difluoropropargyl synthons through HF loss from protonated molecules in methane chemical ionization mass spectra

Electron impact and methane chemical ionization mass spectra were obtained following gas chromatography/mass spectrometry for several gem-difluoropropargyl compounds, which had been synthesized as potential intermediates for synthesis of gem-difluoromethylene-containing C-3 acetylenes. EI spectra were variable with respect to the presentation of molecular ions, depending on substituent functional groups present. Methane-CI spectra were characterized by loss of 19 mass units from molecular weight with all compounds examined. These [M − 19]⁺ ions often presented as base peaks of the CI spectra, and were more reliably present and abundant than [M + 1]⁺ ions for these compounds. These ions could have been formed by elimination of HF from the protonated molecules under conditions of methane chemical ionization.     

The field desorption mass spectra of some oligosaccharides and their permethylates and peracetylates

Field desorption mass spectra have been obtained for a number of di-, tri- and tetrasaccharides, and for some permethyl and peracetyl derivatives. The free sugars usually show intense [M + 1]⁺ ions thus enabling the determination of molecular weights. The effect of variation of emitter current on the relative intensities of fragment ions has been investigated. Permethylated oligosaccharides show intense molecular ions; in contrast peracetylated oligosaccharides show only weak molecular ions but strong [M ? 60]⁺ ions. Information from electron-impact and field desorption mass spectra is essentially complementary.     

Chemical ionization of aliphatic nitro compounds

The chemical ionization mass spectra of various aliphatic nitro compounds have been studied. Almost all the nitro compounds form stable [M+H]⁺ ions in sharp contrast to the instability of their ions produced by other ionization techniques. The fragmentations of the [M+H]⁺ ions are discussed, the mechanisms and structures of fragment ions proposed being supported by quantum mechanical calculations. Correlations between chemical ionization mass spectra and structures of compounds studied are outlined. Reliable identification of mono- and polynitroalkanes and some related derivatives may be made by analysis of their chemical ionization mass spectra.     

Mass-spectrometric behavior of isomeric nitro- and nitroaminoindolizines and indoles

Peaks of [M — NO]⁺ and [M — NO₂]⁺ ions are characteristic for the mass spectra of nitroindolizines, whereas peaks of ions of the indole type, viz., [M — HCN]⁺ and [M- H,- HCN]⁺ (for alkylindoles), are not characteristic. In the mass spectra of nitroindoles the latter ions give more intense peaks, while the loss of a nitro group or its rearrangement is a considerably less significant process. When a dialkylamino group is introduced in the nitroindolizine molecule, the primary processes in the fragmentation of such compounds are due to fragmentation of the alkylamino group.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 6, pp. 765–768, June, 1982.     

Anomalous ions in the chemical ionization mass spectra of aromatic nitro and nitroso compounds

The appearance of [MH-30]⁺ ions in the chemical ionization mass spectra of aromatic nitro compounds may be due to their initial reduction to the corresponding amines within the ion source. Aromatic nitroso compounds may be similarly reduced to yield [MH-14]⁺ ions. The hydroxy derivatives of the nitroso compounds yield further anomalous ions at [MH-16]⁺ probably due to the reduction of the hydroxy groups.     

The mass spectra of halogenated β-sultones and a comparative study with vinyl methanesulfonates

The mass spectra of some halogenated β-sultones which have been determined show some common features. These include the absence of molecular or ions and the presence of abundant trihalomethyl and [M- trihalomethyl]⁺ ions. The latter can subsequently lose sulfur dioxide, ions are also observed in high abundance.     

Mass spectra of some quinoline hydroxamic acids and related compounds

The mass spectra of some 3- and 4-substituted quinoline hydroxamic acids and related compounds have been interpreted, and proposed fragmentations substantiated by means of deuterium-labeling and accurate mass determinations. All compounds examined gave abundant molecular ions; most showed strong [M ? 16]⁺ ions and weak [M ? 17]⁺ ions. The expulsion of CO and HCN molecules and H and HCO radicals were common subsequent decompositions. The spectrum of 4-hydroxy-2-methylquinazoline-3-oxide (VII) was unique and showed that nitric oxide was expelled from the molecular ion.     

Comparative study of [Xe]+ and [Ar]+ bombardment in secondary ion mass spectrometry for bioorganic compounds

Secondary ion mass spectra obtained by [Xe]⁺ bombardment are compared with those obtained by [Ar]⁺ bombardment. Although [Ar]⁺ ions are commonly used as primary ions in secondary ion mass spectrometry for organic compounds, [Xe]⁺ ions seem better as primary ions because they give a larger sputtering yield for a metal substrate than [Ar]⁺ ions. Cationized molecular intensities of sucrose, raffinose and stachyose, and quasimolecular ion intensities of tuftsin and eledoisin related peptide are investigated using [Xe]⁺ and [Ar]⁺ bombardments. The observed molecular species are 2–4 times more intense for [Xe]⁺ bombardment than for [Ar]⁺ bombardment, although the secondary ion mass spectra are almost the same in both cases.     

Ammonia Chemical Ionization Mass Spectra of Sydnones

The mass spectra of twenty-nine sydnones were measured by using NII₃ as a reagent gas. The [M + H + NH₃]⁺ ions are the base peaks for the entire series. Very few fragment ions were observed except for the derivatives of 4-hydroxymethylenesydnones (XXI-XXIX). Only the relatively stable sydnonyl-methylene cations are formed. With consistent formation of [M + 18]⁺ ion as the base peaks with simple spectra, the NH₃ CI-MS can be an excellent method for the molecular weight determination.     

Mass spectrometry of 3-substituted 4-hydroxyisoquinolines and their derivatives

Under electron impact, 3-aryl-4-hydroxyisoquinolines form [M – H]⁺, [M – CO]⁺ and [M – H – CO]⁺ ions with a subsequent elimination of HCN or CH₃CN. A cyclic structure for the [M – H]⁺ ion is suggested. The primary act of fragmentation of the corresponding methyle ether derivatives is the loss of CH₃?, as well as H?; the further fragmentatio is similar to that described above. It has been established that the unusual [M – H]⁺, [M – OH]⁺ and [M – CH₅?]⁺ ions are formed when 8 fragments. Fragmentation schemes for all compounds are proposed based upon high resolution mass spectra and deuterated analogues.     

The mass spectra of the trimethylsilyl esters of acetyl,schiff base and isothiocyanate derivatives of some aminoalkylphosphonic acids

Trimethylsilyl esters of acetyl, Schiff base and isothiocyanate derivatives of a series of aminoalkylphosphonic acids were prepared for the purpose of characterizing these phosphorus compounds by combined gas chromatography and mass spectrometry. The mass spectra of these derivatives were investigated by means of high resolution mass measurments and deuterium labeling. Ions characteristic of the presence of the trimethylsilylphosnate group were observed at m/e 121, 195, 211 and 225 to 227 in the spectra of all the derivatives. Several ions produced by interaction between the trimethylsilyl group and the derivatized amino function were present, particularly in the spectra of the acetate derivatives ([M — 56]⁺, [M — R]⁺ and [M — 153]⁺, where R is the side chain attached to C-1), and the isothiocynate derivatives (m/e 268, 253, 241, 190 and 116).     

The mass spectra of intramolecularly hydrogen bonded 2(1H)-quinoxalinone and 2H-1,4-benzoxazin-2-one

The mass spectra of those 3-phenacyl derivatives of 2(1H)-quinoxalinone and 2H-1,4-benzoxazin-2-one with an intramolecular hydrogen bonding showd that: (1) the primary elimination of the shole sidchain is reduced as compared with an unchelated derivative; (2) the importan t fragmentation routes in the quinoxalinone series are ring cleavage with loss of CO followed by recyclization and expulsion of a hydrogen atom, and this can also occur in the reverse order; (3) this reverse process is virtually absent in the benzoxazinone series. Finally, the doubly charged molecular ions appear to undergo an analogous decomposition giving fairly intense [M-CO]²⁺ or [M-(CO+H or CI]²⁺ ions.     

Electron impact ionization mass spectrometry and tandem mass spectrometry of phenylalkylpyridazines

The mass spectrometric fragmentation behaviour of pyridazine and four monosubstituted derivatives containing a pbenylalkyl side-chain (3- and 4-benizylpyridazine, 3- and 4-(2-pbenylethyl)pyridazine) was investigated. In the electron impact ionization mess spectra of the 3-substituted compounds abundant [M – H]⁺ peaks are observed. This allows a clear distinction between 3- and 4-substituted pyridazines, as the spectra of the latter isomers show only very weak [M – H]⁺ signals. The stability of [M – H]⁺ ions derived from 3-alkylpyridazines (deduced from only the very low abundance of further fragment ions) gives strong evidence for a cyclic structure of these ions. One fragmentation pathway typical of the parent pyridazine, the [M - N₂] fragmentation, was not detectable with any of the phenylalkylpyridazines investigated. Instead, loss of HCN, H₃CN⁺ and N²H⁺ was observed. An interesting fragmentation, observed with 3-(2-phenylethyl)pyridazine, is the loss of ⁺CH₃ from the molecular ion and also from the [M – H]⁺ ion.     

Fast atom bombardment (FAB) mass spectrometry of piperidine N-oxide derivatives and free radical quenching under FAB conditions

Mechanisms are proposed for the formation of M⁺, [M + 2H]⁺ and [M + 3H]⁺ ions in the fast atom bombardment (FAB) mass spectra of 4-(2,2,6,6-tetramethyl-1-oxyl)-piperidol and its carboxylates. Free radical quenching induced by the fast atom beam has been observed. The effects of temperature on the radical quenching and of acid on the FAB mass spectra are discussed. The experiment showed that the volatile liquid samples with vapour pressures higher than that for glycerol produced M⁺ even-electron molecular ions, and the FAB mass spectra were similar to the corresponding electron ionization mass spectra. For the solid samples, it was found that the free radicals were quenched during the FAB process so that the mononitroxide and dinitroxide compounds produced [M + 2H]⁺ and [M + 3H]⁺ ions, respectively. Further experiments showed that the intensities and stabilities of [M + 2H]⁺ and [M + 3H]⁺ ions could be improved by addition of acids.     

Mass-spectrometric study of methyl-substituted azomethines of the 4-azafluorene series

The M⁺ and [M-H]⁺ ion peaks are the peaks of maximum intensity in the mass spectra of Schiff bases belonging to the 4-aza-9-fluorenylidenearylamine series. The dependence of the relative intensity of the [M-H]⁺ fragment on the structures of the I–XI molecules provides evidence for the possibility of the occurrence of rearrangement processes involving the formation of this ion. The formation of [M-CH₃]⁺, [M-HCN]⁺, [M-Ar]⁺, and [M-CNAr]⁺ ions is also characteristic for the fragmentation of the investigated compounds. It was found that, in contrast to other types of Schiff bases, the ejection of an HCN molecule during the mass-spectrometric fragmentation of the investigated compounds occurs without participation of the nitrogen atom of the azomethine group. The elimination of a CNAr particle by the molecular ions is a distinctive feature of the investigated series of Schiff bases.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 3, pp. 397–402, March, 1979.