Tetraalkylammonium cations in electron impact mass spectrometry

Twenty-five tetraalkylammonium halide salts were investigated by means of electron impact mass spectrometry. In all cases, corresponding ammonium cations have been detected at low electron energy. Moreover, [C+M]⁺ have been detected (where C and M denote ammonium cation and molecule, respectively) for both symmetrical salts and iodine salts. Quaternary ammonium salts are considered to be more stable than believed previously.     

In-beam electron impact mass spectrometry of aliphatic alcohols

The characteristics of the in-beam electron impact mass spectra of six isomers of undecanol as well as several 1-alkanols have been examined. In addition to the characteristic ions observed in the conventional electron impact spectra, the [2M+1]⁺, [2M+1-H₂O]⁺, [2M+1-2H₂O]⁺, [2M-R or R′]⁺, [2M-H₂O? R or R′]⁺, [2M? 2H₂O? R or R′]⁺ and [M+1? H₂O]⁺ peaks are common in the in-beam electron impact mass spectra of the undecanol isomers of structure RCH(OH)R′. Deuterium labelling experiments have shown that the extra proton in the protonated dimer ions, [2M+1]⁺, originates from the hydroxy group. The processes which produce the important peaks in the high m/e regions are discussed.     

Ion-trap detector electron impact mass spectrometry: Practical considerations

An investigation of the quality of mass spectra obtainable by the Finnigan ion-trap detector (ITD) and on how this quality may depend on sample size is described. For compounds which are not very thermolabile or too prone to fragmentation, near-normal spectra can be expected if the sample sizes do not exceed amounts of the order of 100 ng. Analyte loads which generate acceptable total ion current chromatograms with narrow-bore capillary columns (about 500 ng) could still produce ITD mass spectra having enhanced quasi-molecular ions, [M + 1]⁺, abnormal distributions of peak intensities and unusual fragments. Even under optimum conditions, certain analytes, e.g. acyclic alkanes, n-alkanols and pyridines, will manifest spectral characteristics which are strictly typical of the ITD. In favourable cases, the formation of quasi-molecular ions can be exploited for relative molecular mass determination. Even under conditions of self-chemical ionization, the ITD spectra of most analytes generally retain enough electron impact mass spectral character to be readily recognizable by inspection or by library algorithms.     

Fragmentation pathways of isomeric dodecenols studied by electron impact mass spectrometry

Electron impact-induced fragmentations of isomeric dodecen-1-ols were investigated using mass-analysed ion kinetic energy (MIKE) spectrometry and high-resolution data. The principal fragmentation pathways of the positional isomers studied are dominated by the C?C double bond and involve migration and radical-site rearrangements along the carbon chain with the aid of consecutive rearrangements of hydrogen atoms.     

A study on electron impact mass spectrometry of epoxy methylated fullerenols

Mass spectra of the epoxy methylated[60]fullerenols were obtained by EI mass spectrometry using "desorption" or "in-beam" technique. The mass spectra have an intense molecular monocation peak M(+) and a weak dication peak M(++), revealing the stability of these products under the MS (EI) conditions. The remaining peaks correspond to the successive loss of methyl groups and oxygen atoms for which the pure fullerene represents a more stable product. The distinction between the multiply charged fullerene C(60)(z+) and their fragments with equal m/z was also studied.     

Chemical ionization and electron impact mass spectrometry of some organophosphonate compounds

The application of gas chromatography chemical ionization mass spectrometry to the determination of a variety of alkyl alkylphosphonates, phosphonofluoridates, phosphonothiolates and an amidophosphorocyanidate is described. Comparison is made between the electron ionization and chemical ionization mass spectrometry of these compounds. Chemical ionization mass spectrometry is shown to enhance the capability for identification, especially when a limited sample is available. Results indicate that methane is highly useful for obtaining protonated molecular ions and association ions (formed by the transfer of a reactant ion to a sample molecule) as well as meaningful fragment ions. Ionizing ethylene and isobutane gives protonated molecular ions as base peaks for all of the compounds studied, including those where a lower abundance of the [MH]₊ ion is found via methane chemical ionization mass spectrometry. Ethylene is superior to isobutane on the basis of its effectiveness for serving as both a carrier and a reagent gas and gives better sensitivity. Although not an intrinsic part of this present study, analytical sensitivities in the subnanogram range were found.     

Alkylation in electron impact mass spectrometry of hydrobromides of 2-alkylthioorotic acids

The mass spectral fragmentations of eight 2-alkylthioorotic acids and their hydrobromides were investigated. Fragmentation pathways, the elucidation of which was assisted by accurate mass measurements and metastable transitions, are proposed. It was found that there is evidence in the electron impact mass spectra of the hydrobromides of 2-alkylthioorotic acids of intermolecular transfer of an alkyl group.     

Analysis of sodium alkylsulphonates using filament heated in-beam electron impact mass spectrometry

Summary By means of the filament heated in-beam method at 280–450° C, the series of sodium alkylsulphonates (RSO₃Na, where R=C₂H₅ to n-C₁₂H₂₅) give very simple mass spectra: Na⁺, [RSO₃Na₂]⁺, which is the base peak except for R=n-C₄H₉, [(RSO₃)₂Na₃]⁺ and, in most cases, [(RSO₃)₃Na₄]⁺. Fragmentations other than these three or four peaks are observed only in the case of n-heptylsulphonate. The proposed method of analysis for simple alkylsulphonic acids is applicable to ordinary electron-impact mass spectrometers.

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Analyse von Natrium-alkylsulfonaten durch Elektronenstoß-Massenspektrometrie mit Probenerhitzung im Elektronenstrahl

Zusammenfassung Mit Hilfe dieser Methode (280–450° C) erhält man für Natriumalkylsulfonate (RSO₃Na mit R=C₂H₅ bis n-C₁₂H₂₅) sehr einfache Massenspektren: Na⁺, [RSO₃Na₂]⁺ (Basispeak mit Ausnahme von R=n-C₄H₉), [(RSO₃)₂Na₃]⁺ und in den meisten Fällen [(RSO₃)₃Na₄]⁺. Andere Fragmentierungen als diese 3 oder 4 Peaks wurden nur bei n-Heptylsulfonat beobachtet. Dieses Verfahren zur Analyse einfacher Alkylsulfonsäuren ist für übliche Elektronenstoß-Massenspektrometer verwendbar.

     

Analysis of ten novel rhenium complexes by desorption chemical ionization mass spectrometry

The desorption chemical ionization (DCI) mass spectrometry of ten rhenium compounds is compared to the desorption electron impact (DEI) mass spectrometry of the same compounds. Using 10% ammonia in nitrogen as the reagent gas, the DCI mass spectrometric (MS) technique provided [M + H]⁺ ions for each rhenium compound. In most cases, the DEIMS method provided only fragment ions.     

Electrospray mass spectrometry and tandem mass spectrometry of bimetallic oxovanadium complexes

A series of six bimetallic oxovanadium complexes (1-6; only one was purified) were investigated by electrospray quadrupole time-of-flight tandem mass spectrometry (ESI-QTOF-MS/MS) in negative-ion mode. Radical molecular anions [M](.-) were observed in MS mode. Fragmentation patterns of [M](.-) were proposed, and elemental compositions of most of the product ions were confirmed on the basis of the high-resolution ESI-CID-MS/MS spectra. A complicated series of low-abundance product ions similar to electron impact (EI) ionization spectra indicated the radical character of the precursor ions. Fragment ions at m/z 214, 200, and 182 seem to be the characteristic ions of bimetallic oxovanadium complexes. These ions implied the presence of a V-O-V bridge bond, which might contribute to stabilization of the radical. To obtain more information for structural elucidation, three representative bimetallic oxovanadium complexes (1-3) were analyzed further by MS in positive-ion mode. Positive-ion ESI-MS produced adduct ions of [M + H](+), [M + Na](+), and [M + K](+). The fragmentation patterns of [M + Na](+) were different than those of radical molecular anions [M](.-). Relatively simple fragmentation occurred for [M + Na](+), possibly due to even-electron ion character. Negative-ion MS and MS/MS spectra of the hydrolysis product of Complex 1 supported these finding, in particular, the existence of a V-O-V bridge bond.     

An unusual HgCl rearrangement in electron impact mass spectrometry of some halomercurioalkyl derivatives

The electron impact mass spectrometric behaviour of three 2-methyl-2-chloromercuriomethyl-2,6-dihydro-5H-pyrano[3,2-c]quinolin-5-ones have been studied in detail with the aid of metastable ion data. The primary loss of C₄H₇, necessarily involving an unusual HgCl rearrangement, is discussed and justified by the formation of a thermodinamically stable Hg-containing cyclic structure.     

Comparison of electron impact and chemical ionization mass spectra of some arenetricarbonylchromium complexes

The mass spectrometric behavior of a) the tricarbonylchromium complexes of a series of aromatic hydrocarbons, b) the dimethyldiphenyl compounds of the Group IV elements (i.e., diphenylpropane, dimethyldiphenylsilane, etc.) and c) the mono- and bis-tricarbonylchromium complexes of these ligands under electron impact and chemical ionization conditions are reported. The MH⁺ ion is base peak for all of the simple arenetricarbonylchromium complexes using chemical ionization, whereas [M — 3 CO]⁺ or ⁵²Cr⁺ dominate the spectra with electron impact ionization. The chemical ionization spectra of the series of Group IV element ligands do not exhibit signals in the molecular ion region, the base peak being [M — Ph]⁺. [M — CH₃]⁺ is the electron impact base peak for each of the ligands except the lead-containing compound, for which the base peak is ²⁰⁸Pb⁺. The mono-tricarbonylchromium complexes yield chemical ionization molecular ion clusters, but their base peaks arise via fragmentation of the Group IV element—aromatic ring bonds. Electron impact ionization spectra of the mono complexes are characterized by losses of CO and the production of Cr⁺ ions, neither of which occurs with chemical ionization. For the series of bis-tricarbonylchromium complexes, an MH⁺ ion is prominent only in the chemical ionization spectrum of the diphenylpropane complex. The electron impact induced spectra of the bis-tricarbonylchromium complexes are similar to those of the mono-complexes in that loss of CO is a prominent feature.     

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.     

Retrosynthetic reactions in mass spectrometry. Deacylation of ortho phthalamic acids under electron impact

Ortho Phthalamic acids under electron impact show a retrosynthetic reaction leading to both phthalic anhydride and amine complementary ions, the corresponding neutrals of which are the usual synthetic precursors of the original compounds. The single case of a primary amine derivative is examined, which shows the formation of [M? H₂O]^+˙ ions having the structure of the related N-substituted imide, by a process which parallels a well known thermal reaction. It also gives the species [C₈H₆NO₂]⁺ (of the same nominal mass as phthalic anhydride), the structure of which is still under study. Ionic structures are supported by collision induced mass analyzed ion kinetic energy spectra.     

“In beam” electron impact mass spectrometry: the structure of a bacteriochlorophyll allomer

By means of proton n.m.r and “in beam]rd electron impact mass spectrometry, an allomer of bacteriochlorophyll is shown to be hydroxylated in ring V.     

Construction of spiro-oxaquinolizidinone framework of Upenamide via organoiron complexes

An organoiron approach toward the synthesis of an elaborated tricyclic spiro-oxaquinolizidinone ring has been accomplished. The key intermediate was efficiently prepared through a nitrile addition to the appropriately functionalized cyclohexadienylium-Fe(CO)₃ perchlorate salt to install the requisite quaternary center in the spiro-oxaquinolizidinone ring.     

A novel approach to synthesis of the cinnoline ring system via organoiron(cyclopentadienyl) complexes

An efficient synthesis of 3-mono or 3,4-disubstituted cinnolines from (o-dichlorobenzene)(cyclopentadienyl)iron hexafluorophosphate in three or four steps has been achieved. o-Chlorophenyl-alkyl or alkylaryl ketone complexes obtained from the o-dichlorobenzene complex upon treatment with enolate anions, react with hydrazine forming 3-mono or 3,4-disubstituted 1,4-dihydrocinnoline complexes. Treatment of the later with sodium amide leads to an aromatization-demetallation reaction resulting in formation of cinnolines, i.e. 3-methyl-, 3-phenyl- and 3,4-dimethylcinnoline. The influence of substituents bonded to the carbon atom adjacent to the complexed benzene ring in o-chlorophenyl -alkyl or -alkylaryl ketone prior to cyclization on the cyclization reaction is discussed.     

Electron impact mass spectrometry of some naphthoxypolymethylenethiopyrimidines

The electron impact induced fragmentation of a large number of 2- and 4-S-(2-naphthoxy)-polymethyienethiouracils is discussed in detail, with the aid of exact mass measurements and observation of metastable decompositions. The 2- and 4-thiopyrimidine structures can be easily distinguished by their mass spectra.     

Electron impact mass spectrometry of praziquantel derivatives

The electron impact mass spectra of a series of compounds related to the anthelmintic substance praziquantel are described in sufficient detail to permit their assay in biological samples by selected ion monitoring.