Fragmentation of symmetrically substituted methylferrocenes under electron impact

Mass spectra of a series of individual methylferrocenes (Me_nC₅H_5?n)₂Fe (where n = 1–5) are reported. The manner of fragmentation of these compounds is discussed.     

Fragmentation selectivity in electron impact ionization mass spectra of substituted dimethoxybenzenes

Several 1-X-sabstitirted-3-methoxy-4-trideuteromethoxybenzens were synthesized and their electron impact ionization mass spectra were measured with an ionizing energy of 20 eV. From the peak intensity ratio of [M ? CD₃ ] and [M ? CH₃] the fragmentation-directing ability of the substituent X was evaluated. The most powerful group was found to be NH₂, which expelled a methoxy methyl group only from its para position. The CH₃ group and four halogen atoms, F, Cl, Br and I, exerted a moderate effect Electron-withdrawing groups such as NO₂, CHO and CN had only a little influence on the fragmentation selectivity. These results were interpreted in terms of the effect of X on the distribution of both the unpaired electron and the positive charge in the molecular ion.     

Polyfluorocyloalkenes Part XI Perfluoro - bicyclo(3,3,0) oct-7(8)-ene, - bicyclo(4,3,0)-non-8(9)-ene and - bicyclo (4,4,0)-dec-9(10)-ene and some derivatives

Tetradecafluorobicyclo (4,3,0) non-8(9)-ene has been prepared by cobaltic fluoride fluorination of decafluoro indane. The reactivities of the double bonds in dodecafluorobicyclo (3,3,0) oct-7(8)-ene and hexadecafluorobicyclo (4,4,0) dec-9(10)-ene have been studied qualitatively by the use of chlorine, methanol, cobaltic fluoride, ammonia and dimethylamine and the derivatives so obtained have been characterised.     

Fragmentation of substituted 2-sila-1,3-dioxacycloalkanes under electron impact

The mass spectrometric dissociation of 2-sila-1,3-dioxacycloalkanes takes place mainly with loss of the substituent from position 2 of the heterocycle. The fragment formed here eliminates the molecular of carbonyl compounds or alkenes.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 2, pp. 272–275, February, 1986.     

Fragmentation of pyrazolecarbaldehyde thio- and dithioacetals under electron impact and chemical ionization

The mass spectra of 1-substituted 3,5-dimethyl-1H-pyrazole-4-carbaldehyde bis(2-hydroxyethyl) dithioacetals and thioacetals were studied for the first time. The main fragmentation pathways of their molecular ions generated under electron impact and chemical ionization were similar. Primary decomposition of the molecular ions of bis(2-hydroxyethyl) dithioacetals involves elimination of 2-sulfanylethanol molecule with formation of the corresponding 1,3-oxathiolane radical cation. Fragmentation of the molecular ions [M]⁺ · and [M + H]⁺ derived from 2-(3,5-dimethyl-1H-pyrazol-4-yl)-1,4,6-oxadithiocanes includes cleavage of the eight-membered heteroring and elimination of C₄H₉OS ·. Substituents in the heteroring of pyrazolecarbaldehydes inhibit decomposition processes related to the aldehyde group.     

Reactions of 14-hydroxy-14-azadispiro[5.1.5.2]pentadec-9-ene-7,15-dione and related compounds. II

3 When 11-diethyl- and 3, 11-di-n-propyl-14-hydroxy-14-azadispiro[5.1. 5.2]pentadec-9-ene-7, 15-dione (E-IV and n-Pr-IV) are heated with polyphosphoric acid at 55–65°, the 14-hydroxyl group cyclizes at the 11-carbon to form E-VI and n-Pr-VI, the structures of which have been established. Compounds P-IV, i-Pr-IV and t-B-IV do not cyclize under these conditions. The Beckmann rearrangement of 12-hydroxy-12-azadispiro[4.1.4.2]tridec-8-ene-6, 13-dione-6-oxime (P-I) with polyphosphoric acid at 40–50° formed only the normal product, P-II, which could not be cyclized. Compound P-IV was the only ketone of this series which would add hydrogen cyanide to form a cyanohydrin.     

Syntheses of 11-hydroxy and 11-hydroxy-11-methyl-14-methoxy-14-azadispiro[5.1.5.2]pentadec-9-ene-7,15-diones

A facile synthesis, which permits regioselective incorporation of hydroxy and/or methyl substituents at position 11 of 14-methoxy-14-azadispiro[5.1.5.2]pentadec-9-ene-7,15-dione, has been described.     

Fragmentation of 3,7-dialkyl-1,5-diphenyl-3,7-diazabicyclo[3.3. 1]nonan-9-ones under electron ionization

A series of 3,7-dialkyl-1,5-diphenyl-3,7-diazabicyclo[3.3. 1]nonan-9-ones was prepared, and the details of their fragmentation under electron ionization (EI) were elucidated. The molecular ions of each compound under consideration were quite abundant in their EI spectra. Full-scan spectra exhibited a number of fragment ions which were clearly assigned using MS/MS and accurate mass measurements. The basic fragmentation of 3,7-dialkyl-1,5-diphenylbispidinones was due to the cleavage of C(1)-C(2) bond followed by a hydrogen migration similar to an odd-electron McLafferty rearrangement. Alternatively, the C(1)-C(2) bond cleavage was followed by the elimination of an imine molecule, Alk-N=CH(2). Further fragmentation resulted in ions at m/z 234 and 103, present in the spectra of all the compounds under study. The fragmentation pathways proposed in this paper are based on the substituent shifts, accurate mass measurements and collision-induced dissociation spectra of selected ions. The results of the present work can be useful in selecting the fragment ions suitable for identification and quantitation of bispidinones in biological matrices.     

Fragmentation of substituted 4-hydroxy-2-quinolones under the influence of electron impact

The general principles of the mass-spectral disintegration of 4-hydroxy-2-quinoline derivatives containing various substituents attached to the nitrogen in the 3 position were established. It was found that the disintegration of 4-hydroxy-2-quinolone and its N-substituted derivatives proceeds primarily through cleavage of the heterocyclic ring, while the principal pathways of the disintegration of 3-acyl derivatives are associated with fragmentation of the acyl group.     

Differentiation of diastereomeric conduramine derivatives under electron ionization and chemical ionization mass spectral conditions

Diastereomeric conduramine derivatives, i.e., (1R,2S,3R/S,6S)-6-(N-carbomethoxyamino) 1,2-O-isopropylidenecyclohex-4-ene-1,2,3-triol (1 and 2) and their O-acetyl derivatives (3 and 4), were studied using gas chromatography (GC) with electron ionization (EI) and chemical ionization (CI). The EI mass spectra of diastereomeric pairs show consistent differences in the relative abundances of characteristic ions. The EI fragmentation patterns are based on precursor/product ion spectra, high-resolution mass spectrometry (HRMS) and deuterium labelling. The CI spectra show differences from the EI spectra, and the isobutane/CI spectra are much simpler than the methane/CI spectra. The differences shown in the CI spectra are similar to those shown in the product ion spectra of [M+H](+) ions generated under electrospray ionization (ESI) conditions. Theoretical calculations are performed to understand the observed differences. The differences in the relative stabilities of molecular ions, or protonated molecules at different sites, can explain the observed differences in the spectra.     

Fragmentation and rearrangement reactions in certain 1,2,3-triaryl-2-propen-1-ones following electron impact and chemical ionization

The electron impact (EI) and chemical ionization (CI) mass spectra of certain 1,2,3-triaryl-2-propen-1-ones (TAPs) have been studied in detail with the help of exact mass measurements, deuterium labelling and metastable data. The E- and Z-isomeric pairs do not show any difference in their behaviour under EI or CH₄ CI conditions. EI-induced rearangement reactions in the TAPs include aryl migration to carbonium ion centres. A study of the metastable transitions reveals aryl group interchange in the molecular ions prior to fragmentation. Under EI conditions loss of arene involves either C(2) or C(3) aryl groups while under CI conditions the C(1) aryl is lost as a neutral arene molecule. Mechanisms for the different fragmentation modes are given.     

Fragmentation patterns of novel dithiocarbamate derivatives with pharmaceutical activity under electrospray ionization tandem mass spectrometry conditions

The fragmentation patterns of a novel series of dithiocarbamate derivatives with pharmaceutical activity were investigated by positive ion electrospray ionization mass spectrometry in conjunction with tandem mass spectrometry (ESI-MS(n)). In the gas phase, the dithiocarbamate protonated molecules containing the piperazinium moiety undergo losses of bromide to form the piperazinium cation by ionization, followed by subsequent losses of methyl bromide, ring opening and rearrangement of piperazinium. Furthermore, the dithiocarbamate derivatives and their intermediates both undergo cleavage of the C-S bond to produce two common fragment ions. The different fragmentation observed for these compounds facilitated their identification and could be valuable in the further study of their metabolic pathways as prodrugs.     

Differentiation of isomeric substituted diaryl ethers by electron ionization and chemical ionization mass spectrometry

A series of isomeric substituted diaryl ethers, i.e., 2- or 4-NO2, 5- FC6H3OC6H4 (4-R), where R=H, COCH3, COOCH3, NO2, CHO, OCH3 etc., which comprise ortho and para isomers with respect to the position of the nitro group are studied under GC-EI-MS and CI-MS conditions. The EI mass spectra of ortho and para isomers show distinct fragment ions, where the [MOH]+ and [MOHO]+ ions specifically appeared in all spectra of the ortho isomers (I), whereas the para isomers (II) contain [MO]+ and [MNO]+ ions. The [MOHCO]+ and [MOHNO]+ ions in I, and [MNO2]+ ion in II are the other specific fragment ions observed but feasibility of these fragment ions are found to depend on the nature of the substituent (R). The substitution (R) effect is also clearly reflected in the formation of fragment ions due to sigma-cleavage process with or without hydrogen migration. Similar differences in the formation of specific fragment ions are also observed in ortho and para isomers of substituted aryl naphthyl ethers. The methane/CI of isomeric compounds resulted in the same set of fragment ions, but prominent differences are observed in the relative abundance of [MHNO]+, which is relatively higher in para isomers compared with corresponding ortho isomer.     

Fragmentation by electron impact ionization and intracluster reactions of size selected (N2H4) n and (OCS) n clusters

The hydrogen-bonded (N₂H₄) _n clusters and the van der Waals (OCS) _n clusters are size selected in a scattering experiment with a He beam up to the cluster sizen=6. By measuring the angular distributions of the scattered clusters the complete fragmentation pattern of electron impact ionization is obtained. For Hydrazine the two main fragment masses are the protonated species (N₂H₄) _n?1H⁺ and with somewhat weaker intensities also the nominal ion mass (N₂H₄) _n ⁺ . The largest intensity is observed for the monomer ion N₂H ₄ ⁺ to which clusters up ton=5 fragment. For carbonylsulfide, completely different results are obtained. Aside from the fragments of the OCS monomer and the van der Waals cluster fragments (OCS) ₂ ⁺ and (OCS) ₃ ⁺ signals at mass S ₂ ⁺ , S ₃ ⁺ and S₂OCS⁺ are detected. This indicates a fast chemical reaction in the cluster according to: S + OCS → CO + S₂ which occurs for clusters of sizen ≥ 2. Peaks at S ₃ ⁺ and S₂OCS⁺ are seen for the first time forn ≥ 5 according to a further reaction of S₂ in the cluster.