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1.
The metastable ion supported fragmentation process in the mass spectra of the cyclohexadienyl derivative C6H7Mn(CO)3, the cycloheptadienyl derivative C7H9Mn(CO)3, the 1,2,3,4,5-and 1,2,3,5,6-pentahaptocyclootadienyl derivatives C8H11Mn(CO)3, the cyclooctatrienyl derivative C8H9Mn(CO)3 and the substituted cyclopentadienyl derivative (CH3)2NCH2C5H4Mn(CO)3, are described. Losses of carbonyl groups, generally stepwise, from the molecular ions to give the corresponding [M – 3CO]+· ions are first observed. Further fragmentation of the carbonyl-free [M – 3CO]+· ions can involve a variety of processes such as the following: (a) elimination of a neutral manganese atom to give a hydrocarbon fragment; (b) elimination of a neutral hydrocarbon fragment to give an [MnH]+· ion; (c) dehydrogenation; (d) elimination of a 2-carbon C2H2 or C2H4 fragment; (e) elimination of a C3H4 or C3H6 fragment as a neutral species when it is bridging two carbon atoms bonded to manganese, as in C8H9Mn(CO)3 and 1,2,3,4,5,h5-C8H11Mn(CO)3, respectively. Fragmentation of the [M – 3CO]+· ion in (CH3)2NCH2C5H4Mn(CO)3 presents the following additional features: (a) elimination of C6H6 with a nitrogen shift from carbon to manganese; (b) elimination of a neutral dimethylamino fragment to give [C6H6Mn]+·, which then loses neutral C6H6, C6H5 or Mn fragments and thus is formulated tentatively as [(fulvene)Mn]+· or [C6H5MnH]+· rather than [(benzene)Mn]+·.  相似文献   

2.
The structures of gas-phase [C4H6O] radical cations and their daughter ions of composition [C2H2O] and [C3H6] were investigated by using collisionally activated dissociation, metastable ion measurement, kinetic energy release and collisional ionization tandem mass spectrometric techniques. Electron ionization (70 eV) of ethoxyacetylene, methyl vinyl ketone, crotonaldehyde and 1-methoxyallene yields stable [C4H6O] ions, whereas the cyclic C4H6O compounds undergo ring opening to stable distonic ions. The structures of [C2H3O] ions produced by 70-eV ionization of several C4H6O compounds are identical with that of the ketene radical cation. The [C3H6] ions generated from crotonaldehyde, methacrylaldehyde, and cyclopropanecarboxaldehyde have structures similar to that of the propene radical cations, whereas those ions generated from the remainder of the [C4H6O] ions studied here produced a mixed population of cyclopropane and propene radical cations.  相似文献   

3.
The appearance potentials for the transition ([HNCO]→ [HCO]+ + N), determined for the reaction in the ion source and in the first field free region (15·84 and 15·52 eV) correspond, respectively, to the vertical and adiabatic third ionisation potential of HNCO, as determined by photoelectron spectroscopy. The formyl ion and nitrogen radical are formed in the ground state, which requires predissociation of a quartet molecular ion of HNCO. A heat of formation δHf(HNCO)g = ?25 ± 3 kcal mol·1 was determined from the appearance potential and kinetic energy release for the metastable ion [HCO]+, and from the difference in appearance potentials for the ion [NH]+· produced from the isoelectronic molecules HNCO and HN3.  相似文献   

4.
Metastable ion peak shapes, dimensions and relative abundances have been measured for the three fragmentations [C3H6]+· → [C3H4]+· + H2, [C3H6]+· → [C3H5]+ + H· and [C3H6]+· → [C3H3]+ + H2 + H·. [C3H6]+· ions were derived from propene, cyclopropane, tetrahydrofuran, cyclohexanone, 2-methyl but-1-ene and cis-pent-2-ene. Activation energies for these fragmentations have been evaluated. Three daughter ion dissociations ([C3H5]+ → [C3H3]+ + H2, [C3H5]+ → [C3H4]+· + H· and [C3H4]+· → [C3H3]+ + H·) have been similarly examined. Ion structures have been determined and the metastable energy releases have been correlated with the thermochemical data. It is concluded that the molecular ions of propene and cyclopropane become structurally indistinguishable prior to fragmentation and that differences in their metastable ion characteristics can be ascribed wholly to internal energy differences; the latter can be correlated with the photoelectron spectra of the isomers. The pathway for the consecutive fragmentation which generates the metastable ion peak (m/e 42 → m/e.39) has been shown to be It is likewise concluded that fragmentating [C3H6]+· ions generated from the various precursor molecules are also structurally indistinguishable and cannot be classified with either molecular ion of the isomeric C3H6 hydrocarbons.  相似文献   

5.
Breakdown graphs have been constructed from charge exchange data for the epimeric 2-methyl-, 3-methyl- and 4-methyl-cyclohexanols. Although the breakdown graphs for epimeric pairs are essentially identical above ~12 eV recombination energy, significant differences are observed for the epimeric 2-methyl- and 4-methyl-cyclohexanols at low internal energies. For the 2-methylcyclohexanols the ratio ([M? H2O]/[M])cis/([M? H2O]/[M])trans is 3.2 in the [C6F6] charge exchange mass spectra. This is attributed to both energetic and conformational effects which favour the stereospecific cis-1,4-H2O elimination for the cis epimer. The breakdown graph for trans-4-methylcyclohexanol shows a sharp peak in the abundance of the [M? H2O] ion at ~10 eV recombination energy which is absent from the breakdown graph for the cis epimer. This peak is attributed to the stereospecific cis-1,4-elimination of water from the molecular ion of the trans isomer; the reaction appears to have a low critical energy but a very unfavourable frequency factor, and alternative modes of water loss common to both epimers are observed at higher energies. As a result, in the [C6F6] charge exchange mass spectra the ([M? H2O]/[M])trans/([M? H2O]/[M])cis ratio is ~24, compared to the value of 13 observed in the 70 eV EI mass spectra. No differences are observed in either the metastable ion abundances or the associated kinetic energy releases for epimeric molecules.  相似文献   

6.
The major metal-containing species formed upon fast atom bombardment of amino acid/Ni+2 mixtures is the [M + Ni]+ adduct, involving reduction of the Ni+2 to the +1 oxidation state. By contrast, electrospray ionization of amino acid/Ni+2 mixtures produces predominantly [Ni(M ? H)M]+; this species, on collisional activation, produces predominantly [M + Ni]+ by elimination of [M - H], presumably a carboxylate radical. The unimolecular fragmentation reactions occurring on the metastable ion time scale for the [M + Ni]+ adducts of a variety of α-amino acids have been recorded. The adducts with phenylalanine, α-aminoisobutyric acid and α-aminobutyric acid fragment by elimination of H2O, H2O + CO and, to a minor extent, by elimination of CO2. These reactions are similar to those observed for the [M + Cu]+ adducts of α-amino acids. A reaction distinctive for the [M + Ni]+ adducts involves formation of the immonium ion RCH=NH 2 + . By contrast, the [M + Ni]+ adducts with leucine, isoleucine, and norleucine show extensive metastable ion fragmentation by elimination of H2, CH4, C2H4, C3H6, and C4H8, with the relative importance of the different fragmentation channels depending on the configuration of the C4H9 side chain. These results are interpreted in terms of C-C and C-H bond activation of the C4H9 side chain by the Ni+. The adducts with valine and norvaline fragment in a fashion similar to the adduct with phenylalanine, except that minor elimination of C3H6 is observed.  相似文献   

7.
The ratio [M ? D]/{[M-D] + [M ? H]} in the 70 eV mass spectra of six deuterated 3-methylthiophenes has been determined. From these values the mole fractions of the molecular ions that lose hydrogen atoms specifically from the various positions of the molecule were calculated, as well as the mole fraction in which the hydrogen atoms are fully scrambled before hydrogen elimination. It appears that hydrogen atoms are mainly lost from a fully scrambled [C5H6S]+· ion and from the α-position of the original molecular ion. A deuterium isotope effect of 1·60 to 1·72 was calculated for the hydrogen elimination. The reaction was also studied at low electron energies. In order to determine the degree of scrambling in the [C5H5S]+ ions, some decomposition reactions of this ion were investigated.  相似文献   

8.
In order to establish the mechanism of CO loss occurring during metastable decomposition of protonated 1-indanone, fragmentations of monocyclic [C9H9O]+ isomers have been studied. These ions of known structure were prepared by CI protonation and fragmentation of the corresponding acids chlorides. It is demonstrated that the wide component of the [MH? CO]+ metastable peak induced by protonated 1-indanone fragmentation is the result of fragmentation of the [C6H5CH2CH2CO]+ isomer ion.  相似文献   

9.
Examination of metastable peak abundance ratios for the elimination of HNC vs. DNC from the [M-ketene]+· ion of various deuterium-labeled acetanilides shows that the structure of this ion resembles aniline rather than cyclohexadieneimine. This is suggested to hold also for substituted acetanilides.  相似文献   

10.
Reactivity differences between odd ([M]+) and even electron ions (α-cleavage product) were studied by comparing water elimination mechanisms in 6-undecanol. The compounds specifically labelled with deuterium in positions 6, 5 + 7, 4 + 8 and 3 + 9 were made, and a detailed investigation of tghe metastable ion transitions carried out. A highly specific 1,4 elimination of water without preceding intramolecular hydrogen exchange occurs from [M]+, but equal amounts of 1,3 and 1,4 elimination of water preceded by specific hydrogen exchange between -OH and the hydrocarbon chain occurs from the α-cleavage ion [M – C5H11]+ . To make such distinctions a thorough examination of metastable ions is essential.  相似文献   

11.
The structure and fragmentation of eight [C6H13O] + ions formed by protonation of C6H12O carbonyl compounds in the gas phase have been investigated using isotopic labeling and metastable ion studies to investigate the fragmentation reactions and collisional dissociation studies to probe ion structures. Protonated 3-methyl-2-pentanone and protonated 2-methyl-3-pentanone readily-interconvert by pinacolic-retro-pinacolic rearrangements; the remaining six ions represent stable ion structures, although in many cases fragmentation is preceded by pinacolic-type rearrangements. Unimolecular (metastable ion) fragmentation of the [C6H13O] + species occurs by elimination of H2O, C3H6, C4H8 and C2H4O. The last three elimination reactions appear to occur through the intermediacy of a proton-bound complex of a carbonyl compound and an olefin, with the proton residing with the species of higher proton affinity on decomposition of the complex.  相似文献   

12.
The electron-impact induced fragmentation of 3,5-diphenyl-1,2,4-oxadiazole has been investigated by labelling experiments, defocused metastable ion detections and high resolution mass measurements. The main fragmentation process suggests heterocyclic cleavage at the 1 to 5 and 3 to 4 bonds confirming our previous interpretation. The structure of the major fragment ion [C7H5NO]+· has been interpreted as being represented by the isomeric benzonitrile oxide and phenylisocyanate structures, the latter isomerising irreversibly from the former. The benzonitrile oxide structure is consistent with [C7H5NO]+· formation by cleavage of the 1 to 5 and 3 to 4 bonds.  相似文献   

13.
First field free region metastable fragmentations of (η6-PhCH3)Cr(CO)3 have been examined by means of the linked scan technique. The molecular ion is shown to fragment exclusively by single and multiple CO loss. The ion [C7H8Cr(CO)2]+? also fragments directly to [C7H8Cr]+?.  相似文献   

14.
Collisionally activated dissociation (CAD) mass spectra sometimes appear to be identical in spite of the fact that the precursor ion structures are known to differ. It is shown that determination of the experimental overall cross-section for collisionally activated decomposition yields valuable extra information. After applying it to examples of known structure, [C4H5N], [C5H5N] and [C5H5O]+, it is used to study a more complex problem, that of [C6H6] ions from four isomeric precursors.  相似文献   

15.
The metastable ions [M]2+, [M – H]2+· and [M – H2]2+ from malononitrile fragment by loss of [CH]+, [C]+· and [C]+·, respectively. The reaction of the molecular ion involves the methylene and nitrile carbon atoms in the statistical probability ratio, while that of [M – H]2+· involves exclusively the nitrile carbon and that of [M ? H2]2+ involves an approximately equal contribution, from both sources. It is suggested that the metastable molecular ion fragments through a bipyrimidal intermediate.  相似文献   

16.
The energetics, metastable characteristics and daughter ion structures for the loss of small alkane molecules from ionized 2-propanol, 2-butanol and 3-pentanol have been examined in detail. [2-Propanol] ions lose CH4 to generate the keto and enol forms of [C2H4O] and the same daughter ions are produced by loss of C2H6 from [2-butanol]. Ionized 3-pentanol does not lose CH4 but readily eliminates C2H6 to produce the enol ion [CH3CH?CHOH]. The last reaction was shown to proceed by a simple 1,2 elimination mechanism in the μs time-frame; isotope effects are also discussed.  相似文献   

17.
The mass spectra of norbornene, nortricyclene and deuterium labeled derivatives thereof have been studied. The appearance potentials of the ions [C7H10], [C7H9]+, [C6H7]+ and [C5H6] have been determined for both compounds and heats of formation of the hydrocarbons have been estimated. Detailed fragmentation schemes are proposed for the molecular ions and it is concluded that they dissociate by essentially different mechanisms which do not involve common intermediates. The structures and energy contents of the primary fragment ions are discussed in detail by comparing energetics, labeling experiments and metastable ion abundances.  相似文献   

18.
The unimolecular decomposition of trimethoxyphenylsilane (1) was investigated by mass-analysed ion kinetic energy (MIKE) spectrometry, deuterium-labelling studies and from high resolution data. The characteristic fragmentations of metastable molecular ion of 1 were losses of C6H6 and C7H7· with rearrangements. Almost complete H/D scrambling occurred in the molecular ion prior to these decompositions. The other important fragmentation routes corresponded to expulsions of CH3O· and C6H5·. These fragmentations were followed by consecutive elimination of an H2CO molecule, as commonly observed in the mass spectra of alkoxysilanes. In these fragmentation processes, H/D scrambling increased as the internal energy of the molecular ion was lowered. The fragmentations of 1 were compared with those of its carbon analogue, α,α,α-trimethoxytoluene.  相似文献   

19.
[C13H9S]+, [C14H11]+, [C13H11]+ and [C8H7S]+ ions with unknown structures were generated from two [C14H12S]precursor ions by fragmentation reactions that must be preceded by extensive rearrangements. Ions with the same compositions, each with several initial structures, were prepared by simple bond-breaking reactions. Metastable characteristics were compared for each of the four types of ions. It was found than in all cases fast isomerization reactions occur prior to fragmentation, so that no information about the unknown ion structures could be obtained by comparison of the observed fragmentations of metastable ions.  相似文献   

20.
The mass spectra of a series of β-ketosilanes, p-Y? C6H4Me2SiCH2C(O)Me and their isomeric silyl enol ethers, p-Y? C6H4Me2SiOC(CH3)?CH2, where Y = H, Me, MeO, Cl, F and CF3, have been recorded. The fragmentation patterns for the β-ketosilanes are very similar to those of their silyl enol ether counterparts. The seven major primary fragment ions are [M? Me·]+, [M? C6H4Y·]+, [M? Me2SiO]+˙, [M? C3H4]+˙, [M? HC?CCF3]+˙, [Me2SiOH]+˙ and [C3H6O]+˙ Apparently, upon electron bombardment the β-ketosilanes must undergo rearrangement to an ion structure very similar to that of the ionized silyl enol ethers followed by unimolecular ion decompositions. Substitutions on the benzene ring show a significant effect on the formation of the ions [M? Me2SiO]+˙ and [Me2SiOH]+˙, electron donating groups favoring the former and electron withdrawing groups favoring the latter. The mass spectral fragmentation pathways were identified by observing metastable peaks, metastable ion mass spectra and ion kinetic energy spectra.  相似文献   

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