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1.
Appearance energies for [C7H7]+ and [C6H5]+ fragment ions obtained from methylphenol isomers were measured at the threshold using the electron impact technique. Different processes for the formation of the ions are suggested and discussed. Metastable peaks were detected and the kinetic energies released were determined. The results indicate that [C7H7]+ ions are formed from metbylpbenois with both benzyl and tropylium structures, whereas [C6H5]+ ions are formed with the phenyl structure at the detected thresholds. Kinetic energies released on fragmentation of reactive [ C7H7]+ and [C6H5]+ ions were used as a probe for the structure of the ions at 70 eV. 相似文献
2.
The ions [CF3CO2]+ and [CH3CO2]+ give peaks of small abundance in conventional positive ion spectra. These ions can be produced by collision-induced charge stripping of the corresponding stable negative ions. Six and ten fragment ions respectively are observed in the spectra of [CF3CO2]+ and [CH3CO2]+. 相似文献
3.
An energetic study of the production of [C7H8N]+ and [C6H7]+ fragment ions from o-toluidine and N-methylaniline is reported. The mechanisms for the formation of the ions are suggested. Metastable peaks associated with the formation and fragmentation of reactive [C7H8N]+ and [C6H7]+ ions were detected and kinetic energy released were determined. The results indicate that the [C7H8N]+ ion is formed at threshold from o-toluidine with an aminotropylium structure whereas for N-methylaniline the ion is formed with anN-phenylmethaniminium structure. [C6H7]+ ions are believed to be formed at threshold from the two precursors with a protonated benzene structure. 相似文献
4.
D. Amos R. G. Gillis J. L. Occolowitz J. F. Pisani 《Journal of mass spectrometry : JMS》1969,2(2):209-212
The mass spectra of deuterated species shows that both the isomeric ions [CH2?SH]+ and [CH3? S]+ are formed in the ratio 2:1 from CH3SH; the ions [CH3CH?SH]+ and [CH3CH2S]+ in the ratio 0·8:1 from CH3CH2SH; and [CH2?OH]+ and [CH3? O]+ in the ratio 6·7:1 from methanol. The heats of formation of [CH3S]+ and [C2H5S]+ are of the order of 222 and 203 Kcal.mole?1 respectively. The isomeric ions cannot be distinguished on thermodynamic grounds. 相似文献
5.
Marcel Rietjens Drewes Oudman Wilke D. Weringa 《Journal of mass spectrometry : JMS》1990,25(5):285-288
[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
6.
G. Bouchoux Y. Hoppilliard R. Flammang A. Maquestiau P. Meyrant 《Journal of mass spectrometry : JMS》1983,18(8):340-344
It is demonstrated by means of collisionally activated decomposition (CAD) that [C3H5O]+ originating from metastable [C4H8O]+˙ ions are either acylium [C2H5CO]+ (a) or hydroxycarbenium [CH2CHCHOH]+ (b). Butanone gives exclusively a but 2-methyl-2-propen-1-ol, 2-buten-1-ol, 3-buten-1-ol, butanal and 2-methylpropanal lead to ion b. Both structures a and b are produced from 3-buten-2-ol. These results are discussed in conjunction with experimental and calculated (MINDO/3) thermodynamic data. 相似文献
7.
The structure and decomposition of the [C7H7]+ ions produced by electron-impact from o-, m- and p-chlorotoluene, o-, m- and p-bromotoluence, and p-iodotoluence, have been investigated. By determining the relative abundance of normal and metastable ions, these [C7H7]+ ions at electron energy of 20 eV are shown to be so-called ‘tropylium ions’. The amount of the internal energy of the [C7H7]+ ion estimated by the relative ion abundance ratios, ? [C5H5]+/[C7H7]+ and m*/[C7H7]+ for the decomposition \documentclass{article}\pagestyle{empty}\begin{document}$ [{\rm C}_{\rm 7} {\rm H}_{\rm 7}]^ + \mathop \to \limits^{m^* } [{\rm C}_{\rm 5} {\rm H}_{\rm 5}]^ + + {\rm C}_{\rm 2} {\rm H}_{\rm 2} $\end{document}, is in the order iodotoluene > bromotoluene > chlorotoluene. The heats of formation of the activated complexes for the reaction \documentclass{article}\pagestyle{empty}\begin{document}$ [{\rm C}_{\rm 7} {\rm H}_{\rm 7}]^ + \mathop \to \limits^{m^* } [{\rm C}_{\rm 5} {\rm H}_{\rm 5}]^ + + {\rm C}_{\rm 2} {\rm H}_{\rm 2} $\end{document} were estimated. The values suggest that the decomposing [C7H7]+ ions from various halogenotoluenes are identical in structure. 相似文献
8.
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
9.
Susumu Tajima Tadashige Azami Toshikazu Tsuchiya 《Journal of mass spectrometry : JMS》1977,12(1):24-27
The decomposition of the [C6H5CO]+ ions produced from eight alkyl benzoates by electron impact has been studied. By calculating the heat of formation of [C6H5CO]+ ions from the appearance potential value, it is shown that the ions from C6H5COOR when R?H, CH3, C2H5 have some excess energy, and those where R = n-C3H7, iso-C3H7, n-C4H9, iso-C4H9, iso-C5H11 are produced with more excess energy. It is also shown that by taking this excess energy into account, there is a linear relationship between the heat of formation of the activated complex produced in the reaction [C6H5CO]+→[C6H5]+ + CO and the vibrational degree of freedom of the neutral fragment ? OR. 相似文献
10.
Collisional activation spectra of [C8H8]+·, [C8H8]2+, [C6H6]+· and [C6H5]+ ions from fifteen different sources are reported. Decomposing [C8H8]+· ions of ten of these precursors isomerise to a mixture of mainly the cyclooctatetraene and, to a smaller extent, the styrene structure. Three additional structures are observed with [C8H8]+· ions from the remaining precursors. [C8H8]2+., [C8H8]+·, [C6H6]+· and [C6H5]+· ions mostly decompose from common structures although some exceptions are reported. 相似文献
11.
Johan K. Terlouw Peter C. Burgers Henk Hommes 《Journal of mass spectrometry : JMS》1979,14(10):574-576
Characterization of [C4H5O]+ ions in the gas phase using their metastable ion and collisional activation spectra shows that the three isomeric ions HC?C? \documentclass{article}\pagestyle{empty}\begin{document}$ \mathop {\rm C}\limits^{\rm + } $\end{document}H? OCH3, CH3O? \documentclass{article}\pagestyle{empty}\begin{document}$ \mathop {\rm C}\limits^{\rm + } $\end{document}?C?CH2 and ? OCH3 related to the two stable [C3H3]+ cations [HC?C? CH2]+ and are stable for ≥ 10?5s. In contrast to the formation of cyclopropenium ions, it is found that the methoxy cyclopropenium ion is not generated from acyclic precursor molecules. The small but significant intensity differences found in the collisional activation spectra of [C3H3]+ ions generated from HC?C? CH2I and HC?C? CH2Cl possibly indicate the presence of [C3H3]+ ions of different structures. 相似文献
12.
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
13.
R. G. Cooks J. H. Beynon M. Bertrand M. K. Hoffman 《Journal of mass spectrometry : JMS》1973,7(11):1303-1312
The use of kinetic energy release measurements in the structural characterization of ions formed in the mass spectrometer and in the determination of fragmentation mechanisms is demonstrated. In combination with information on the mode of energy partitioning in some of these reactions this allows the following conclusions: (i) The metastable [C7H8]8˙ ions formed from toluene, cyclohepatatriene, n-butylbenzene, the three methyl anisoles, methyl tropyl ether and benzyl methyl ether all undergo loss of H˙ from a common structure. (ii) The metastable [C7H7]+ ions generated from the same sources and from benzyl bromide, benzyl alcohol, p-xylene and ethylbenzene appear to undergo loss of acetylene from both the benzylic and the tropylium structures. (iii) The metastable [C7H7OCH3]+˙ ether molecular ions undergo loss of CH3˙ by two types of mechanism, simple cleavage to give the aryloxy cation (not observed for benzyl methyl ether) and a rearrangement process which appears to lead to protonated tropone as the product. (iv) Loss of formaldehyde from the metastable [C7H7OCH3]+˙ molecular ions involves hydrogen transfer via competitive 4- and 5-membered cyclic transition states in the case of the anisoles and in the case of methyl tropyl ether, while for benzyl methyl ether, hydrogen transfer in the nonisomerized molecular ion occurs via a 4-membered cyclic transition state to yield the cycloheptatriene molecular ion. 相似文献
14.
Johan K. Terlouw Peter C. Burgers Henk Hommes 《Journal of mass spectrometry : JMS》1979,14(7):387-398
The abundant [C4H5O]+ (m/z 69) ions found in the 70 eV mass spectra of a series of acetylenic, allenylic and unsaturated cyclic ethers are shown to have the following structures: HC?C? \documentclass{article}\pagestyle{empty}\begin{document}$ \mathop {\rm C}\limits^{\rm + } $\end{document}H? OCH3 (e), H2C?C?—OCH3 (f), (g) and H? C?C? CH2—O\documentclass{article}\pagestyle{empty}\begin{document}$ \mathop {\rm C}\limits^{\rm + } $\end{document}H2 (h). Of these, the cyclic ion g is the most stable: its ion enthalpy (≥ 165 kcal mol?1) is close to that found for the acyclic C3H5\documentclass{article}\pagestyle{empty}\begin{document}$ \mathop {\rm C}\limits^{\rm + } $\end{document}? O isomers identified in a previous study. Evidence that these four isomeric [C4H5O]+ ions are stable species with lifetimes ≥ 10?5 s is obtained from their collisional activation spectra, the shape of the metastable peaks and the associated kinetic energy release values for the common loss of CO, thermochemical information and analysis of deuterium and carbon-13 labelled precursor molecules. It is further shown that loss of X? from ethers of the type X? C?C? CH2OCH3 involves isomerization into energy rich allenyl type ions [(X)HC?C?CHOCH3]+˙ . These ions undergo loss of X? by simple bond cleavage, yielding, e type product ions, when the C? X bond strength is relatively low (X?I, Br). When X?Cl and especially CH3 or H, X? is only lost after rearrangement yielding the cyclic product ion g. The mechanism for this cyclization reaction is related to that proposed in a previous study for the ester→ acid isomerization in the molecular ions of the esters of α, β-unsaturated carboxylic acids. 相似文献
15.
The principal fragmentation reactions of metastable [C3H7S]+ ions are loss of H2S and C2H4. These reactions and the preceding isomerizations of [C3H7S]+ ions with six different initial structures were studied by means of labelling with 13C or D. From the results it is concluded that the loss of H2S and C2H4 both occur at least mainly from ions with the structure [CH3CH2CH? SH]+ or from ions with the same carbon sulfur skeleton, with the exception of the ions with the initial structure [CH3CH2S? CH2]+, which partly lose C2H4 without a preceding isomerization. For all ions, more than one reaction route leads to [CH3CH2CH?SH]+. It is concluded that the loss of H2S is at least mainly a 1,3-elimination from the [CH3CH2CH?SH]+ ions. Both decomposition reactions are preceded by extensive but incomplete hydrogen exchange. 相似文献
16.
From deuterium labelling experiments it was concluded that metastable molecular ions of ethyl methyl sulfide lose a methyl radical with the formation of both [CH3S?CH2]+ amd [CH3CH?SH]+˙ The fragmentation reactions of metastable ions generated with these structure are losses of C2H2, H2S and CH4. These reactoins and the preceding isomerizations have also been studied by means of deuterium labelling. From the results it is concluded that the three fragmentation reactions most probably occur from ions with a C? C? S skeleton. Appearance energy measurements for ions generated with the two structures above and all give rise to the same ΔHf value for these three isomeric forms. Ab initio molecular orbitals calculations confirm that these three ions fortuitously have very similar heats of formation. A potential energy diagram rationalizing the isomerizations and the principal fragmentation reaction is presented. 相似文献
17.
[C2H5S]+ ions (m/e 61) with different initial structures were generated in the mass spectrometer from twelve precursor ions. Abundance ratios of competing metastable ion decompositions were used to determine whether these ions decompose through the same or different reaction channels. It was concluded that all [C2H5S]+ ions isomerize to a common structure or mixture of structures prior to decomposition in the first field free region. From 13C labelling experiments it was concluded that [C2H5S]+ ions generated from the molecular ions of 2-propanethiol-2-[13C], partially rearrange to a symmetrical structure before decomposition to [CHS]+ and CH4, whereas in [C2H5S]+ ions generated from the the molecular ions of 1,2-bis-(thiomethoxy-[13C]) ethane, the two carbon atoms become fully equivalent before CH4 loss occurs. 相似文献
18.
G. Bouchoux Y. Hoppilliard P. Jaudon R. Houriet 《Journal of mass spectrometry : JMS》1984,19(8):394-397
The proton transfer equilibrium reactions involving 3-penten-2-one, 3-methyl-3-buten-2-one, crotonic acid and methacrylic acid were carried out in an ion cyclotron resonance (ICR) spectrometer. The semiempirical method MNDO, used to estimate the heats of formation for 14 protonated [C5H9O]+ and [C4H7O2]+ ions and the energetic aspect of the fragmentations of metastable [C6H12O]+. and [C6H12O2]+. ions, leads to the conclusion that the ions corresponding to protonation at the carbonyl oxygen are the most stable. Thus the experimentally determined heats of formation of protonated olefinic carbonyl compounds can be attributed to the following structures: [CH3COHCHCHCH3]+ (δHf = 490 KJ mol?1), [CH3COHC(CH3)CH2]+ (δHf = 502 KJ mol?1), [HOCOHCHCHCH3]+ (δHf = 330 KJ mol?1) and [HOCOHC(CH3)CH2]+ (δHf = 336 KJ mol?1). 相似文献
19.
From a comparison of the metastable ion bundance ratios for loss of C2H4 and H2S from [C3H7S]+ ions in a series of alkyl thio ethers and thiols it was concluded that in most compunds these ion s isomerize to a common structure prior to decomposition in the first field free region. The mechanism for C2H4 loss from the [C3H7S]+ ion gen erated from CH3SCH2CH3 was investigated in detail using 13C and 2H labelling. A rearrangement with formation of a cyclic intermediate prior to the decompistion reaction is proposed. The fragmentation is preceded by extensive hydrogen scrabling. The carbon atoms of the expelled C2H4 molecule are those of the CH2?CH3 moiety. 相似文献
20.
Chhabil Dass 《Journal of mass spectrometry : JMS》1994,29(9):475-482
The chemistry of glycerol subjected to a high-energy particle beam was explored by studying the mass spectral fragmentation characteristics of gas-phase protonated glycerol and its oligomers by using tandem mass spectrometry. Both unimolecular metastable and collision-induced dissociation reactions were studied. Collision activation of protonated glycerol results in elimiation of H2O and CH3OH molecules. The resulting ions undergo further fragmentations. The origin of several fragment ions was established by obtaining their product and precursor ion spectra. Corresponding data for the deuterated analogs support those results. The structures of the fragment ions of compositions [C3H5O]+, [C2H5O]+, [C2H4O]+. and [C2H3O]+ derived from protonated glycerol were also identified. Proton-bound glycerol oligomers fragment principally via loss of neutral glycerol molecules. Dissociation of mixed clusters of glycerol and deuterated glycerol displays normal secondary isotope effects. 相似文献