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1.
Johan K. Terlouw Wigger Heerma John L. Holmes Peter C. Burgers 《Journal of mass spectrometry : JMS》1980,15(11):582-586
The [C4H6O]+˙ ion of structure [CH2?CHCH?CHOH]+˙ (a) is generated by loss of C4H8 from ionized 6,6-dimethyl-2-cyclohexen-1-ol. The heat of formation ΔHf of [CH2?CHCH?CHOH]+˙ was estimated to be 736 kJ mol?1. The isomeric ion [CH2?C(OH)CH?CH2]+˙ (b) was shown to have ΔHf, ? 761 kJ mol?1, 54 kJ mol?1 less than that of its keto analogue [CH3COCH?CH2]+˙. Ion [CH2?C(OH)CH?CH2]+˙ may be generated by loss of C2H4 from ionized hex-1-en-3-one or by loss of C4H8 from ionized 4,4-dimethyl-2-cyclohexen-1-ol. The [C4H6O]+˙ ion generated by loss of C2H4 from ionized 2-cyclohexen-1-ol was shown to consist of a mixture of the above enol ions by comparing the metastable ion and collisional activation mass spectra of [CH2?CHCH?CHOH]+˙ and [CH2?C(OH)CH?CH2]+˙ ions with that of the above daughter ion. It is further concluded that prior to their major fragmentations by loss of CH3˙ and CO, [CH2?CHCH?CHOH]+˙ and [CH2?C(OH)CH?CH2]+˙ do not rearrange to their keto counterparts. The metastable ion and collisional activation characteristics of the isomeric allenic [C4H6O]+˙ ion [CH2?C?CHCH2OH]+˙ are also reported. 相似文献
2.
John L. Holmes Peter C. Burgers Yousuf A. Mollah 《Journal of mass spectrometry : JMS》1982,17(3):127-130
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
3.
K. Clausen S. Scheibye S.-O. Lawesson J. H. Bowie T. Blumenthal 《Journal of mass spectrometry : JMS》1980,15(12):640-642
The decomposing molecular cations derived from (substituted) 2-nitrothiobenzamides fragment by complex rearrangement reactions. When the alkyl substituents (R) attached to N are methyl, the major fragmentations are [M]+˙ → [M? SO]+˙ and [M? SO]+˙ → [(M? SO)+˙–R˙]+. This remains a basic pathway when R ? Et, but other rearrangements are also observed. For example, when R=Et, additional competitive processes are [M]+˙ → [M? HO˙]+ and [M]+˙ → [M? C2H4O]+˙. 相似文献
4.
The gas phase heats of formation of several organosulfur cations were determined from thiirane, thietane and tetrahydrothiophene precursor molecules by photoionization mass spectrometry. Heats of formation at 0 K and 298 K are reported for the following ions: [H2CS]+˙, [H3CS]+, [C2H3S]+, [C2H4S]+˙, [C3H5S]+, [C3H6S]+˙, [C4H7S]+ and [C4H8S]+˙. The [C4H7S]+ (m/z 87), [C2H4S]+˙ (m/z 60), [C2H3S]+ (m/z 59), [C4H7]+ (m/z 55), [C4H6]+˙ (m/z 54) and [CH2S]+˙ (m/z 46) ions are produced from metastable tetrahydrothiophene ions at photon energies between 10.2 and 10.7 eV. Decay rates of internal energy selected parent ions to the m/z 60, 59, 55 and 54 fragments were measured by threshold photoelectron-photoion coincidence, the results of which are compared to statistical theory (RRKM/QET) calculations. The [C2H4S]+˙ ion from tetrahydrothiophene is found to have the thioacetaldehyde structure. From the measured [C2H4S]+˙ onset a ΔH = 50±8 kJ mol?1 was calculated for the thioacetaldehyde molecule. 相似文献
5.
J. W. Dallinga N. M. M. Nibbering G. J. Louter 《Journal of mass spectrometry : JMS》1981,16(4):183-187
The structure and formation of [C8H8O]+. ions generated from phenylcyclopropylcarbinol and 1-phenyl-1-hydroxymethylcyclopropane upon electron impact, have been studied using kinetic energy release measurements, by determination of ionization and appearance energies and by collisional activation. It is shown that the non-decomposing [C8H8O]+˙ ions have exclusively the structure of the enol ion of phenylacetaldehyde, although it is less stable than the enol ion of acetophenone by about 45 kJ mol?1. This has been interpreted as an indication that the [C8H8O]+˙ ions from phenylcyclopropylcarbinol are formed by an attack of either the phenyl ring or the hydroxyl group upon the C-1? C-2 (or C-1? C-3) bond of the cyclopropane ring under a simultaneous expulsion of ethene and migration of the attacking group to the C-1 position. The [C8H8O]+˙ ion from 1-phenyl-1-(hydroxymethyl)cyclopropane is formed by opening of the cyclopropane ring via a benzylic cleavage. A kinetically controlled hydrogen shift in the resulting ring opened ion prior to or during ethene loss then leads to the formation of [C8H8O]+˙ ions which have the structure of the enol ion of phenylacetaldehyde. 相似文献
6.
Nitric oxide chemical ionization mass spectra of substituted benzenes obtained with the Townsend discharge technique were studied. There were four kinds of base peaks in the mass spectra, i.e. [M + NO]+˙, M+˙, [M ? H]+ and [M ? OR]+ (R = H, CH3). The formation of the specific ion [M + NO]+˙ was highly dependent on the kind of substituent, and it was produced more abundantly in the case of substitutions involving electron-accepting groups. The measure of [M + NO]+˙ production was evaluated from the value of the ratio [M + NO]+˙/M+˙. In mono-substitutions, it was clarified that the ratios of [M + NO]+˙/M +˙ were correlated with the Hammett substituent constant s?p or the electrophilic substituent constant s?p+. Monosubstitutions (C6H5R) and toluene substitutions (CH3C6H4R) could be classified into six groups in terms of base peak species, [M + NO]+˙/M+˙ ratios and substituents. In disubstitutions, the mass spectral patterns were governed by the combination of substituents. Mass spectral distinctions among ortho, meta and para isomers could be made in many cases. 相似文献
7.
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
8.
Lawrence L. Griffin David J. McAdoo Santiago Olivella 《Journal of computational chemistry》1993,14(12):1561-1574
AM1 semiempirical molecular orbital calculations are reported for 20 ion-neutral complexes, including hydrogen-bonded complexes, presumably involved in the gas-phase unimolecular decomposition of simple organic radical cations. The systems investigated are [C2H4O2]˙+, [C2H5NO]˙+, [C2H6O]˙+, [C2H6O2]˙+, [C3H6O]˙+, [C3H6O2]˙+, [C3H8O]˙+, and [C3H8O2]˙+. The AM1 results are compared with ab initio molecular orbital calculations at different levels of theory up to MP3/6-31G(d, p)//SCF/6-31G(d) + ZPVE and the available experimental data. AM1 fails to predict some local minima and the equilibrium geometries calculated for several complexes are found to be qualitatively different from those predicted by the ab initio calculations. However, reasonable agreement is generally found for the stabilization energies of the complexes toward dissociation into their loosely bound components. © John Wiley & Sons, Inc. 相似文献
9.
Water elimination from ionized n-butanol reflects near randomization of all hydrogens in ions decomposing after ~10?5s. This probably takes place in ion-neutral complexes by formation of a cyclobutane ion–H2O complex and/or rearrangement within [C4H8]+˙ in open-chain [C4H8+˙? H2O] complexes, in either case accompanied by hydrogen exchange between water and open-chain hydrocarbon moieties. Extensive hydrogen rearrangements in which restraints on conventional transition-state ring size have little apparent influence may generally be ion–neutral complex-mediated processes. 相似文献
10.
Seymour Meyerson Catherine Fenselau J. L. Young W. R. Landis Edward Selke L. C. Leitch 《Journal of mass spectrometry : JMS》1970,3(6):689-707
The mass spectra of hexanal, heptanal and nonanal variously labeled with deuterium confirm γ-hydrogen migration and β cleavage as the mechanism leading to [C2H4O]+˙ and [M ? C2H4O]+˙, although the data on the latter are complicated by contributions from other, related paths. In addition, they show that three other major primary decomposition products, [M ? C2H4]+˙, [M ? H2O]+˙ and [C3H5O]+, all arise in large part by processes involving γ-hydrogen migration to the oxygen atom. The ethylene lost to yield the first of these products consists of the α and β methylene groups. The loss of ethylene most likely occurs by way of a cyclobutanol intermediate, which, via alternative reaction paths, may well contribute to the yields of the other two products as well. These findings further extend the range of parallelism between photochemical and electron-impact-induced reactions. 相似文献
11.
Cornelis E. C. A. Hop Hongwen Chen P. J. A. Ruttink John L. Holmes 《Journal of mass spectrometry : JMS》1991,26(8):679-687
The isomeric ions [H2NC(H)O]+˙, [H2NCOH]+˙, [H3CNO]+˙ and [H2CNOH]+˙ were examined in the gas phase by mass spectrometry. Ab initio molecular orbital theory was used to calculate the relative stabilities of [H2NC(H)O]+˙, [H2NCOH]+˙, [H3NCO]+˙ and their neutral counterparts. Theory predicted [H2NC(H)O]+˙ to be the most stable ion. [H2NCOH]+˙ ions were generated via a 1,4-hydrogen transfer in [H2NC(O)OCH3]+˙, [H2NC(O)C(O)OH]+˙ and [H2NC(O)CH2CH3]+˙. Its metastable dissociation takes place via [H3NCO]+˙ with the isomerization as the rate-determining step. [H2CNOH]+˙ undergoes a rate-determining isomerization into [H3CNO]+˙ prior to metastable fragmentation. Neutralization-reionization mass spectrometry was used to identify the neutral counterparts of these [H3,C,N,O]+˙ ions as stable species in the gas phase. The ion [H3NCO]+˙ was not independently generated in these experiments; its neutral counterpart was predicted by theory to be only weakly bound. 相似文献
12.
Robert S.-C. Tsai Gerald L. Larson Alfonso Oliva 《Journal of mass spectrometry : JMS》1979,14(7):364-368
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
13.
Kalevi Pihlaja Pirjo Vainiotalo Gbor Bernth Gyrgy Gnds Lajos Gera 《Journal of mass spectrometry : JMS》1986,21(2):55-57
Electron impact induced fragmentation of the title compounds obeys a route where the lactam moiety, OCNH, is cleaved first, with the accompanying formation of a cycloalkene ion. This can be verified by low-resolution, high-resolution, B/E and B2/E spectra as well as by collisional activation spectra of, for example, the ions m/z 82 and 67 from 7-azabicyclo[4.2.0]octan-8-one and from cyclohexene. The only, and fairly weak, fragment ions including O and N are [C3H3O]+, [CkH2k-2N]+ (k = 5–8) and [C3H6N]+. The ammonia chemical ionization spectra are also characteristic for all four lactams and show the same dominant ions in all cases, namely [M + 1]+, [M + 1 + NH3]+˙ and [2 M + 1]+˙. 相似文献
14.
The low-energy, low-temperature mass spectra of thirteen alkanals are reported and their predominant modes of fragmentation discussed in terms of energetics. Characteristic of this class of compounds is the very high proportion of odd-electron ions in the mass spectra, namely [M ? CMH2m]+˙, [M ? H2O]+˙ and [M ? H2O ? CmH2m]+˙. 相似文献
15.
[C4H5N]+˙ ions have been generated from eleven neutral species. From a study of their metastable transitions and the translational energy released in the fragmentation in which C2H2 is lost, it is concluded that [C4H5N]+˙ ions with sufficient energy to decompose do so from a common structure or mixture of structures when they are generated from crotonitrile, allyl cyanide, cyclopropyl cyanide, methacrylontrile, pyrrole, 2-, 3- and 4-hydroxypyridines and 2-aminopyridine. The [C4H5N]+˙ ions formed from allyl isocyanide decompose from a different structure and those given by cyclopropyl isocyanide appear to decompose from a mixture of the two structures. Non-decomposing [C4H5N]+˙ ions were investigated by means of their collision induced decomposition spectra using a B/E linked scan. Six different structures or mixtures of structures are suggested to explain these observations. 相似文献
16.
Ion cyclotron resonance studies using deuterium labelled substrates have revealed a more complex mechanism than previously proposed for the structure-specific ion/molecule reaction of the [C2H4O]+˙ and [C3H6O]+˙ enol ions with neutral cyclobutanol. This requires the intermediacy of a species in which all of the methylene groups present in both the reactant ion and neutral can become equivalent. 相似文献
17.
The decomposition reactions of [C2H5O]+ ions produced by dissociative electron-impact ionization of 2-propanol have been studied, using 13C and deuterium labeling coupled with metastable intensity studies. In addition, the fragmentation reactions following protonation of appropriately labeled acetaldehydes and ethylene oxides with [H3]+ or [D3]+ have been investigated. In both studies particular attention has been paid to the reactions leading to [CHO]+, [C2H3]+ and [H3O]+. In both the electron-impact-induced reactions and the chemical ionization systems the fragmentation of [C2H5O]+ to both [H3O]+ and [C2H3]+ proceeds by a single mechanism. For each case the reaction involves a mechanism in which the hydrogen originally bonded to oxygen is retained in the oxygen containing fragment while the four hydrogens originally bonded to carbon become indistinguishable. The fragmentation of [C2H5O]+ to produce [CHO]+ proceeds by a number of mechanisms. The lowest energy route involves complete retention of the α carbon and hydrogen while a higher energy route proceeds by a mechanism in which the carbons and the attached hydrogens become indistinguishable. A third distinct mechanism, observed in the electron-impact spectra only, proceeds with retention of the hydroxylic hydrogen in the product ion. Detailed fragmentation mechanisms are proposed to explain the results. It is suggested that the [C2H5O]+ ions formed by protonation of acetaldehyde or ionization of 2-propanol are produced initially with the structure [CH3CH?\documentclass{article}\pagestyle{empty}\begin{document}$ \mathop {\rm O}\limits^ + $\end{document}H] (a), but isomerize to [CH2?CH? \documentclass{article}\pagestyle{empty}\begin{document}$ \mathop {\rm O}\limits^ + $\end{document}H2] (e) prior to decomposition to [C2H3]+ or [H3O]+. The results indicate that the isomerization a → e does not proceed directly, possibly because it is symmetry forbidden, but by two consecutive [1,2] hydrogen shifts. A more general study of the electron-impact mass spectrum of 2-propanol has been made and the fragmentation reactions proceeding from the molecular ion have been identified. 相似文献
18.
Unstable 2-hydroxpropene was prepared by retro-Diels-Alder decomposition of 5-exo-methyl-5-norbornenol at 800°C/2 × 10?6 Torr. The ionization energy of 2-hydroxypropene was measured as 8.67±0.05 eV. Formation of [C2H3O]+ and [CH3]+ ions originating from different parts of the parent ion was examined by means of 13C and deuterium labelling. Threshold-energy [H2C?C(OH)? CH3]+˙ ions decompose to CH3CO++CH3˙ with appearance energy AE(CH3CO+) = 11.03 ± 0.03 eV. Higher energy ions also form CH2?C?OH+ + CH3 with appearance energy AE(CH2?C?OH+) = 12.2–12.3 eV. The fragmentation competes with hydrogen migration between C(1) and C(3) in the parent ion. [C2H3O]+ ions containing the original methyl group and [CH3]+ ions incorporating the former methylene and the hydroxyl hydrogen atom are formed preferentially, compared with their corresponding counterparts. This behaviour is due to rate-determining isomerization [H2C?C(OH)? CH3]+˙ →[CH3COCH3]+˙, followed by asymmetrical fragmentation of the latter ions. Effects of internal energy and isotope substitution are discussed. 相似文献
19.
The mass spectra of diethyl phenyl phosphates show substituent effects with electron-donating groups favouring the molecular ion M+˙, and the [M? C2H4]+˙, [M – 2C2H4]+˙ and [XPhOH]+˙ ions. The [PO3C2H6]+ (m/z 109) and [PO3H2]+ (m/z 81) ions are favoured by electron-withdrawing groups. Results suggest that the formation of the [XPhC2H3]+˙ ion involves rearrangement of C2H3 to the position ortho to the phosphate group. Ortho effects are also observed. 相似文献
20.
Fragmentation pathways of isoxazole giving ions [C3H2ON]+, [C2H3N]+˙ and [C2H2N]+ are elucidated by means of metastable ion studies and thermodynamic properties. Rearrangement reactions are demonstrated to occur with H and HCO loss. Elimination of carbon monoxide leads to [C2H3N]+˙ ions whose reacting configuration is the same as for acetonitrile. All these results can be rationalized in terms of a prior isomerization of isoxazole involving ring opening and 1,2 H migration. 相似文献