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1.
Antonio Selva Umberto Vettori Enrico Gaetani 《Journal of mass spectrometry : JMS》1974,9(12):1161-1165
1,2-Benzisothiazole and benzothiazole ion kinetic energy spectra, and metastable ion relative abundances of the same primary and secondary decomposition processes are compared. The results are interpretable as postulating slow (metastable) process(es) involving common structures and fast process(es)which are structurally dependent. Analogous indications are given by the interring H/D scrambling data, preceding the loss of DCN (or HCN) from 1,2-benzisothiazole-3-d1 and benzothiazole-2-d1 molecular ions, measured in either metastable or normal daughter ions at various electron beam energies. 相似文献
2.
S. Safe 《Journal of mass spectrometry : JMS》1973,7(12):1329-1336
The mass spectra of several substituted diphenylacetylenes are reported and the [metastable ion]/[daughter ion] ratios for the isomeric chloro- and bromodiphenylacetylenes suggested substituent scrambling in their respective molecular ions. The metastable ion data also indicated equilibration of the chloro substituents in a series of isomeric dichlorodiphenylacetylenes. In addition, the fragmentation patterns for the amino- and nitrodiphenylacetylenes differed somewhat from most other aromatic amino and nitro compounds. The aminodiphenylacetylenes fragment with expulsion of H2CN from the molecular ion and the expulsion of HCN from the [M – 1]+ ion was only a relatively minor reaction. 4-Nitrodiphenylacetylene loses NO from the molecular ion and OH from the [M – NO]+˙, whereas the more familiar loss of OH from the molecular ion was not observed. The mass spectra of several deuterated substituted diphenylacetylenes clearly showed extensive (but not complete) H/D equilibration in the molecular ion or some subsequent decomposition ion. Comparative studies between 4-chloro and 4-bromo substituted biphenyl, diphenylacetylene and diphenyldiacetylene indicated similar degrees of H/D randomization, and the results showed that the ? C?C? group did not inhibit the proton equilibration between the two phenyl groups. 相似文献
3.
Anders Hallberg Ibrahim Al-Showaier Arnold R. Martin 《Journal of heterocyclic chemistry》1984,21(3):841-844
Electron impact induced fragmentation patterns of simple phenothiazines have been reinvestigated using metastable ion studies, exact mass measurements and deuterated derivatives. Secondary fragmentation processes involving ions m/e 198, 171, 167, 166, 154, 140 and 139 have been clarified. Mechanisms for the release of sulfur (SH· and CSH·) nitrogen (HCN and H2CN·) containing fragments from phenothiazine molecular ion are proposed based on the deuterium content of the daughter ions obtained from 1,9-dideutenophenothiazine. A revised mechanism for the expulsion of ketene from 10-acetylphenothiazine is suggested based on the fragmentation pattern of the 1,9-dideuterioderivative. The composition of m/e 140 was determined by high resolution measurement to be C10H6N and not C11H7 as previously reported. 相似文献
4.
The negative-ion mass spectra of 2-aryl-1,3-dithianes contain pronounced molecular anions together with fragment ions which are produced by both simple and complex cleavage reactions. These spectra contain further examples of specific hydrogen scrambling processes in negative ions. Nitroaryldithianes give intense negative-ion spectra, and that of the o-nitro derivative exhibits an unusual proximity effect. The fragmentation patterns have been examined using both 2H and 13C labelling and the metastable defocusing technique. 相似文献
5.
P. Goldberg J. A. Hopkinson A. Mathias A. E. Williams 《Journal of mass spectrometry : JMS》1970,3(8):1009-1021
The n-alkanes, propane to heptane, have been studied in a modified MS-9 mass spectrometer under conditions that enabled the daughter ions, resulting from metastable fragmentation processes occurring in the first field free region, to be observed with high sensitivity. The precursor ions in these fragmentations have been identified unambiguously and a general fragmentation scheme for the n-alkanes is proposed. The mass spectrometer incorporated a variable width monitor slit and narrow settings of this slit improved the energy resolution so that fine structure could be observed in some of the ‘metastable peaks’. The implications of this fine structure are discussed. 相似文献
6.
The electron-impact-induced fragmentation of a 13C labelled exo-2-norbornyl chloride has been studied. When the norbornyl cation, [C7H11]+, [M – Cl], dissociates by elimination of C2H4, carbon atoms are randomly lost showing that extensive skeletal rearrangement (in addition to the complete hydrogen atom scrambling reported earlier) has taken place in the norbornyl cation prior to dissociation. The metastable ion peak associated with the above fragmentation consists of superimposed gaussian and flat-top components; it is proposed that these correspond to the formation of isomeric [C5H7]+ daughter ions whose heats of formation differ by ~0.4 eV. 相似文献
7.
Low-and high-resolution mass spectra and spectra of metastable ions were studied using direct analysis of daughter ions (DADI)
and metastable defocusing (MD) of lagochiline-type diterpenoids. Patterns in their fragmentation were found.
__________
Translated from Khimiya Prirodnykh Soedinenii, No. 1, pp. 56–60, January–February, 2007. 相似文献
8.
The metastable transitions in the mass spectra of 21 lycoctonine bases have been studied by the method of metastable defocusing (MD). It has been established that as a criterion of the monotypicity of single-stage fragmentation reactions it is possible to use a linear dependence of the relative intensities of the metastable peaks (MPs) on the stability of the daughter ion. In the MD spectra of the ions formed in several stages, to characterize the generality of the breakdown reactions, in addition to the intensities of the MPs, the accurate positions of their maxima and the general shape of the curve are important. 相似文献
9.
The mass spectra of 1,2-diphenyl-pyrazolidine-3,5-dione and twenty-one 4-substituted derivatives are reported. Their fragmentation patterns have been studied by deuterium labelling, exact mass measurements, metastable studies by the defocusing technique and low energy spectra. Hydrogen rearrangements from the 4-position of the heterocycle and/or from the ß-position of the 4-substituent groups, lead to the main primary fragment ions [C12H11N2]+ (m/e 183) as shown by the metastables. The 4,4-d2 derivative shows an appreciable isotope effect even for molecular ions decomposing in the ion source. By comparison with the metastable abundances of competitive reactions, the molecular ions (m/e 252) of the 4-unsubstituted compound appear to be structurally different from the corresponding m/e 252 fragment ions formed from 4-derivatives by the loss of 4-substituent with H rearrangement. If only vinylic or aromatic hydrogen atoms are present, primary cleavage of the heterocyclic ring occurs with loss of OH·, C3O2 and C3HO2. Important rearrangements leading to elimination of C6H6N and C6H7N are typical for unsaturated substituents on position four having allylic hydrogen atoms. Fragment ions, identical to molecular ions of some compounds discussed here, are obtained by electron-impact and/or thermal decompostion of some complex compounds containing more than one 1,2-diphenyl-pyrazolidine-3,5-dione system. The [C6H5N2]+ (m/e 105) and [C6H5]+ (m/e 77) ions are common fragments of all the title compounds. Any hydrogen scrambling reactions between phenyl and heterocycle or 4-substituent groups can be excluded. 相似文献
10.
E. Constantin F. H. Kotzyba-Hibert J. M. Lehn P. Traldi 《Journal of mass spectrometry : JMS》1987,22(1):13-16
Mass spectra of some macropolycycles have been studied. Normal and metastable (B/E) mass spectra are presented. The fragmentation patterns and the structures of the main ions are discussed. 相似文献
11.
Witold Danikiewicz Krzysztof Wojciechowski Roel H. Fokkens Nico M. M. Nibbering 《Journal of mass spectrometry : JMS》1993,28(8):853-859
The electron impact-induced fragmentation patterns of 2,1-benzisothiazoline 2,2-dioxide nitro derivatives were studied. The rationalizations proposed for the fragmentations are supported by accurate mass measurements, daughter ion (mass analysed ion kinetic energy and B/E linked-scan), parent ion, and constant neutral loss spectra in metastable and collision-induced dissociation modes and deuterium labelling. 相似文献
12.
Substituted benzeneboronic acids are important intermediates in the synthesis of support matrices for affinity chromatography but their analysis by mass spectrometry is hindered by thermal reactions in the ion source. A simple derivatization with 1,2- or 1,3-diols removes this difficulty and imparts sufficient volatility for application of gas chromatography/mass spectrometry. The mass spectra of the resulting boronate esters are discussed with reference to high resolution measurements, isotope labelling studies and observation of metastable ions. ortho Substituents are shown to interact strongly during fragmentation. Linked scanning at constant B/E was used to characterize fragmentation pathways and the compatibility of linked scanning and GC/MS is reported. 相似文献
13.
The isomerization of the molecular ions of ethylbenzene, 7-methylcycloheptatriene and p-xylene by skeletal rearrangement prior to the formation of [C7H7]+ ions has been investigated by using 13C labelled compounds. The results obtained for ions generated by 70 eV and 12 eV electron impact, and fragmenting in the ion source, the 1st field free region and the 2nd field free region, respectively, are compared with those obtained from D labelled derivatives. It is shown that at long reaction times metastable p-xylene ions lose a methyl radical after scrambling of all C atoms and H atoms, while the unstable molecular ions in the ion source react by specific loss of one of the methyl substituents. Both unstable and metastable ethylbenzene ions fragment by two competing mechanisms, one corresponding to specific loss of the terminal methyl group, and the other involving scrambling of all C and H atoms. These results are discussed by use of a dynamic model developed for the mutual interconversion and fragmentation of the molecular ions of ethylbenzene, methylcyclo-heptatriene and p-xylene. The experimental results can be explained by an equilibrium between metastable methylcycloheptatriene ions and p-xylene ions with sufficient energy for skeletal rearrangement, while about 40% of the metastable ethylbenzene ions fragment after rearrangement to methylcycloheptatriene ions and about 60% of the ethylbenzene ions rearrange further to xylene ions before fragmentation. Metastable methylcycloheptatriene ions, mainly lose a methyl group without a skeletal rearrangement, however, because the rearranged ions are kinetically trapped as ‘stable’ xylene ions or ethylbenzene ions. 相似文献
14.
Zaharie Moldovan Nicolae Palibroda Victor Mercea Gheorghe MihÎilescu Maria Chiriac Mircea Vlasa 《Journal of mass spectrometry : JMS》1981,16(5):195-198
This paper presents low and high resolution mass spectra as well as fragmentation processes under electron impact for methyl, ethyl and propyl-pivaloyl acetate. The fragmentation patterns have been established using elemental compositions of ions determined by high resolution, metastable transitions and deuterium labelling. 相似文献
15.
W. D. Weringa 《Journal of mass spectrometry : JMS》1971,5(9):1055-1072
The mass spectral fragmentations of three spiro-undecanones and four dispiro-hexadecanones with six-membered rings, and of two spiro-nonanones with five-membered rings are recorded and discussed. The fragmentation patterns for the spiro[4,4]nonanones and the spiro[5,5]undecanones have been determined by using specific deuterium labelling and in some cases the measurement of metastable transitions by the defocusing technique. The most important fragment ions in the spectra of four dispiro-hexadecanones could be explained by assuming the same types of fragmentation as found for the monospiro-ketones. The composition of the fragment ions has been checked by high resolution mass measurements. 相似文献
16.
The electron-impact-induced ionization and fragmentation of six C6H10 structural isomers have been studied in order to determine the effect of isomerism upon their mass spectrometric behavior. The 70 eV mass spectra, metastable transitions and appearance potentials of the principal ions are reported. Significant differences between the mass spectra of the six isomers were observed; however, metastable transition and appearance potential data indicate that the fragmentation path-ways are the same for all the C6H10 molecules. Experimentally determined ionization potentials for the structural isomers are presented and compared to ionization potentials calculated by the bond orbital method. Utilizing fragmentation pathways deduced from general features in the mass spectra and from observed metastable transitions, we calculated heats of formation (ΔHf) for the observed principal ions and compared these values to ΔHf values for isomeric ions from other molecules. 相似文献
17.
G. Holzmann B. Krieg H. Lautenschlger P. Konieczny 《Journal of heterocyclic chemistry》1979,16(5):983-991
The mass spectra of a variety of alkyl- and aryl-4-imidazolin-2-ones have been determined and the fragmentation mechanisms have been analyzed by deuterium labelling, high resolution and metastable transitions allowing certain differentiations of positional isomers. In contrast to the benzoid systems the mass spectra of isomeric alkyl-4-imidazolin-2-ones are distinctive. The influence of the position of substituents is demonstrated by phenyl-4-imidazolin-2-ones establishing an exact prediction of fragmentation pathways. Fragment ions (e.g. [M-HNCO].+) which are the result of rearrangement processes were excluded for structure determinations. The ion structures involved were elucidated by collisional activation comparing model ions. Alkyl-phenyl-4-imidazolin-2-ones give almost identical mass spectra, but the positional isomers can easily be distinguished by different fragmentation patterns in both metastable and collisional activation spectra of the molecular ions. 相似文献
18.
It has been established that the loss of ketene from the molecular ions of 2-acetamidobenzothiazole and 2-acetamidobenzimidazole proceeds via a four centre mechanism and gives the corresponding 2-amino-benzazole. For metastable ions with low energy and a long lifetime, hydrogen scrambling occurs before fragmentation through departure of HNC from the 2-aminobenzazole. A mechanism is proposed. 相似文献
19.
The mutual interconversion of the molecular ions [C5H6O]+ of 2-methylfuran (1), 3-methylfuran (2) and 4H-pyran (3) before fragmentation to [C5H5O]+ ions has been studied by collisional activation spectrometry, by deuterium labelling, by the kinetic energy release during the fragmentation, by appearance energles and by a MNDO calculation of the minimum energy reaction path. The electron impact and collisional activation mass spectra show clearly that the molecular ions of 1–3 do not equilibrate prior to fragmentation, but that mostly pyrylium ions [C5H5O]+ arise by the loss of a H atom. This implies an irreversible isomerization of methylfuran ions 1 and 2 into pyran ions before fragmentation, in contrast to the isomerization of the related systems toluene ions/cycloheptatriene ions. Complete H/D scrambling is observed in deuterated methylfuran ions prior to the H/D loss that is associated with an iostope effect kH/kD = 1.67–2.16 for metastable ions. In contrast, no H/D scrambling has been observed in deuterated 4H-pyran ions. However, the loss of a H atom from all metastable [C5H5O]+ ions gives rise to a flat-topped peak in the mass-analysed ion kinetic energy spectrum and a kinetic energy release (T50) of 26 ± 1.5 kJ mol?1. The MNDO calculation of the minimum energy reaction path reveals that methylfuran ions 1 and 2 favour a rearrangement into pyran ions before fragmentation into furfuryl ions, but that the energy barrier of the first rearrangement step is at least of the same height as the barrier for the dissociation of pyran ions into pyrylium ions. This agrees with the experimental results. 相似文献
20.
The metastable transitions in the mass spectra of 21 lycoctonine bases have been studied by the method of metastable defocusing (MD). It has been established that as a criterion of the monotypicity of single-stage fragmentation reactions it is possible to use a linear dependence of the relative intensities of the metastable peaks (MPs) on the stability of the daughter ion. In the MD spectra of the ions formed in several stages, to characterize the generality of the breakdown reactions, in addition to the intensities of the MPs, the accurate positions of their maxima and the general shape of the curve are important.Institute of the Chemistry of Plant Substances, Academy of Sciences of the Uzbek SSR, Tashkent. Translated from Khimiya Prirodnykh Soedinenii, No. 4, pp. 481–495, July–August, 1984. 相似文献