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1.
Bikau Shukla Akira Miyoshi Mitsuo Koshi 《Journal of the American Society for Mass Spectrometry》2010,21(4):534-544
The role of methyl radicals in the networking of sp2 carbons has been explored through kinetic analysis of mass spectra of the gas-phase products of the pyrolysis of toluene
and toluene/acetone mixtures. Pyrolytic reactions were performed in a flow tube reactor at temperatures of 1140–1320 K and
a constant total pressure of 10.38 Torr with a residence time of 0.585 s. On addition of acetone, methyl substituted products
and their derivatives were enhanced. Mass peaks were observed in several sequences at an interval of 14 mass units; these
ions correspond to methyl substituted products formed as a result of hydrogen abstraction (−H) followed by methyl radical
addition (+CH3). Each major peak was usually preceded by a peak at two mass units lower, which was likely produced through dehydrogenation/dehydrocyclization
(−H2) of methyl substituted products. Detected species include a large number of alkyl, cyclotetrafused (CT), cyclopentafused
(CP) mono-, di-, and polycyclic aromatic hydrocarbons (PAHs) along with primary PAHs. The analysis showed that MAC (methyl
addition/cyclization) has a unique capacity to induce the sequential growth of hexagonal networks of sp2 carbons from all fusing sites [1] of a PAH. Moreover, MAC was found capable of answering an important question in PAH growth,
which is expansion of the CT → CP → hexagonal network for which other reported mechanisms are inefficient. 相似文献
2.
The 13C NMR spectra of a series of methyl substituted 3-arylpiperidines and 4-aryl-4-piperidinols and related compounds are reported, and chemical shift data analysed in terms of the configuration and conformation of isomeric pairs. Special attention is given to the γ chemical shift parameter of axial methyl, and the effects of a nitrogen lone pair orbital and hydroxyl or acyloxy group on the chemical shifts of ring and methyl carbons. 相似文献
3.
Sophia Mitkidou Stelios Papadopoulos Julia Stephanidou-Stephanatou 《Journal of heterocyclic chemistry》1991,28(6):1497-1499
The 1H and 13C nmr chemical shifts are used for the structural assignment of isomeric 1-aroyl-4,5-dihydro-5-hydroxy-4,4-dimethyl-1H-pyrazoles 1 unsymmetrically substituted with phenyl or methyl in the 3,5-positions of the pyrazole ring. The 1H nmr spectra of 1-aroyl- or 1-acetyl-4-methyl-1H-pyrazoles 2 are useful in structure elucidation of unsymmetrically 3- or 5-methyl substituted derivatives. 相似文献
4.
Kazunori Sakata Junichi Yamashita Mamoru Hashimoto Akihiko Tsuge Yasuhiro Tanoue 《Journal of heterocyclic chemistry》2001,38(4):933-938
The diazo coupling reaction between a tetraaza[14]annulene ( 1 ) and a series of 4‐substituted phenyl‐diazonium tetrafluoroborates yielded the corresponding 7, 16‐disubstituted products. Mass spectra indicate the presence of molecular ion peaks that substantiate the 7,16‐disubstituted products ( 4 ); the lack of olefinic proton signals corresponding to the 7,16‐ position in the 1H nmr spectra of 4 also show that diazo coupling has taken place. Analysis of signals corresponding to the methyl groups of 4 in their 1H and 13C nmr spectra indicate that the imine‐bis‐hydrazone form is present for compounds that do not contain p‐methoxyphenyl groups. However, analysis of methyl signals in the nmr specta of compounds 4 containing p‐methoxyphenyl groups show that the bis‐azo form and the imine‐bis‐hydrazone form are present through tautomerism. Complexation with nickel(II) ion induces the formation of the bis‐ azo structure. 相似文献
5.
13C n.m.r. spectra of a number of methyl substituted cyclohexanes, some of them conformationally homogeneous, have been recorded in CDCl3 and used to determine shift effects engendered by the introduction of methyl groups on carbon atoms remote from the site of substitution. Sizeable changes in shifts are found, including a substantial effect of an equatorial methyl group on an axial methyl group δ to it (+0.67 ppm, ‘δea’). The effects reported are of consequence in investigations of conformational problems by 13C n.m.r. techniques. 相似文献
6.
7.
Giovanna Barbarella Pasquale Dembech Anna Garbesi Antonino Fava 《Magnetic resonance in chemistry : MRC》1976,8(9):469-476
13C n.m.r. spectra of methyl substituted thianes and thianium cations have been determined. The magnitude of the 13C substituent effects of an equatorial methyl group or of a gem-dimethyl grouping appear to depend in a systematic way on whether the carbon atom concerned is adjacent to, or removed from, the heteroatom. The shieldings are discussed in relation to the conformational properties of the thiane ring. Moreover, the average 13C substituent parameters obtained from conformationally biased systems are applied to potentially mobile systems to assess the position of the conformational equilibrium. 相似文献
8.
The vicinal couplings of ring hydrogens to methyl C atoms (3JCH3H) in 22 methyl substituted non-benzenoid polycyclic conjugated hydrocarbons have been determined from the undecoupled 13C NMR spectra and have been correlated with bond lengths as well as with the corresponding vicinal H,H couplings, which are taken partly from own 1H NMR analysis and partly from literature. As a result the (3JCH3H) couplings of sterically unperturbated methyl groups in 7-membered rings are proportional to the corresponding 3JHH values which is indicative of comparable influences, but both types of vicinal couplings are not dependent on bond lengths only. Moreover they are to a large extent determined by the CCH bond angles θ and θ', which show a significant variation in condensed 7-membered rings so that this twofold dependence has to be taken into account for structure determinations. 相似文献
9.
The mass spectra of six cis-trans isomeric 1,2,3,4-tetramethylcyclohexanes are discussed. The intensity ratio of [M? CH3]+/[M? C2H5]+ correlates with the strain energies of the stereoisomers. Therefore, the identification of cis-trans isomers is possible by means of their mass spectra. The mass spectra of deuterium labelled compounds demonstrate favoured fragmentation of the axial methyl groups and ring opening between the cis substituted carbon atoms of the cyclohexane. 相似文献
10.
The isolation and characterisation of methyl piperitol, (+)-epieudesmin and (+)-episesamin from the stem bark of Zanthoxylum acanthapodium is reported. The 1H and 13C NMR spectra are correlated with those of other known lignans and it is shown that 13C NMR shifts can be used to assign unambiguously the nature and configuration of the aryl groups in unsymmetrically substituted 2,6-diaryl-3,7-dioxabicyclo[3.3.0]octanes. Other less satisfactory methods which have in the past been used for this purpose are discussed and in particular the use of coupling constants to assign stereochemistry in this series is strongly criticised. Revised structures for pulviatilol, methyl pluviatilol (fargesin) and xanthoxylol are proposed. 相似文献
11.
13C- and 1H-NMR. spectra of ortho-benzoquinone 1 and its methyl derivatives have been analysed. By means of heteronuclear double resonance experiments it is shown that assignments given in the literature for the olefinic carbon resonances of 1 and of a series of substituted ortho-benzoquinones have to be inverted. 13C-carbonyl frequencies of various six-membered cyclic ketones are presented. 相似文献
12.
Mowafak Y. Shandala Mikdad T. Ayoub Moyayed J. Mohammad 《Journal of heterocyclic chemistry》1984,21(6):1753-1754
A series of substituted 4-aminobut-2-enolide derivatives have been synthesized by reaction of a variety of substituted amines with methyl tetronate. The 1H and 13C nmr spectral analysis of all compounds synthesized are given. 相似文献
13.
James Gainer Graham A. Howarth William Hoyle Stanley M. Roberts 《Magnetic resonance in chemistry : MRC》1976,8(4):226-227
13C n.m.r. spectra of some substituted isoxazoles have been examined to ascertain the reactive site in the metallation of 4-substituted 3,5-dimethylisoxazoles. The results obtained indicate that metallation occurred exclusively at the C-5 methyl. 相似文献
14.
J. Schraml V. Chvalovský M. Mägi E. Lippmaa R. Calas J. Dunoguès P. Bourgeois 《Journal of organometallic chemistry》1976,120(1):41-47
29Si and 13C NMR spectra of trimethylsilylbenzenes substituted at different positions by methyl and trimethylsilyl groups were investigated with special reference to steric interactions between the ortho-substituents. The steric effects, as measured by 13C and 29Si chemical shifts, are generally smaller in trimethylsilyl- than in t-butyl-substituted compounds. Both nuclei follow the same general trends in the benzene derivatives. 相似文献
15.
The 1H NMR spectra of a series of substituted 1,5-benzodiazepines and thiazepines are analysed by the LAOCN3 fitting program. The saturated molecules appear to exist in puckered chair conformations. The effect of increasing methyl substitution is a reduction in the amount of puckering with a flattening of the chair. Symmetrical substitution of the heterocyclic rings allows a ready inversion at room temperature whereas asymmetrical substitution stabilises the least hindered conformation. Variable temperature measurements are reported. 相似文献
16.
17.
Ernest L. Eliel Muthiah Manoharan K. Michal Pietrusiewicz Karl D. Hargrave 《Magnetic resonance in chemistry : MRC》1983,21(2):94-107
The 13C NMR spectra of 62 oxanes (tetrahydropyrans) with and without methyl substituents at various ring positions, some of them bearing in addition (or instead) ethyl, vinyl, ethynyl, carbomethoxy and methylol substituents at C-2, have been recorded, and the 294 resulting chemical shifts have been correlated by multiple linear regression analysis. Axial and equatorial α-, β-, γ-, δ-, gem- and vic-parameters for shifts caused by methyl groups at all ring positions, and similar parameters for Et,—CH?CH2,—C?CH, CO2Me and CH2OH groups at C-2, are reported. Standard deviations of the parameters are, in most cases, within 0.3 ppm and the agreement of calculated and experimental shifts is excellent. This is probably the largest parameter set of this type extant. 13C NMR spectra of a number of additional substituted tetrahydropyrans, and of 3,6-dihydro-2H-pyrans and 3,4-dihydro-2H-pyrans, are tabulated and discussed. 相似文献
18.
Nelson L. C. Domingues Paulo R. Olivato Adriana K. C. A. Reis Mirta G. Mondino Filipe S. Lima Roberto Rittner 《Magnetic resonance in chemistry : MRC》2009,47(3):270-272
The complete assignment of the 1H and 13C NMR spectra of the diastereomeric pairs of some α‐arylsulfinyl‐substituted N‐methoxy‐N‐methylpropionamides with the substituents methoxy, methyl, chloro, nitro is reported. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
19.
13C NMR spectra of unsubstituted 1,6,6aλ4-trithiapentalene and a series of methyl and phenyl substituted 1,6,6aλ4-trithiapentalenes have been recorded. The spectra have been assigned by comparison with 1H NMR data based on coupling constants from undecoupled spectra. From the chemical shift of C-3a it is concluded that the double bond character of the C-3a—S-6a is low. The relaxation times for C-2 and C-3 only show small differences; this seems not to be in favour of a fast interconversion between two thiocarbonyl forms. The NMR data obtained seem thus to be in accordance with a bicyclic naphthalene-like structure with ten delocalised π-electrons. 相似文献