共查询到20条相似文献,搜索用时 128 毫秒
1.
Jacques Delaunay Alain Lebouc Olivier Riob 《Magnetic resonance in chemistry : MRC》1979,12(5):278-281
The 1H NMR study of 2-alkyl-3-chlorotetrahydropyrans, obtained by reaction of Grignard reagents with a mixture of cis/trans-2,3-dichlorotetrahydropyrans, shows cis/trans configuration of two isomers in which the alkyl substituents are exclusively in the equatorial position. 3-Chloro-2-phenyltetrahydropyran exists in trans (eq-eq) configuration only. The 1H NMR study of cis/trans 2-alkoxy (or aryloxy)-3-chlorotetrahydropyrans, obtained by reaction of alcohols or phenol with 2,3-dichlorotetrahydropyrans, shows the axial position of the alkoxy (or aryloxy) substituent. 相似文献
2.
R. Faure J. Elguero E. J. Vincent R. Lazaro 《Magnetic resonance in chemistry : MRC》1978,11(12):617-627
The 13C NMR spectra of 43 benzothiazoles have been recorded in DMSO-d6. All carbon atoms have been attributed in an unambigous way owing to substituent effects in position 4, 5, 6 or 7. We discuss variations of chemical shifts as a function of the nature of the substituent in position 2 (equation of type: Δδ = aF+bR+cQ+d′), annelation in the benzoheterocyclic series, and prototropic tautomerism in the benzothiazolic series (in the case of the substituent in the 2-position being an OH, SH or NHR group). 相似文献
3.
Roger Petiaud Quang Tho Pham 《Journal of polymer science. Part A, Polymer chemistry》1985,23(5):1343-1360
A microstructure analysis of polychloroprenes by 1H and 13C NMR produced slightly different results which, however, are in good agreement. The main uncertainty concerned the assignment of the 1,4-cis and trans head-to-head and tail-to-tail additions. In the (+ 12, +70°C) region of polymerization temperatures the principal addition mode was 1,4. An increase in the polymerization temperature to 70°C increased the abnormal head-to-head, tail-to-tail additions, and 1,4-cis additions (6–7%), and all vinyl structures that were not higher than 2–3% were equally distributed between 1,2 and 3,4. Under the experimental conditions used in this study no isomerized vinyl structures were found. As in all radical polymerizations the influence of temperature on the propagation mechanisms, namely, the addition modes, was relatively weak, but because of the great number of possible addition modes in microstructure—physicomechanical relationships variations in the microstructure must be taken into account. Only 1H and 13C NMR are capable of determining these variations quantitatively. 相似文献
4.
The 13C NMR spectra of all trans-styryldiazines, methyldiazines and trans-styrylpyridines have been fully assigned. Empirical shift increments were obtained for the chemical shifts of the carbon atoms; these are discussed in the light of theoretical considerations. 相似文献
5.
Benzothiazolinic spiropyrans, merocyanines and photomerocyanines, thermally stabilised to a high degree, have been studied by means of Fourier transform 1H and 13C NMR. The results show the polarity of open forms such as merocyanines and photomerocyanines, their trans configuration, the alternation of the electronic density on the dimethine bridge between the ‘benzothiazolinic’ and ‘phenolate’ part of these molecules, and also a favoured configuration when photomerocyanines have an alkoxy or aryloxy group on the 3 position. 相似文献
6.
From a carbon magnetic resonance study of several alkylcobaloximes RCo(DMG)2B (DMG = dimethylglyoximate monoanion), it was possible to estimate the α, β and γ effects of the Co(DMG)2B group on the chemical shifts of the carbon atoms of various alkyl groups R. The chemical shifts of the carbon atoms belonging to the equatorial ligands and to the axial base B are not significantly affected by structural modification of the R groups. Values of δ in benzylcobaloximes XC6H4CH2Co(DMG)2B agree with a donor effect of the ? CH2Co(DMG)2B radical. Values of 1J(13C? H) coupling constants, measured in 13C enriched methylcobaloximes, do not vary appreciably when B is changed (J(13C? H) = 137 ± 1 Hz) and are close to the value obtained for methylcobalamine. 相似文献
7.
The loss of methane and ethylene in the mass-spectrometric fragmentation of different isomeric butyl ions which originate from butyl halides has been studied. The different carbon atoms in n-butyl are already equivalent after 10?7 s, whereas the statistical distribution of the hydrogen atoms within the molecule can only be observed for the metastable peaks. A protonated cyclobutane structure is proposed as an intermediate product in the fragmentation of the n-butyl ion. The fragmentation of this model has been simulated by a computer. This allows prediction as to the time-scale of fragmentation. The comparison of this model fragmentation with that of isomeric butyl ions shows that, even in the decay of the tertiary butyl ion, the formation of the proposed rearranged cyclic structure competes favorably with the direct fragmentation. 相似文献
8.
James Bouquant Josselin Chuche Odile Convert Bernard Furth 《Magnetic resonance in chemistry : MRC》1979,12(1):5-11
The configuration of various bicyclo[4.2.0]octanols has been established by 1H NMR spectroscopy, with Eu(dpm)3 as shift reagent. The intrinsic parameters Δ and K have been obtained and used as structural probes. Moreover, detailed data analysis showed that, contrary to the generally accepted concept, the vicinal coupling constant between trans cyclobutanic protons can be larger than that between cis protons. The chemical shifts obtained by 13C NMR spectroscopy are consistent with the proposed structures. The results have been extensively used to determine unambiguously the configuration of tricyclo[6.4.0.02,7]dodecanols and tricyclo[5.4.0.02,6]undecanol. 相似文献
9.
Claude Moulis Edouard Stanislas Jean-Claude Rossi 《Magnetic resonance in chemistry : MRC》1978,11(8):398-400
The four pseudoprotoberberins extracted from Isopyrum thalictroides L. were reduced with sodium borohydride to the corresponding tetrahydropseudoprotoberberins. Comparison between the 13C NMR spectra of these and of synthetic protoberberins allowed us to assign a trans-1 configuration to the four reduced alkaloids and also to provide for this particular configuration an unequivocal criterion for the differentiation (based on the chemical shift of C-8) between tetrahydroprotoberberins (9, 10 substituted) and tetrahydropseudoprotoberberins (10, 11 substituted). 相似文献
10.
J. Courtieu Y. Gounelle P. Gonord S. K. Kan 《Magnetic resonance in chemistry : MRC》1974,6(3):151-154
The NMR spectrum of acrolein and acroyl fluoride (CH2?CH? COX with X?H and F) oriented in a nematic phase has been measured and information about conformational equilibrium s-cis ? s-trans has been obtained. The barrier to internal rotation of the COX group has been studied with various hypotheses. Good agreement between experimental and calculated spectra has been obtained using the potential equation V(?) = ΣnVn(1 – cos n?)/2, with V1 = ?200 cal mol?1, V2 = 1500 cal mol?1 and V3 = 400 cal mol?1 for the fluorine compound, and V1 = 1200 cal mol?1, V2 = 3000 cal mol?1 and V3 = 2000 cal mol?1 for acrolein; this last compound is found to be mostly in the s-trans conformation. 相似文献
11.
R. Faure J.-P. Galy E.-J. Vincent J. Elguero 《Magnetic resonance in chemistry : MRC》1977,10(1):249-250
The signals of protons bonded to carbon atoms in α position to the pyridinic nitrogen atom in thiazole and in γ position in thiazolo[2,3-e]tetrazole are broadened. This broadening disappears on irradiation at the 14N resonance frequency, on cooling, and in an acidic medium (in which the protonation sites in both molecules can be determined). 相似文献
12.
Microstructures of 1,2-trans-and 1,4-trans-poly(penta-1,3-dienes) synthesized using different catalysts were determined by high resolution 13C NMR spectroscopy. The content of dyad combinations of the 1,4-and 1,2-structures was quantitatively determined in hydrogenated
poly(penta-1,3-dienes) from the ratio of intensities of the characteristic signals of the carbon atoms of the methylene groups
in the 13C NMR spectra.
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1113–1118, June, 2007. 相似文献
13.
The four isomeric 3-dimethylamino-trans-2-decalols-1,1,4,4-d4 have been synthesised. Examination of PMR spectra of these compounds allows us to confirm the ‘flattened-chair’ conformation for the cis N(CH3)2a OHe isomer, whereas the remaining three conserve the double chair conformation. The same type of flattening is also observed in the case of the diaxial quaternary ammonium salt and is even more marked in the cis N(CH3)3a OHe isomer resulting in a ‘twist-chair’ conformation. 相似文献
14.
Guy Pouzard Michel Rajzmann Hubert Bodot Louis Pujol 《Magnetic resonance in chemistry : MRC》1973,5(5):209-214
Proton–proton 3J, 4J and 5J NMR coupling constants have been calculated for cyclohexane and monosubstituted cyclohexane conformers (substitiuents: Li, CH3, OH, F) by the two methods mentioned. Comparing the two methods on the basis of group theory, we show the necessity to use the second. The results from this method are compared with those of the literature. 相似文献
15.
Studies in Stereochemistry XIV. Diels-Alder adducts in the resin series; action of peracids and acid-catalysed ring opening of epoxides The synthesis of Diels-Alder compounds of type 2 with a 17-nor-13(14)-atisène skeleton is described (cf. Schemes 1–3). Depending on the nature and configuration of substituents R1 and R2 on the carbon atoms 15 and 16, an epoxide ( 24–33 ) or a ketone ( 35–38 ) or a mixture of epoxide, ketone and lactone is obtained by the action of p-nitroperbenzoic acid on the double bond of these adducts (cf. Scheme 4). A simplified reaction scheme is suggested to explain the formation of the various products. In an acid-catalysed reaction, the epoxides isomerize mainly into ketones. Nevertherless, in some cases, dienes (e.g. 52 ) or hydroxy-γ-lactones of (13R*, 14S*)-configuration (e.g. 50 ) resulting from the opening of the epoxide ring with retention of configuration were obtained. 相似文献
16.
Ronald Lafrance Jean-Pierre Aycard Jeanne Berger Hubert Bodot 《Magnetic resonance in chemistry : MRC》1976,8(2):95-101
The 1H NMR spectra of a series of cis and trans-3R,4 X-cyclohexanones (-2,2,6,6-d4) are analysed. By comparison of their 3J coupling constants with those of cyclohexane homologues we obtain information about the chair–chair equilibrium constants for R = CH3, X = CN, the chair structure of cis isomers with an equatorial t-butyl group, and a conformational heterogeneity with trans (CH3)3C and CN groups. This latter situation is analysed by means of a simplified but controlled Karplus relationship, on the basis of a mixture of two conformers; this involves a diequatorial chair and a boat form with a dihedral angle Φ34 of about ?6°. 相似文献
17.
The conformation in solution of several unsatured sugars of the general type XHC?CH—glycosyl has been studied by NMR. In the trans series, the population of the sterically permitted gauche conformer increases with the M-ability of X. In the cis series, the population of the trans conformer increases with the space requirements of X. These phenomena are discussed. 相似文献
18.
A 13C NMR study of a series of methyl sulphur compounds is described. The results are discussed in terms of the deshielding effects on the methyl carbon exerted by –SH, –SMe, –SSMe, –SSEt, –SSMe, –SC(O)Me, –SC(S)Me, –SC(S)SMe. The 13C NMR chemical shifts of a series of S-methyl thioesters and dithioesters are compared with corresponding esters and connected with chemical properties. 相似文献
19.
The 13C- and 17O-chemical shifts of 31 aliphatic ethers are measured and discussed. The 17O-chemical shifts of the ethers ROR′ correlate with chemical shifts for the methylene groups of the corresponding alkanes RCH2R′. The constant of proportionality can be related to the orbital expansion term 〈r?3〉2p. The δc for carbon atoms can also be correlated with δc for the corresponding alkanes. The origin of the correlation is discussed taking into account the conformational modifications resulting from introduction of an oxygen atom in an alkyl chain. 相似文献
20.
Novel types of sugars bearing three nitrogen atoms: triazenes and 2-phenylimino-1, 3, 4-oxadiazoles . A series of aminodeoxysugars treated with p-nitrobenzenediazonium tetrafluoroborate led to the corresponding triazenes, each of which in chloroform solution existing as an equilibrium between its two tautomeric forms. The free energy of activation of the exchange of the proton between the two nitrogen atoms has been estimated by variable temperature 1H-NMR. measurements. Each triazenylsugar gave on acetylation an unique positional isomer bearing its acyl group on the nitrogen atom directly attached to the glycosyl group. Phenylsemicarbazones of two keto-sugars were oxidized with El Khadem's reagent (I2, HgO, MgO) to give the corresponding spiro-2-phenylimino-1, 3, 4-oxadiazoles. 相似文献