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1.
The 13C NMR spectra of 2-dimethylaminocyclohexanols and the four trans-3-dimethylamino-2-decahydronaphtols are described. The gauche interactions allow precise estimation of chemical shifts for each carbon atom; thus, band attribution can be resolved without mistake. In the case of the cis and the trans diequatorial compounds, the conformational perturbations which we have suggested before are verified by our present measurements on the substituted carbon atoms. We also show effects on adjacent atoms, which were unobservable with the usual IR and 1H NMR techniques. 相似文献
2.
Christiane Blanchard Jean-Marc Fabre Claude Montginoul Brat Ali Chaffia Eliane Torreilles Louis Giral 《Journal of heterocyclic chemistry》1978,15(1):149-153
The results of nucleophilic substitution of the 2-methoxy-9-acridone are discussed in terms of competition between both ionic sites N? and O?, of the molecule. They are the first examples of O-alkylation of substituted 9-acridone. 相似文献
3.
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
4.
Some furochromenes substituted at the 2-position by an electron-attracting group were obtained starting from ortho-hydroxyformyl derivatives of 2,2-dimethyl-2H-chromene following various processes which are indicated. These new furochromenes are pharmacochemical analogues of some natural pyranocoumarins, and as such they are potential photosensitizers. 相似文献
5.
Jean-Pierre Albrand Didier Gagnaire Jean Martin Jean-Bernard Robert 《Magnetic resonance in chemistry : MRC》1973,5(1):33-41
The proton NMR spectral analysis of eight different 1,3,2-dithiaphospholanes with various groups attached to the phosphorus atom has been performed. The AA′BB′X (X phosphorus atom) system shows that the two 3J(P? S? C? H) coupling constants have a small magnitude and opposite signs. Using the 3J(HH) values, the torsion about the C4—C5 bond has been evaluated. The conformational requirements in the two isomers of the 2 phenyl-4-methyl-1,3,2-dithiaphospholane are also discussed. 相似文献
6.
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
7.
Saturnin Claude Raffaele Tabacchi Laurent Due Rudolf Fuchs Karl-Josef Boosen 《Helvetica chimica acta》1980,63(3):682-692
Study of Electron-Impact Fragmentation of Benzothiazole Derivatives The mass spectra of eighteen substituted benzothiazoles are reported and discussed. All these compounds are thermodynamically stable and give an intense molecular ion, which undergoes different types of fragmentation depending on the nature of the substituent which is rarely eliminated directly. β-Cleavage with respect to the heterocyclic double bond is often observed. Specific 2H-, 13C-, 15N- and 34S-labelling have been used in order to confirm the fragmentation patterns. 相似文献
8.
R. Faure E.-J. Vincent G. Assef J. Kister J. Metzger 《Magnetic resonance in chemistry : MRC》1977,9(12):688-694
We have recorded the 13C n.m.r. spectra of thiones and thioethers in the 1,3-diazole and 1,3-diazine series with various alkyl substituents at the nitrogen atoms. Some analogous oxygen containing heterocycles were also examined. We have shown that in the thiocarbonylated compounds the thiol ? thione equilibrium is displaced towards the thione form, but that 13C n.m.r. gives only qualitative results. In the sulphur containing derivatives the isopropyl group is in a fixed conformational position because of the steric hindrance of the sulphur atom. Substitution by a tert-butyl group leads to unexpected γ values. We ascribe this phenomenon to ring deformation or to variations in the valence angles of the substituted nitrogen atoms. 相似文献
9.
C. Jaureguiberry M. C. Fournie-Zaluski B. Roques S. Combrisson 《Magnetic resonance in chemistry : MRC》1973,5(4):165-168
α-formylpyrroles substituted on the nitrogen atom by groups of increasing steric hindrance show no significant modification in the value of their stereospecific 5J coupling constants. In the i.Pr-1 and s.Bu-1 formyl-2 pyrroles, the existence of a preferential conformation has been shown. Studies of rotational barriers indicate a twist only for the t.Bu-1 formyl-2 pyrrole molecule. The stability of the 5J value relative to this last compound is attributed to a relay of the σ—σ mechanism by a σ—π transmission. 相似文献
10.
Emile Rouvier Raphaël Pastor Jean Musso Aim Cambon 《Magnetic resonance in chemistry : MRC》1974,6(12):640-643
In this paper we report the conformational analysis of several di- or trisubstituted ethanes substituted by the following groups: N-dialkly, thioalkyl, alkoxy, N-pyrrolidino, N-benzyl, nitrile or carbomethoxy. Spectra were calculated by a method based on chemical shifts. Relative stabilities of rotamers were discussed in relation to structural parameters (geometrical and electronic). 相似文献
11.
A study of the conditions of applicability to weak complexes of the relation log x = v log V + log (βv,cCc) = f(logV), where V and C are variable and constant total concentrations of the constituants of the complexe, shows that for conditions other than C ? V, another function φ(log V) accounts better for the formation equilibrium of the complexe. From f(log V) and φ (log V) a relation t(log V) is derived whose simple analysis permits the determination of the composition and the stability constant of weak complexes. Applications are given to 1:1, 1:2, 2:2 composition. 相似文献
12.
The NMR spectra of monochloro-, monobromo- and monofluoroacetone (CH3? CO? CH2X with X = Cl, Br, F) oriented in a nematic phase have been measured and the direct dipolar coupling constants determined. The barrier to internal rotation for the CH2F group has been studied for fluorine compound using various hypotheses. The best agreement with IR data has been obtained using the potential equation V(θ) = Σn Vn × (1 – cos nθ)/2 and a Boltzmann distribution of the CH2F group (V1 = 250 ± 50 cal.mol?1, V2 = 1650 ± 100 cal.mol?1, V3 = ?1000 ± 100 cal.mol?1). 相似文献
13.
Ronald Lafrance Jean-Pierre Aycard Hubert Bodot 《Magnetic resonance in chemistry : MRC》1977,9(5):253-259
For trans-3-R- and 5-R-1-acetoxy-4-cyanocyclohexene-6,6-d2 the molar fractions of diequatorial conformers are 0.83 (3-methyl), 0.68 (5-methyl), 0.57 (3-tert-butyl) and 0.55–0.69 (5-tert-butyl). For the last two compounds the values of the coupling constants are in agreement with the hypothesis of an ee?aa equilibrium. For the cis isomers, the molar fractions of equatorial alkyl conformers are 0.76 (3-methyl and 5-methyl) and 1.0 (3-tert-butyl and 5-tert-butyl). The cis-1-acetoxy-3-tert-butyl-4-methoxycarbonyl-cyclohexene presents a conformational heterogeneity. The conformational free energy of the methyl group in position 4 has been evaluated as ?0.6 kcal mol?1 (2.5 kJ mol?1). 相似文献
14.
Electrophilic Aromatic Substitution in Liquid Sulfur Dioxide. Kinetic Dependance of Rate on the Bromide Concentration and Influence of the Solvent during the Course of the Reaction On the reported data for bromination of anisole and eleven of its derivatives in liquid SO2, it was shown that, with a large excess of bromide, the rate of reaction, obeys a first-order law. Rate constants thus obtained do not discriminate between the two different forms of bromide, e.g. Br2 and Br?3 present as the A+Br?3 form, and corrections were made by use of the apparent equilibrium constant K′ for tribromide formation. The variations of rate constants with initial concentration of bromide has been studied and the effect results in a retardation of the bromination rate. Moreover, the ratio [Br2] [A+Br?]T, which is constant during an experiment, varies with initial bromide concentrations, this variation affecting the total rate. To account for the bromide effect on the reactivity, variations of ko,pg {1 + K′[A+Br?]T}VS[A+Br?]T were studied over a 0.01 to 1M range of bromide concentration. The mechanism proposed shows that liquid SO2 helps the reactive intermediate to be deprotonated and because of solvation of reactive species this step would probably be rate determining. Bromination by molecular bromine is more sensitive to substituent effects in liquid SO2 than in water. This result is ascribed to the +M effect of the methoxy group which increase the conjugation of ortho-substituted derivatives (p+p = ?7.83; p+o= ?10.47). 相似文献
15.
15N spectroscopy at natural abundance has been applied to the study of electronic delocalization in the N? C bond of a series of substituted anilines. The relationships which offer a good way for evaluating the extent of electronic delocalization from 15N chemical shift data in anilines have been extended to aminopyridines, aminopyrimidines and nucleosides. The results obtained for C? N bonds in the case of anilines and aliphatic enamines are consistent with those concerning amides and analogous compounds. The validity of ΔG≠-δ15N relationships for predicting π delocalization is discussed in terms of the relative contribution of δ- or π-density and non-bonded atom interactions to the total barrier height. 相似文献
16.
The orientation of the cycloaddition of diazomethane on unsaturated branchedchain sugars has been studied. For 3-C-cyanomethylidene-3-deoxy-1,2-O-isopropylidene-α-D-glycero-tetrofuranose the orientation was ‘normal’ and did not depend on the configuration at the double bond. The same situation prevailed with derivatives of 3-deoxy-1,2:5,6-di-O-isopropylidene-3-C-methylidene-α-D-xylo-hexofuranose. For the 3-C-acylmethylidene- and the 3-C-cyanomethylidene-3-deoxy-1,2:5,6-di-O-isopropylidene-α-D-ribo-hexofuranoses, the trans-(H–C(3′)–C(2))-isomer gave the ‘normal’ cycloadduct whereas the cis-isomer gave predominantly the αabnormal spiro-pyrazoline. This observation represents the first instance where the regioselectivity of a cycloaddition reaction is affected by the geometrical isomerism of the dipolarophile. The most probable explanation of the phenomenon is the conformational perturbation about the C(4)--C(5) bond of the unsaturated sugars induced by a change in the configuration at C(3). The consequence of that ‘conformational transmission’ of a difference in configuration at C(3) is that the steric crowding on the cis- than in the trans-isomer. Several novel examples of a new series of C-glycosylidenic derivatives, the spiro-pyrazolines, are described. 相似文献
17.
Robert Faure Jeanine Llinares Emile-Jean Vincent Jos Elguero 《Magnetic resonance in chemistry : MRC》1979,12(10):579-582
The 13C chemical shifts of 1-phenyl-2-pyrazoline and 25 N-nitrophenyl-2-pyrazolines, with different substituents on the heterocyclic ring, have been assigned. These values are discussed as a function of the steric and electronic nature of the various substituents. The steric effects produced conformational modifications, both in the nitrophenyl and 2-pyrazoline moieties, which explain some of the chemical shifts. 相似文献
18.
Jean-Claude Barrire Jeanine Clophax Stephan D. Gro Marc Vuilhorgne 《Helvetica chimica acta》1983,66(5):1392-1408
The cyclopentenecarbaldehyde 1a , acetals 2a , 2b and the cyclopentenone 2c have been transformed through regio and stereocontrolled reactions into a variety of enantiomerically pure substituted cyclopentanes. Using appropriately selected Wittig reagents, aldehyde 1a furnished the condensation products 3 , 4 , 5 . Michael addition of diethyl malonate on the α,β-unsaturated aldehyde 1a under phasetransfer conditions led efficiently to 7 . Reduction of the cyclopentenone 2c gave 21 in high yield. The cyclopentenes 2a , 2b and 23 , submitted to hydroboration-oxidation furnished the cyclopentanols 10 , 13 and 24 , respectively, in 30, 70 and 50% yields, reflecting the substitution pattern of the starting alkenes. The salient feature of these reactions is the stereospecificity due to the chiral centre of the molecules 1a , 2a , 2b and 2c , leading to compounds with two, three and four asymmetric centres. The straightforward synthesis of 11α-hydroxy-13-oxaprostanoic acid 20 is described and an approach towards the preparation of 9α, 11α-dihydroxy-13-oxaprostanoic acid 34 is also presented. The structure of these products has been determined by 1H- and 13C-NMR spectroscopy. 相似文献
19.
Deconjugation of sugars enones. Preliminary Communication Branched-chain sugar enones 1 and 2 ( R = Ac) deconjugated toposelectively (only the E isomers reacting) to 3 . The same phenomenon was noted in the case of Z- 4 which gave E- 5 . The kinetic parameters of these reactions favored a concerted mechanism, i.e. a [1, 5]-sigmatropic shift. 相似文献
20.
The NMR parameters are determined for a series of disubstituted (R = CH3, (CH3)3C; X = COOCH3, CN) and specifically deuterated cyclohexenes. The 3 J(HH), 3J(HD), 4J(HH) and 5 J(HH) coupling constants are used to evaluate the conformational equilibria. Three of the five compounds with an allylic t-butyl substituent, are conformationally heterogeneous; these equilibria, and those between stereoisomers are used for an analysis of this phenomenon, carried out within the framework of the hypothesis of additivity of conformational free energies and gauche interactions. 相似文献