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1.
13C and 15N spectroscopies at natural abundance have been applied to the study of nitrogen lone-pair delocalization in N? N containing compounds: nitrosamines, nitramines, hydrazines, hydrazones and triazenes. Structure-chemical shift correlations have been derived for nitrosamines; the 13C upfield effect of a γ substituent has been used for assigning the configuration of both diastereoisomers in N,N-unsymmetrically substituted nitrosamines. Equations have been computed which permit the prediction of the electronic delocalization, expressed in terms of free enthalpy of activation ΔG, as a function of δ15N and of the length of the N? N bond. 15N spectroscopy has also been applied to the study of the protonated species of nitrosamines and of acceptor-donor complexes of nitrosamines with Lewis acids. The behaviour of such N? N containing compounds is compared to that of amides.  相似文献   

2.
15N chemical shifts were measured in a series of anilinium fluorosulfonate salts and compared with chemical shift data from a comparable series of 15N-enriched aniline derivatives. A smaller overall range of nitrogen chemical shifts was observed for the protonated aniline series compared with that for the unprotonated anilines and is attributed to the elimination of nitrogen lone pair delocalization in the former series. Further-more, it was found that the range of nitrogen chemical shifts in the protonated anilines is determined primarily by substituent electronic effects from the ortho ring position with almost negligible contributions from the para position.  相似文献   

3.
Several 15N enriched oximes of heterocyclic aldehydes have been prepared in syn and anti forms. The less stable form may be obtained by UV irradiation of the other one. The geminal 15N? H coupling in the R? CH?15N? OH fragment allows an immediate and unambiguous assignment of the configuration to be made, being 13 to 16 Hz and 2 to 3 Hz for the anti and syn forms, respectively. Whereas oximes 1 to 4 are preferentially in the anti form, the N-methylpyridinium aldoxime iodides (2-PAM, 3-PAM, 4-PAM) are found to be syn in the stable form and not anti as previously thought. This reassignment is of special interest, since 2-PAM ( 8 ), which is an excellent antidote against alkyl phosphate nerve poisoning, has been used to study the geometry of the acetylcholinesterase active site of the enzyme.  相似文献   

4.
Different calculations, among them those utilizing the finite perturbation theory with INDO wave functions, have been effected to calculate the value of the 3J(1H ? N? N? 1H ) coupling constant in hydrazides as a function of the dihedral angle. Experimental coupling constants have been compared with calculated ones in order to determine the conformation around the N? N bond. The first example of a 2J(1H ? N? 15N ) coupling is described.  相似文献   

5.
For a series of compounds with N? C or N? N bonds, the CNDO/S parameterized calculations for Qπ, the electronic charge density on the nitrogen atom, and π bond orders Pπ provide evidence for the simultaneous dependence of the 15N chemical shift on both of these parameters. The multilinear regressions obtained produce high values for the regression coefficients. The results throw some light on the nitrogen lone pair delocalization mechanism.  相似文献   

6.
The 1H, 13C and 31P n.m.r. spectra of eleven 2-R-2-thiono-1,3,2-dithiaphosphorinanes with various R groups attached to the phosphorus atom have been recorded and analysed. In the compounds where R=Cl, OMe or N, the molecule adopts a chair conformation with the R group axially oriented. When the molecule adopts a chair conformation with equatorially oriented R. In the case of the derivatives with R=phenyl, Me, N(Me)2 or NHt-Bu, a chair–chair conformational equilibrium was observed. The hindered rotation about the P? N bond was also examined in the derivative with   相似文献   

7.
3-Aminopropanol reacts with aryl(or aralkyl or alkyl)isothiocyanates R? N?C?S to yield the corresponding thio-ureas R? NH? CS? NH? (CH2)3OH which, refluxed with hydrochloric acid, are cyclized by elimination of water. The cyclization products are identical with the hydrothiazines resulting by elimination of sulfate or phosphate from the sulfuric or phosphoric monoesters of these thio-ureas. The resulting hydrothiazines are either 2-(R-imino)-tetrahydro-m-thiazines (I) or 2-(R-amino)-dihydro-Δ2-m-thiazines (II). Their structure has been established by comparison of their spectra with those of model compounds in one of which the C?N double bond is certainly endocyclic (2-methyl-dihydro-Δ2-m-thiazine), the other presenting an exocyclic C?N double bond (3-methyl-2-phenylimino-tetrahydro-m-thiazine). When R is an aryl group, the C?N double bond is exocyclic (structure I with >C?N? Ar), and one may presume that this structure is stabilized by resonance. When R is an aralkyl or an alkyl group, the C?N double bond is endocyclic (structure II). The nmr spectra were taken with three types of solvent: CDCl3 or CCl4; (CD3)2SO; CF3COOH. In CF3COOH solution the benzylic protons of the hydrothiazine with R = pF? C6H4CH2? couple with NH (J=5,5cps) which confirms the endocyclic position of the C?N double bond in this case.  相似文献   

8.
The 1H NMR spectra of several 1,3,2-dioxaphosphorinanes bearing an extracyclic P? N bond have been analysed. The 3J(POCH) couplings are strongly dependent upon the orientation of the bond around the phosphorus atom. Depending upon the nature of the bonds attached to the nitrogen atom, the dioxaphosphorinane ring may adopt either a fixed chair conformation with the P? N bond in the axial or equatorial orientation, or it may be in equilibrium between two chair conformations where the P? N bond is alternately axial or equatorial. The equilibrium is fast on the NMR time scale.  相似文献   

9.
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   

10.
13C NMR chemical shifts were measured in CDCl3 for two series of substituted benzylidene anilines. The substituted benzylidene anilines p-X-C6H4CH=NC6H4-p-CN p-X-C6H4CH=NC6H4-o-CN (X = NO2, F, Cl, Br, H, Me, MeO, NMe2). The substituent dependence of δC(C=N) was used as a tool to study electronic substituent effects on the azomethine unit. The benzylidene substituents X have a reverse effect on δC(C=N): electron-withdrawing substituents cause shielding, while electrondonating ones do the reverse, the resonance effects clearly predominating over the inductive effects. Additionally, the presence of a specific cross-interaction between X and C=N could be verified. The electronic effects of the neighboring aromatic ring substituents systematically modify the sensitivity of the C=N group to the electronic effects of the benzylidene substituents. These results can be rationalized in terms of the substituent-sensitive balance of the electron delocalization (mesomeric effects).  相似文献   

11.
The rearrangement in trifluoroacetic acid of two indole alkaloids of the echitamine series, desformocorymine (14) and dihydrocorymine (9) , has been investigated. Desformocorymine (14) was tranformed into a mixture of carbinolamines 17a , b , with the akuammiline skeleton, which were reduced (Et3SiH, CF3CO2H) into an isomer 12 of cathafoline (6). This sequence constitutes the first example of an interconversion of the corymine skeleton into the akuammiline skeleton (Scheme 2). In the case of dihydrocorymine (9) , the rearrangement followed a different pathway owing to the formation of a hemiacetal between the primary alcohol CH2(17)-OH and a carbonyl formed at C(3). Treatment of this hemiacetal 26 with aqueous base led to its opening with concomitant formation of a lactam. 13C-NMR seems to indicate that this lactam exists under a hydrated form 27. This highly unstable intermediate was cleanly transformed (MeONa-MeOH) into a 2-acyl indole 30 (Scheme 4), the structure of which was determined by X-ray crystallography. The formation of this acylindole involves the rupture of the C(7)? C(16) bond; it is the reverse of the reaction generally postulated as occurring in the biogenesis of the pentacyclic alkaloids. The structure of a by-product 34 was established as 17-hydroxymethylvincoridine by X-ray crystallography. The acid-catalyzed rearrangements involve the rupture of the Ph-N? C? N chromophore, with formation of a carbonyl at C(3). The reversibility of these steps is used in an easy correlation of dihydrocorymine and of 3-epidihydrocorymine via their trifluoroacetates.  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.
The pulse sequence INEPT was used to obtain proton-coupled 15N-NMR spectra in natural isotope abundance for enamines substituted in 2-position with electron-with-drawing groups. The chemical shifts and coupling constants are discussed in terms of their relationship to structural features such as multiple N-alkyl substitution, double-bond configuration, H-bonding, N-lone-pair delocalization within the conjugated system, and steric effects. It is concluded that 15N chemical shifts are a sensitive probe for local structural modifications at the N-atom and conformational changes in a remote part of a conjugated molecule, while one-bond N,H-coupling essentially reflects N-hybridization and subtle local geometric distortions. Stereospecific three-bond N,H spin coupling to olefinic protons (4.0 ± 0.2 Hz) has been found a characteristic feature of (Z)-isomers in all investigated compounds, whereas two-bond coupling to olefinic protons (2J(N,H) = 0.5 to 5 Hz) is observed in (E)-isomers. The sensitivity to solvents and steric properties of remote substituents renders geminal coupling a useful probe for studying electronic effects in the C? N bond.  相似文献   

14.
14N-NMR. measurements using the Fourier Transform technique are presented and compared to C. W. experiments. The F. T. technique is especially advantageous for relaxation time measurements. However, since 14N-nuclei may have widely different relaxation times, it is often not possible to have optimal gain in sensitivity (as compared to C. W. measurements) in a single F. T. experiment for different 14N-nuclei contained in the same sample. Different experiments have to be performed, optimizing the spectrometer parameters for each 14N-resonance of appreciably different linewidth. The technique is applied to three different problems. 14N-relaxation in symmetrical ammonium salts is shown to arise from reorientation of the water dipoles. The use of a double spin-probe, 13C-14N, allows the determination of the electric field gradients in cyclic ammonium salts. The electronic distribution is especially distorted from tetrahedral symmetry in the highly strained N, N-dimethyl-aziridinium cation. Finally, electric and dynamic effects in ion pairing may be studied as shown on the case of tetrabutylammonium iodide in water and in benzene.  相似文献   

15.
The ΔG* values for the barrier to rotation around the P? N bond have been determined in some aminophosphines and are dependent on the substituents bound to the phosphorus atom. The comparison between 3J(P? N? C? H) and ΔG* values indicates that pπdπ overlapping between nitrogen and phosphorus is the main effect. The nucleophilic behaviour of the nitrogen atom has been measured by the rate of the chemical exchange between methyl-trifluoroacetate and various aminophosphines: the results of this kinetic study are in good agreement with the NMR conclusions.  相似文献   

16.
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   

17.
1H and 13C NMR spectra of 15N-methylaniline, 15N-methylphenylpropargylamine and 15N-methylphenylpropynylamine have been studied. The s character of nitrogen, deduced from 1J(15N? 13C) and 1J(15N? 13C), indicates that nitrogen hybridisation is intermediate between sp3 and sp2 in 15N-methylaniline and 15N-methylphenylpropargylamine, while nitrogen is sp2 in the α-acetylenic amine. The 1J(15N? 13Csp)cou pling constant calculated with the help of Binsch's relation does not agree with the experimental value, suggesting that orbital and dipolar mechanisms make substantial contributions to this coupling constant.  相似文献   

18.
Dipolar relaxation of 15N in anilines and anilinium ions is influenced by overall motion of the molecule, by rotation about the aryl–-nitrogen bond, by inversion of the aniline nitrogen and by interactions of the NH2 or NH3+ group with the solvent. These factors are assessed by comparison of the 13C and 15N dipolar relaxation times as a function of para-substitution on the aryl ring. In the anilines (solvent CDCl3), electron withdrawal brings about faster relative motion of the amine side-chain, contrary to expectation from consideration of C? N rotation but in agreement with the effects from nitrogen inversion. The 15N dipolar relaxation time correlates with the Hammett σp. For the anilinium ions (solvent Me2SO-d6), there is no correlation with σp and no qualitative relationship with either C? N rotation or N inversion. Nitrogen-15 relaxation, corrected for overall motion as judged by ring 13C relaxation, correlates with the inductive parameter σI. Electron withdrawal through induction reduces hydrogen bonding and increases side-chain mobility. For most of the anilines and for all of the anilinium ions, solvent interactions cause the nitrogen side-chain to be less mobile than the aryl ring. Under these circumstances, the Woessner approach cannot be used to calculate barriers. The hydrogen bond donor properties of the anilines are reduced in the absence of electron-donating substituents, and the first barriers to NH2 rotation/inversion were calculated by this procedure: aniline in CDCl3 3.5 kcal/mol, p-chloroaniline in CDCl3 3.4 kcal/mol and p-nitroaniline in acetone 3.8 kcal/mol.  相似文献   

19.
The synthesis of crystalline 1-(2-pyrimidyl)-4-(3, 4-methylenedioxybenzyl)-piperazin methanesulfonate (ET 495) labelled with 14C fixed on the piperazine nitrogen N(4) has been realized in five steps from barium carbonate 14C; Specific activity of the final product: 32,8 mCi/mmol (110 m?Ci/mg); radiochemical purity: around 99%. The mass spectrum of the labelled compound is in agreement with the chemical structure and the labelling position expected.  相似文献   

20.
In order to find support for the validity of the hypothesis proposed by one of us regarding the different natures of the bonds in the four successive complexes formed between Ag+ and thiourea, the corresponding enthalpies are verified by direct calorimetry.Furthermore, because the influence of substituent groups on the nitrogen atoms may help to characterize the donor atom. the calorimetric enthalpies and potentiometric free energies of complexation between Ag+ and N-methylthiourea, N,N′- dimethylthiourea and N,N′-diethylthiourea have also been determined at 25°C, in aqueous medium of ionic strength μ = 0.5 M KNO3.  相似文献   

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