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Showing papers in "Magnetic Resonance in Chemistry in 1974"


Journal ArticleDOI
TL;DR: In this article, the carbon-13 NMR spectra of tetra-and pentacyclic triterpenoid spectra have been obtained for methyl, methylene, methine and quaternary carbon atoms.
Abstract: The carbon-13 NMR spectra of lanosta-8-en-3β-ol, lanosta-8, 24-dien-3β-ol, lanosta-7,9(11)-dien-3β-ol, lanostan-3β-ol, eupha-8-en-3β-ol, eupha-8,24-dien-3β-ol, ursa-12-en-3β-ol (α-amyrin) and oleana-12-en-3β-ol (β-amyrin) have been obtained and completely assigned. The results of this study provide chemical shift data for methyl, methylene, methine and quaternary carbon atoms in tetra- and pentacyclic triterpenoid spectra. The carbon-13 NMR spectrum of a triterpenoid provides a unique fingerprint for the molecule.

110 citations


Journal ArticleDOI
TL;DR: In this paper, the inductive and mesomeric substituent effects on the polarisation and charge density of the CNC bonds were discussed in terms of the inductively and mesomally substituents.
Abstract: 13C chemical shifts and 1J(14N13C) coupling constants as well as stretching frequencies of the isocyano group are reported for some representative aliphatic, unsaturated and aromatic isocyanides and for two copper(I) isocyanide complexes. The results are discussed in terms of the inductive and mesomeric substituent effects on the polarisation and charge density of the CNC bonds. The marked solvent effect on the chemical shifts of the isocyano carbon hampers comparison of our data with previously reported data. The hydrogen bonding shift of this carbon in water or methanol is much smaller than previous data suggest.

95 citations


Journal ArticleDOI
TL;DR: In this article, 13C chemical shifts are reported for adamantane, nine 1-substituted adamantanes and nine 2-substantified adamantanes, and substituents are F, Cl, Br, I, NH2, OH, CH2, CN and CO2H.
Abstract: 13C chemical shifts are reported for adamantane, nine 1-substituted adamantanes and nine 2-substituted adamantanes. The substituents are F, Cl, Br, I, NH2, OH, CH2, CN and CO2H. The assignments and results are discussed in terms of chemical shift patterns.

55 citations


Journal ArticleDOI
TL;DR: In this paper, a correlation has been found for the carbonyl and thiocarbonyl resonances which has been discussed as being mainly influenced by the mean excitation energy in the paramagnetic screening term.
Abstract: Die 13C-chemischen Verschiebungen von methylsubstituierten Harnstoffen, Thioharnstoffen und verwandten Verbindungen werden diskutiert Es wurde eine Korrelation von 13CO und 13CS-chemischen Verschiebungen gefunden Die mittlere Anregungsenergie im paramagnetischen Verschiebungsanteil wird fur die Anderung der Verschiebungen bei Ubergang von Carbonyl- zu entsprechenden Thiocarbonyl-Verbindungen als wesentlich angesehen Einfache HMO-Berechnungen der Ladungsdichte konnen die Trends der 13C-chemischen Verschiebungen nicht wiedergeben The 13C-chemical shifts of methyl substituted ureas, thioureas and related compounds are reported and discussed π-Electron densities, as obtained by simple HMO calculations, do not reproduce the 13C-chemical shift trend A correlation has been found for the carbonyl and thiocarbonyl resonances which has been discussed as being mainly influenced by the mean excitation energy in the paramagnetic screening term

54 citations


Journal ArticleDOI
TL;DR: In this paper, a 300 MHz spectral study of mono-to trisubstituted cyclohexanes was conducted, allowing a re-examination of some of their 1H NMR spectral parameters.
Abstract: From a 300 MHz spectral study of mono-to trisubstituted cyclohexanes, allowing a re-examination of some of their 1H NMR spectral parameters, it is shown that it is possible to predict with reasonable accuracy the shifts (in CCl4) of the ring protons. A substantial feature in this is the validity of the (questioned) additivity of multiple effects. It is also shown that with respect to shift alterations, equatorial ring protons behave anomalously, which cannot be explained by any existing theoretical model.

52 citations


Journal ArticleDOI
TL;DR: In this paper, the application of selective population inversion (SPI) to the assignment of 13C resonances and to the determination of the relative sign of the 13C1H coupling constants is demonstrated for 1-phenyl-1,2-dibromo-2-nitroethane.
Abstract: The application of selective population inversion (SPI) to the assignment of 13C resonances and to the determination of the relative sign of 13C1H coupling constants is demonstrated for 1-phenyl-1,2-dibromo-2-nitroethane. A negative sign for the geminal C-2H-1 coupling constant has been determined from the 13C spectra. The relationship between SPI and TSI is discussed.

51 citations


Journal ArticleDOI
TL;DR: In this article, a linear relationship exists between carbon-13 chemical shifts and the calculated electron densities, and also between substituent constants and electron density, and a slope of 4/3 is obtained between the direct coupling constant 1J(CH) of α carbon in monosubstituted ethylenes and that in the corresponding substituted methanes.
Abstract: Carbon-13 chemical shifts of sixteen monosubstituted ethylenes were obtained. In order to explain the chemical shifts, σ and π electron densities of these compounds are calculated by the σ-included ω-HMO method.1 A linear relationship exists between carbon-13 chemical shifts and the calculated electron densities, and also between substituent constants and electron densities. A slope of unity is obtained between the chemical shifts of α carbons of monosubstituted ethylenes and those of carbons adjacent to the substituents in monosubstituted benzenes. On the other hand, a plot of chemical shifts of Cortho of benzene derivatives against that of the β carbon in ethylene derivatives gives a slope of 3. These slopes can be explained by the calculated electron densities. A slope of 4/3 is obtained between the direct coupling constant 1J(CH) of the α carbon in monosubstituted ethylenes and that in the corresponding substituted methanes.

45 citations


Journal ArticleDOI
TL;DR: In this paper, the carbon-13 chemical shifts of three arylmethyl carbanions were determined by changing solvents and counter ions and compared with those obtained from the 1H chemical shifts.
Abstract: Carbon-13 chemical shifts of three arylmethyl carbanions have been determined by changing solvents and counter ions. The charge distributions in the carbanions are discussed and compared with those obtained from the 1H chemical shifts.

42 citations


Journal ArticleDOI
TL;DR: In this article, the deuterium atom was added to the carbon-13 spectra of 1-methylnaphthalene, 1-fluoronaphthalenes, l-naphthonitrile and their 4-deutero analogues.
Abstract: The natural abundance, proton-decoupled carbon-13 spectra of 1-methylnaphthalene, 1-fluoronaphthalene, l-naphthonitrile and their 4-deutero analogues, as well as 2-naphthol and its 6-deutero analogue, have been recorded. Careful comparisons of the spectra of the deuterated and undeuterated compounds allow assignment, not only of the deuterated carbon, but also of the two ortho carbons (based on an upfield ‘two-bond’ deuterium isotope effect), as well as the two meta carbons (based on a significant J(CCCD) of ∼1 Hz) which causes substantial broadening). In the 1-naphthyl compounds, significant coupling between the deuterium (at C4) and C5 allows assignment of this latter carbon. Thus, the consequences of the introduction of one deuterium atom, together with results from off-resonance noise decoupling, permits assignment of most of the spectra. Tentative, but very likely assignments of the few remaining signals, can be made on the bases of chemical shifts and compressional effects. This approach could allow indirect assignment of an aryl carbon to which direct attachment of deuterium is difficult, due to directive effects of an existing substituent.

41 citations


Journal ArticleDOI
A. J. de Hoog1
TL;DR: In this article, the effects of substituents on α, β, γ and δ-carbon atoms were discussed and the γ-parameter can be used for quantitative conformational analysis.
Abstract: Fourier transform carbon-13 nuclear magnetic resonance spectra have been obtained and interpreted for some 2-substituted tetrahydropyrans. The effects of the substituents on α, β, γ and δ-carbon atoms are discussed. Using suitable reference compounds the γ-parameter can be used for quantitative conformational analysis.

31 citations


Journal ArticleDOI
TL;DR: The preferred solute conformation of ethyl 3α-phenyltropane-3β-carboxylate hydrochloride, the tropane analogue of pethidine, is shown to be a piperidine chair with an axial 3-phenyl substituent by analysis of its 1H NMR characteristics and spectral comparisons with model compounds as mentioned in this paper.
Abstract: The preferred solute conformation of ethyl 3α-phenyltropane-3β-carboxylate hydrochloride, the tropane analogue of pethidine, is shown to be a piperidine chair with an axial 3-phenyl substituent by analysis of its 1H NMR characteristics and spectral comparisons with model compounds. Conformational studies of synthetic intermediates are also reported and favoured boat forms identified for 3α-diphenylhydroxymethyl-3β-tropanol and 3α-phenyl-3β-tropanyl phenyl ketone. In the hot-plate test for analgesia performed on mice, ethyl 3α-phenyltropane-3β-carboxylate is about 1·5 times as effective as pethidine.

Journal ArticleDOI
TL;DR: Carbon-13 chemical shifts have been obtained in the pulse Fourier transform mode on the following cholinergic neural transmission agents and the observed chemical shifts do not appear to correlate simply with potencies in the Cholinergic nervous system.
Abstract: Carbon-13 chemical shifts have been obtained in the pulse Fourier transform mode on the following cholinergic neural transmission agents: acetylcholine, β-methyl acetylcholine, carbamoyl choline, choline, tetramethylammonium, scopolamine, atropine, methyl atropine, tropine, tropic acid, nicotine, dimethyl phenylpiperazinium, arecoline, oxotremorine and pilocarpine. The effects of structural variations, asymmetric centers and steric interactions on the 13C shielding are considered. The observed chemical shifts do not appear to correlate simply with potencies in the cholinergic nervous system.

Journal ArticleDOI
TL;DR: In this article, the s-cis and s-trans rotamers of enamino ketones and thiones of the general formula (where × = O or S and R-1, R-4 = alkyl) were obtained with dimethylaminoacrolein and its thione analogue.
Abstract: Carbon-13 magnetic resonance spectra of the s-cis and s-trans rotamers of enamino ketones and thiones of the general formula (where × = O or S and R-1, R-4 = alkyl) have been obtained With dimethylaminoacrolein and its thione analogue, restricted rotation could only be observed in the latter The chemical shift differences between rotamers and homologues are attributed to changes in conjugation and to induced bond polarisation, both these factors resulting from steric strain In particular, nonplanar deformations of the s-trans rotamers are deduced from their C-2 chemical shift values

Journal ArticleDOI
TL;DR: In this paper, the Karplus equations and their modifications (with and without corrections for the electronegativity of adjacent groups) were found to provide satisfactory correlations between these parameters, and the optimum coefficients for the equations connecting the spin-spin coupling constants (J) of the vicinal protons and the dihedral bond angles (DBA) determined from an X-ray study in the HCCH bond system.
Abstract: Conformationally rigid systems such as xylopyranose 1,2,4-ortho esters (1a) and (1b) and 10-methoxy-6-aza-isoadamantane (2), for which the identity of conformations both in the crystalline state and in solution can reasonably be assumed, provide good models for the study of experimental correlations between the spin–spin coupling constants (J) of the vicinal protons and the dihedral bond angles (DBA) determined from an X-ray study in the HCCH bond system. The Karplus equations and their modifications (with and without corrections for the electronegativity of adjacent groups) were found to be unable to provide satisfactory correlations between these parameters. Optimum coefficients for the equations connecting the J and DBA values with corrections for electronegativity were calculated by the least squares method. The same procedure was used to obtain an equation connecting the J with DBA values using the sum of the chemical shifts as a measure of the electronic factors affecting the J ∝ DBA dependence. The accuracy of the equation thus obtained lies within ±18% as opposed to ±48% for the original Karplus equations. A similar correlation was obtained for the angles between the intercrossing lines formed by the directions of the vicinal CH bonds (ILA). When combined with the sum of chemical shifts, ILA provides a better correlation with the coupling constants J than the conventional parameter DBA.

Journal ArticleDOI
TL;DR: An NMR method is described for assaying the enantiomer composition of the pharmacologically active material penicillamine, using tris-(3-heptafluorobutyryl-d-camphorato)europium, which can be detected at levels of 0·4 to 0·5% in DL mixtures.
Abstract: An NMR method is described for assaying the enantiomer composition of the pharmacologically active material penicillamine (1), using tris-(3-heptafluorobutyryl-d-camphorato)europium. The L enantiomer can be detected at levels of 0·4 to 0·5% in DL mixtures. Problems due to the insolubility of penicillamine in nonpolar solvents can be overcome by a two step derivatisation procedure.

Journal ArticleDOI
TL;DR: In this article, the 1H NMR spectra of photodimers of cinnamic acid, chalcone and related compounds were analyzed, and the spectral parameters and all the coupling constants were obtained.
Abstract: 1H NMR spectra of photodimers of cinnamic acid, chalcone and related compounds were analysed, and the spectral parameters and all the coupling constants were obtained A clear differentiation among the head-to-head and head-to-tail stereoisomers can be obtained by considering the values of K, L, M and N parameters The different types of hh and ht isomers can be immediately assigned by considering the relative values of the three-bond couplings An authentic example of an A2B2 spin system is reported

Journal ArticleDOI
TL;DR: In this paper, a method for the calculation of gauche coupling constants from substituent electronegativities by taking into account the orientation of the substituents is described.
Abstract: The calculation of gauche coupling constants from substituent electronegativities by a method which takes into account the orientation of the substituents is described. This correlation has been derived from the coupling constants of disubstituted ethanes and has been applied to the calculation of coupling constants in cyclohexanes and 6-membered heterocycles. The detection of angular distortion in 6-membered rings from the difference between calculated and observed coupling constants is also described.

Journal ArticleDOI
TL;DR: In this article, carbon-13 NMR chemical shifts and one-bond carbon-hydrogen coupling constants have been obtained at 15·09 MHz for tautomeric hydroxypyrazine and compared with the 13C NMR spectra of 2-, 3- and 4-hydroxypyridines.
Abstract: Carbon-13 NMR chemical shifts and one-bond carbon–hydrogen coupling constants have been obtained at 15·09 MHz. The trends in the carbon chemical shifts obtained for the pyrazines parallel those of monosubstituted benzenes and 2-substituted pyridines, except for the direct effect of substitution where the pyrazines resemble pyridines not benzenes. The substituent effects on the 13C NMR spectra are generally quite similar to those in the 1H NMR spectra. The 13C NMR spectrum of the tautomeric hydroxypyrazine has been compared with the 13C NMR spectra of 2-, 3- and 4-hydroxypyridines. Hydroxy compounds that can exist as a cyclic amide show a large meta substituent effect on the chemical carbon shift.

Journal ArticleDOI
TL;DR: In this paper, a plot of the 13C NMR chemical shift of a given carbon in a substituted propane versus that of the corresponding carbon in substituted butane showed a good linearity with a slope of unity.
Abstract: Carbon-13 NMR chemical shifts of several series of aliphatic hydrocarbon derivatives–-substituted methanes, ethanes, isopropanes, n-propanes and n-butanes–-were found to have a linear relationship with σ-electron densities (Qσ) calculated by the method of σ-included ω-HMO. A plot of the 13C NMR chemical shift of a given carbon in a substituted propane versus that of the corresponding carbon in a substituted butane showed a good linearity with a slope of unity. The values of the 13C chemical shifts of the n-butyl derivatives converged rapidly to a constant value as the distance from the substituent increased. Accordingly, the value for the δ-carbon was found to be constant regardless of the substituent. These results show that the 13C NMR chemical shifts of aliphatic hydrocarbon derivatives are mainly dependent on inductive effects. The convergence shown by the experimental results is supported by the calculated results of the Qσ values of the n-butyl derivatives.

Journal ArticleDOI
TL;DR: In this article, Heyden et al. describe the influence of l'orientation endo ou exo de l'heterocycle sur le glissement chimique du 13C pontal.
Abstract: L'etude RMN 13C de composes epoxybicyclo[2.2.1]‐heptaniques fait ressortir une forte influence de l'orientation endo ou exo de l'heterocycle sur le glissement chimique du 13C pontal. La difference entre les variations de glissements chimiques en 13C et 1H montre que l'effet de courant de cycle ne peut seul rendre compte des resultats observes. Copyright © 1974 Heyden & Son Ltd.

Journal ArticleDOI
TL;DR: In this article, the proton and carbon NMR spectra for a series of substituted indenes [C9H7R, R = H, CH3, Si(CH3)3] are reported.
Abstract: The proton and carbon NMR spectra for a series of substituted indenes [C9H7R, R = H, CH3, Si(CH3)3] are reported. The proton and carbon resonances for the 5-membered ring exhibit pronounced changes as a function of the substituents.

Journal ArticleDOI
TL;DR: In this paper, a relatively fast rotation around the α,β carbon-carbon double bond at the equilibrium of geometrical isomers and a comparatively slow rotation around a carbon-nitrogen single bond in compounds of the type ==================★★★★★★★★★★
Abstract: A relatively fast rotation around the α,β carbon–carbon double bond at the equilibrium of geometrical isomers and a comparatively slow rotation around the carbon-nitrogen single bond in compounds of the type (X1, X2 are electron-attracting substituents) were detected and investigated by the NMR technique. The relationships between the free energies of activation for these rotational processes and the character of the substituents, the number of double bonds, solvents and concentration were studied.

Journal ArticleDOI
TL;DR: In this paper, data on 13C chemical shifts and 13C1H spin coupling constants of norbornane (1), norbornene (2) and norbornadiene (3), benzonorbornen (4), and benzonorsorbornadienes (6) are reported.
Abstract: Data on 13C chemical shifts and 13C1H spin coupling constants of norbornane (1), norbornene (2), norbornadiene (3), benzonorbornene (4) and benzonorbornadiene (6) are reported. The non-equivalence in J(13CH) values determined from the two bridge methylene proton signals in 2,2,3,3-tetradeuteriobenzonorbornene (5) and 6 is briefly discussed. The extraordinary deshielding of the bridge methylene carbon in 6 has been noted.

Journal ArticleDOI
TL;DR: In this article, the chemical shifts of the aldehydic proton in furfural, thiophenealdehyde and benzaldehyde have been measured in fourteen solvents, and the correlation of chemical shifts was shown to correlate with benzaldehyde, (r = 0·992; 0·993).
Abstract: The chemical shifts of the aldehydic proton in furfural, thiophenealdehyde and benzaldehyde have been measured in fourteen solvents. The correlation of the chemical shifts of thiophenealdehyde and benzaldehyde is excellent (r = 0·996) while it is lower for furfural–benzaldehyde (r = 0·956). The long range coupling constant Jα5 of furiurai has been measured in twelve solvents and the rotameric mole fractions determined. The chemical shifts of individual rotamers are calculated and shown to correlate with benzaldehyde, (r = 0·992; 0·993). Only one rotamer is predominant for thiophenaldehyde in all solvents. The intrinsic solvent effects of the three aldehydes are similar.

Journal ArticleDOI
TL;DR: In this article, the relationship between the magnetic resonance spectra of mono-and disubstituted selenophenes and a set of substituent additivity constants is investigated.
Abstract: Une serie de selenophenes mono- et bisubstitues est etudiee en resonance de 1H et 13C. Les deplacements chimiques protoniques sont analyses en termes d'effets d'anisotropie et de champ electrique des substituants et utilises a une discussion des equilibres conformationnels. Les relations entre δ1H et δ13C et les charges π calculees par la methode PPP sont examinees. Les couplages 1J(13CH), nJ(13C ∼ H) et 1J(13C77Se) se revelent de bonnes caracteristiques structurales et des relations d'additivite sont degagees pour δ13C. Proton and carbon magnetic resonance spectra of mono-and disubstituted selenophenes are investigated. The proton chemical shifts are discussed in terms of magnetic anisotropy and electric field effects of the substituents, with a view to studying the conformational equilibrium of the carbonyl group. π Electronic charges, computed by the PPP method, are correlated with the proton and carbon chemical shifts. The coupling constants between 13C and 1H (1, 2 or 3 bonds) and 13C77Se are shown to be good structural parameters and a set of substituent additivity constants is calculated.

Journal ArticleDOI
TL;DR: The 19F and 31P NMR spectral parameters of a series of meta and para substituted phenylphosphonic difluorides were found to be linearly related to the substituent parameters.
Abstract: The 19F and 31P NMR spectral parameters of a series of meta and para substituted phenylphosphonic difluorides were found to be linearly related to the substituent parameters: the phosphorus chemical shifts correlated with Hammett's σ constant, the fluorine chemical shifts with Taft's σR parameter and the phosphorus–fluorine coupling constants with σ+.


Journal ArticleDOI
TL;DR: In this article, the 1H NMR spectra of several 1,3,2-dioxaphosphorinanes bearing an extracyclic PN bond have been analyzed.
Abstract: Le spectre de resonance magnetique nucleaire du proton de divers dioxaphosphorinanes-1,3,2, qui portent au niveau du phosphore une liaison PN extracyclique a ete analyse. Cette etude confirme que, pour une disposition geometrique donnee des atomes P, O, C et H, le couplage 3J(POCH) depend fortement de l'orientation des liaisons au niveau du phosphore. Suivant la nature des restes attaches a l'atome d'azote, le cycle dioxaphosphorinane adopte une forme du type chaise rigide a liaison PN axiale ou equatoriale, ou au contraire une forme chaise qui s'inverse rapidement pour le temps d'observation de la RMN. The 1H NMR spectra of several 1,3,2-dioxaphosphorinanes bearing an extracyclic PN 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 PN bond in the axial or equatorial orientation, or it may be in equilibrium between two chair conformations where the PN bond is alternately axial or equatorial. The equilibrium is fast on the NMR time scale.

Journal ArticleDOI
TL;DR: In this paper, Hartree-fock calculations at the INDO level have been performed on the radical anions of dibenzoselenophene and 2,1,3-benzoselenadiazole, the phenoselenazine radical cation and the phenoseslenazine neutral radical.
Abstract: MO calculations based on the finite perturbation theory in the INDO approximation have been carried out on selenophene, eighteen of its monosubstituted derivatives and benzo (b)selenophene. The calculated nuclear spin coupling constants satisfactorily reproduce signs, magnitudes, internal orders and some trends of the experimental values. Comparison of different ZDO calculations provides information on the relative importance of σ and π pathways for the various coupling constants in selenophene and benzo(b)selenophene. Unrestricted Hartree-Fock calculations at the INDO level have been performed on the radical anions of dibenzoselenophene and 2,1,3-benzoselenadiazole, the phenoselenazine radical cation, the phenoselenazine neutral radical and the phenoselenazine nitroxide. The isotropic hyperfine coupling constants have been found to be generally in satisfactory agreement with experiment.

Journal ArticleDOI
TL;DR: In this paper, the NMR spectra of a series of heterocyclic compounds analogous to anthracene have been investigated at 220 and 60 MHz and the chemical shift of the proton ortho to the heteroatom was shown to be linear with respect to the electron density on heteroatoms, but otherwise chemical shifts are independent of electron density.
Abstract: The NMR spectra of a series of heterocyclic compounds analogous to anthracene have been investigated at 220 and 60 MHz. Correlations have been made with molecular geometry and parameters calculated from semi-empirical MO theory. For planar molecules, the chemical shift of the proton ortho to the heteroatom is linear with respect to the electron density on the heteroatom, but otherwise chemical shifts are independent of electron density. Planarity of the molecules is also a factor in some of the coupling constants.