Etude par RMN du Proton et du Carbone-13 de Pyrimidines Substituées. I—Effets de Substituant dans les Dérivés Méthylés et Aminés

Substituent effects of methyl and amino groups on the chemical shifts of pyrimidine have been investigated by ¹H and ¹³C n.m.r. and compared with similar data obtained for benzene and pyridine. Taking into account pairwise interactions, the chemical shifts calculated by using an additivity relationship are in very good agreement with the experimental results, except for some hindered pyrimidines. This study enabled us to assign the ¹³C n.m.r. spectra of some trisubstituted pyrimidines.     

RMN 13C de cyclanones halogénées. Détermination et additivité des incréments du chlore en série cyclohexanique

The ¹³C n.m.r. spectra of fourteen chlorocyclohexanones have been recorded to examine the variation of the ¹³C chemical shifts as a function of the position and the number of the chlorine substituents. Additivity relationships were found which enable reasonable prediction of the chemical shifts of chlorinated cyclohexanones. Comparison between the observed and calculated chemical shifts of mono- and dichlorinated flexible molecules shows that the chlorine effects are additive.     

Synthèses stéréospécifiques et étude organoleptique comparée de onze triméthyl-2,2,3-exo-norbornyl-5-exo-cyclohexanols racémiques

The stereospecific syntheses of the eleven racemic 2,2, exo-3-trimethyl-exo-5-norbornyl-cyclohexanols related to the formula VI have been achieved. Moreover, the fragrant properties of these isomeric and stereomeric cyclohexanols have been carefully estimated by a team of four well-experienced perfumers. In good agreement with our earlier observations [1 ab], it was concluded that the axial 3-(2,2, exo-3-trimethyl-exo-5-norbornyl)-cyclohexanols, threo (XXIV) and erythro (XXIX), are the only isomers which display a very powerful and genuine sandalwood odour. The other cyclohexanols were found to be about 20–100 times less fragrant (4 compounds), or practically odourless (5 compounds).     

Etudes des sélénophènes mono et bisubstitués par Résonance Magnétique de 1H et de 13C

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 ¹³C? ⁷⁷Se are shown to be good structural parameters and a set of substituent additivity constants is calculated.     

Etude en Résonance Magnétique Nucléaire du Carbone-13 de N-Aryl Pyrazolines-2 Diversement Substituées. Effets de Substituant et Etude Conformationnelle

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.     

Applications de la Résonance Dynamique du Proton et du Carbone-13 à l'Etude d'Azines Hétérocycliques. Mécanismes de Formation et d'Isomérisation

A ¹H and ¹³C n.m.r. study of heterocyclic azines is presented and the influence of Z/E isomerism on the ¹³C chemical shifts is examined. The kinetic study of the formation and Z/E isomerization of these compounds has been carried out and mechanisms of these reactions are discussed.     

Structure and stability of closo-BnHn−2(CO)2 (n = 5–12)

Closo-B_nH_n−2(CO)₂ (n = 5–12), isolobal analogues of closo-C₂B_n−2H_n, have been investigated at the B3LYP/6-311+G^**density functional level of theory. The most stable isomers of closo-B_nH_n−2(CO)₂ are similar to those of closo-C₂B_n−2H_n in geometric patterns apart from closo-B₆H₄(CO)₂, and closo-B_nH_n−2(CO)₂ is much less strained than closo-C₂B_n−2H_n. Energetic analysis identifies closo-B₆H₄(CO)₂, closo-B₁₂H₁₀(CO)₂ and closo-B₁₀H₈(CO)₂ to be most stable, of which the latter two cages have been prepared experimentally. On the basis of the negative and rather large nucleus independent chemical shifts (NICS), closo-B_nH_n−2(CO)₂ are aromatic. To aid further experimental study, the CO stretching frequencies have been computed.     

Structure moléculaire et propriétés moléculaires de quatre isomères de formule C8H10N4

The molecular structures of the three Meyer isomers [3-methyl-3-(5′-amino-3′-methyl-l-pyrazolyl)acrylonitrile; acetylacetonitrile azine; 2,5-dimethyl-7-aminopyrazolo[1,5-a]pyrimidine] have been compared with that of the fourth isomer, 2,7-dimethyl-5-amino-pyrazolo[1,5-a]pyrimidine. The CNDO/2 and CNDO/S calculations utilizing these geometries have been accomplished. These include electronic transitions, dipole moments, ionisation potentials, charge densities, bond ordres and total energies. The calculated values have been compared to some experimental data. Uv spectra, ¹³C chemical shifts, ¹H-¹H coupling constants and relative stability of the four isomers are included.     

Etude en Résonance Magnétique Nucléaire du Carbone-13 de Quelques Aminopyrazoles. Sur le Problème de la Détermination des Constantes d'Equilibre Tautomère

The ¹³C chemical shifts of 32 pyrazoles were measured in hexadeuterated dimethyl sulphoxide and in hexamethylphosphorotriamide. Substituent effects (methyl and amino groups on the pyrazolic carbons, and methyl, n-butyl and phenyl groups on the nitrogen) were calculated by multilinear regression analysis. The general problem of the ¹³C NMR study of annular tautomerism in azoles is discussed and illustrated by the 3(5)-aminopyrazole case.     

Séparation et dosage automatisés des acides phénoliques végétaux par chromatographie sur colonne de polyclar et spectrophotométrie dans l''ultra violet

Quantitative autoanalysis of phenolic acids by liquid chromatography on a Polyclar column and ultraviolet spectrophotometry

Phenolic acids of wide occurrence in plants have been separated by liquid chromatography on a Polyclar column. Experimental conditions leading to an optimal resolution have been defined (eluting solvents, elution gradient, flow rate, column length, and elution temperature). Each compound eluted from the adsorbant was automatically estimated quantitatively by a recording ultraviolet spectrophotometer: quantities as low as 0.1 μmole could be detected.

The application of this method to the study of phenolic acids in plants and also to the separation of other phenolic compounds is discussed.     

Spectroscopie RMN du Carbone-13 de Thiocétones Aliphatiques: Propanethione et Dérivés,Thiocétones Bicycliques et α Cyclopropaniques

Carbon-13 NMR spectra of various aliphatic ketones and thioketones were determined and interpreted. As shown by the relation between ¹³C chemical shifts in C=A groups, the C=S is more sensitive to the substituents than the C=O group. Conjugative effects are more pronounced in α-cyclopropyl thioketones than in α-cyclopropyl ketones.     

Etude par Résonance Magnétique Nucléaire du carbone 13 de complexes du cobalt (III) et de la diméthylglyoxime

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.     

Spectres de rotation de la molécule de chlorobenzéne : I. Variétés isotopiques monosubstituées et structure rs

The microwave spectra of chlorobenzene “(1)-³⁵Cl”, all eight mono-[“(1)-³⁷Cl”, “(1)-³⁵Cl, (2)D”, “(1)-³⁵Cl, (3)D”, “(1)-³⁵Cl, (4)D”, “(1)-³⁵Cl, (1)-¹³C”, “(1)-³⁵Cl, (2)-¹³C”, “(1)-³⁵Cl, (3)-¹³C”, “(1)-³⁵Cl, (4)-¹³C”], one di[“(1)-³⁵Cl, (2,6)D₂,”] and one trisubstituted species [“(1)-³⁷Cl, (2,6)D₂”] have been investigated. From the moments of inertia of the vibrational ground state the r_s structure was derived. The reliability of the two small a coordinates could be enhanced through use of the multiply substituted species. The errors of the moments of inertia were propagated to the structural parameters. It could be shown that the benzene ring is deformed. However the quantitative deformation could not be established due to the rather large errors of some structural parameters.     

Recherches sur la stéréochimie des diènes fonctionnnels—XI: Interprétation théorique des déplacements chimiques de stéréoisomères D'éthoxybutadiènes-1,3

A theoretical analysis of the proton chemical shifts of alkoxy-1,3-diene stereoisomers is proposed. The diamagnetic contribution is calculated from π and σ theoretical indices obtained by the CNDO/2 method. This effect depends on the stereochemistry of the molecule and the charges and chemical shifts alternate in the same way. The diamagnetic part is often small compared to the experimental value, however, and the paramagnetic contribution Δδ_p is important. Δδ_p is difficult to explain with the usual models of anisotropic and electric contributions, but the results give useful information on the conformations of the molecules.     

Etude par Résonance Magnétique Nucléaire de dérivés anthracéniques: II—Anisotropie magnétique du phényle et effets steriques

The peri effect induced by the phenyl group has been studied in the anthracene series by means of ¹H and ¹³C n.m.r. The chemical shifts of overcrowded protons can be explained by a combination of magnetic anisotropy and steric effects. Steric contributions amount to c. 25% of the phenyl induced shift at the peri position. Amongst published ring-current theories, only the model of Johnson and Bovey is capable of describing correctly the shielding region of the phenyl group. The unexpected shieldings and deshieldings, observed by ¹³C n.m.r. in the case of very hindered derivatives, is probably due to distortions of the anthracene skeleton.     

Conformation et Spectrometrie de RMN. III. Spectres 13C de Diméthylamino Cyclanols et Dérivés

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.     

Étude en RMN du 13C de Dérivés de la Pipéridone-4 Stériquement Encombrés et des Oximes Correspondantes

The regiospecific differences in chemical shifts caused by the oximino group, such as Δδ as Δδ parameters, are useful to estimate conformational distortions directly from ¹³C spectra. Particularly, twist-boat conformations resulting from oximation of sterically hindered piperidones are unambiguously detected.     

Theoretical study on the structure and stability of hydrogen-ion clusters Hn and Hn (n = 3, 5, 7, 9, 11, 13)

Ab initio SCF and CI calculations have been carried out for H_n⁺ and H_n⁻ (n = 3, 5, 7, 9, 11, 13) clusters with a double-zeta plus polarization basis set. The stabilization energy of negative ion clusters H_n⁻ is very small (less than 1 kcal) and their existence is critical. The structural difference between positive- and negative-ion clusters are discussed in terms of the bonding ability involved. While H_n⁺ is a charge-transfer complex, the stability of H_n⁻ comes mainly from the ion-induced-dipole attractions. The electron correlation effect on the structure and stability of these ion clusters is also discussed.     

Résonance magnétique nucléaire de 13C et 17O d'éthers aliphatiques. Effets γ entre les atomes d'oxygène et de carbone

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 δ_c for carbon atoms can also be correlated with δ_c 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.     

Déplacements Chimiques du Carbone 13, Constantes de Couplage 1J(CH) et 3J(CH) dans une série de dérivés trisubstitués du benzène

¹³C chemical shifts, 1-bond and 3-bond (meta) ¹³C? H coupling constants have been determined in a series of trisubstituted benzene; the substituents are Cl, NH₂, N(C₂H₅)₂, N(iC₃H₇)₂, N(C₂H₄)₂O. Chemical shifts are only in moderate agreement with the usual additivity rules. Additivity rules relative to the above mentioned coupling constants are proposed. With few exceptions, the difference between predicted and observed values is less than 10%.