Interactions intramoleculaires: XXII—Constantes de couplage, équilibres conformationnels et interactions gauches avec un groupement t-butyle (molécules cyclohexéniques deutériées)

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.     

Interactions intramoléculaires: XXIII—Constantes de couplage et interactions gauches avec un groupement t-butyle (cyclohexanones disubstituées 3, 4)

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°.     

Interactions intramoléculaires—XIX: Constantes de couplage vicinales, équilibres conformationnels et interactions gauches (séries cyclohexanique et cyclohexénique)

NMR parameters are determined and identified for the four stereoisomers of 3,4-dimethyl methoxycarbonylcyclohexane (d₃-2,2,3,4,5,5), the two stereoisomers of 2-methyl methoxycarbonylcyclohexane (d₅-2,3,4,5,5) and 3-methyl 4-X cyclohexene (d₃-3,6,6) (X = COOCH₃, CH₂OH, CH₂Cl). For the axial COOCH₃ substituted cyclohexane, the vicinal coupling constants are in agreement with the ring deformation. Different conformational equilibria are estimated and discussed, especially in relation to the inequality of gauche interactions between two cis vicinal substituents.     

Interactions intramoléculaires. XXVI—Constantes de couplage et hétérogénéités conformationnelles dans une série de R-3 et R-5 cyano-4 cyclohexènes deutériés (R=méthyl ou t-butyl)

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).     

Interactions Intramolécularies—XVII Calcul des constantes de couplage en RMN du cyclohexane et de cyclohexanes substitués. Comparaison des méthodes de Pople et Santry et des perturbations finies

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.     

Structure electronique des complexes acide-base de Lewis. I. Structure electronique et conformation moléculaire des molécules F3P·BH3 et F2HP·BH3

The electronic structure and preferred conformations of F₃P·BH₃ and F₂HP·BH₃ are investigated in the framework of the CNDO /2 approximation. In complete agreement with microwave data, the staggered conformations are predicted to be the most stable ones. The barriers to internal rotation are in good agreement with experimental values (F₃P·BH₃: calc. = 3.03 kcal/mole, exp. = 3.24 ± 0.15 kcal/mole; F₂HP·BH₃: calc. = 3.63 kcal/mole, exp. = 4.05 ± 0.45 kcal/mole) and a bicentric energy partitioning shows that the variations of the total energy are completely reflected by the only variation of the interaction energy between phosphorus and H atoms bonded to boron. The analysis of the electron densities reveals the importance of the 3s(P) → 2p_x(B) transfer in the formation of the co-ordination. Finally, the computed dipole moment value and direction agree with corresponding experimental data.     

Théorie quantique des phénomènes de biréfringence electrique et magnétique des molécules

A general formalism is set up to apply the variation-perturbation method to the quantum theory of non-linear optical effects, in particular to the electric and magnetic birefringence (Kerr and Cotton-Mouton effects). The quantities describing these effects are obtained from the wave function Ψ of the ground state of the unperturbed molecule and the different vectors and tensors which are determined by a variation method. With this method an approximate computation of the Kerr and Cotton-Mouton constants of some simple molecules has been made.     

Etude de nitrophénylhydrazones α-carbonylées—I. RMN des molécules modèles acycliques

The study of the α-carbonyl nitrophenylhydrazones by NMR requires a good knowledge of the hydrazono group and the effects it produces, compared with the carbonyl, on the protons of the carbon chain. It is possible to attain this objective by the NMR study of aliphatic and aromatic ketones and their arylhydrazones (ortho,para and diNO₂). The values of chemical shift of the ketone protons are used as reference, from which the following influences are shown: the identity of the proton studied (methyl, methylene or methyne); its position with respect to the hydrazone group (in α, β or γ); its substitution. The anisotropy of the nitrophenylhydrazono group thus demonstrated seems to be due firstly to the free pair of the double-bonded nitrogen, and secondly to the nitro group and its polarisation. The effects produced by the carbon and nitrogen chains on one another seem to indicate that the hydrogen-carrying nitrogen must possess a hybridisation near sp². Finally, the chemical shift of the proton linked with the nitrogen is very sensitive to the various substitutions of the molecule, which would seem to indicate its ‘sensor’ rôle in the α-carbonyl hydrazones.     

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.     

Constantes de couplage vicinales à travers deux hétéroatomes: III—Calculs théoriques et mesures expérimentales dans les hydrazides enrichies en 15N

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.     

Etude de composés d'addition des acides de Lewis XXVIII. Constantes de Hammett et vibration carbonyle des composés formés par TiCl4 et SbCl5 avec des chlorures de benzoyle parasubstitués

The adducts of benzoyl chlorides p-substituted by CH₃O? , CH₃? , and H? with the electronic acceptors SbCl₅ and TiCl₄ have been prepared, and the IR. absorption spectra of the solid products studied.     

Oxydations et halogénations régiosélectives et réactions carbéniques de dérivés de sucres portant un groupement thioéther

Regioselective Oxidations, Regioselective Halogenations and Carbene Reactions of Sugar Derivatives Bearing a Thioether Group Regioselective stoechiometrically controlled procedures are described for the oxidation of thiosugars either at the sulfur atom (to sulfoxides or sulfones) or at a hydroxymethylene group (to ketosugars). Ruthenium tetraoxide reacted at both sites. Chloration (SO₂Cl₂) of β-ketothioether sugar derivative 3 took place exclusively at C(6). Evidence is given that a chlorosulfonium intermediate C was formed when the dichloroketothiosugar derivative 6 was treated with SO₂Cl₂. The carbene generated from the tosylhydrazone 16 rearranged to the enoses 17–20 , the migrating group coming in equal proportions from C(4) and C(6). Some stereochemical aspects of these reactions are discussed.     

Spectres de rotation de la molécule de chlorobenzène : II. Variétés isotopiques multisubstituées et structure géométrique précise

In order to complete the r_s structure of chlorobenzene given in a preceding paper, a variety of isotopic species of this molecule were synthesized and their microwave spectra studied. This made twenty isotopic species available, enabling the determination of the geometrical parameters by a least squares method. Fitting only differences of moments of inertia either for monosubstituted species or to multiply substituted species gave the same result. They hardly differ from the r_o values and agree with the r_s values obtained by the Kraitchman equations. The resulting error limits were reduced, however.

The following structural parameters were obtained, C₁C₂ = 1.399 Å, C₂C₃ = 1.386 Å, C₃C₄ = 1.3976 Å, C₁Cl = 1.7248 Å, C₂H₂ = 1.080 Å, C₃H₃ = 1.081 Å, C₄H₄ = 1.081 Å, C₆C₁C₂ = 120° 16, C₁C₂C₃ = 119°78, C₂C₃C₄ = 120°24, C₃C₄C₅ = 119°80, C₁C₂H₂ = 119°45, C₂C₃H₃ = 119°76.

The structure of the ring differs significantly from C₆ symmetry. The deformation can be regarded as a compression of the position C₁ while the angle of C₂H₂ bond is also changed.     

17O-RMN. d'éthers,de cétones et d'esters cycliques. Détermination de constante de couplage quadrupolaire

¹³C- and ¹⁷O-relaxation times measured in cyclic ethers, cyclic ketones, and lactones allowed the determination of the quadrupolar interaction at the O-site. Values obtained for six-membered rings can be used as standard values for ethers (χ = 13 MHz), ketones (χ = 10.5 MHz), and esters (χ = 11.5 MHz for dicoordinated and 9.5 MHz for monocoordinated O-atom). Even within a series, no correlation is found between the ¹⁷O-chemical shift and the value of quadrupolar interaction.     

Interactions intramoléculaires. XXVII—Etudes structurales en série bicyclo[4.1.0]heptanique (effets d'anisotropie sur les déplacements chimiques du proton; constantes de couplage et équilibres conformationnels)

All the ¹H n.m.r. parameters of the following derivatives of 1,6-dimethylbicyclo[4.1.0]heptane are determined: 3,4-dimethoxycarbonyl (3 diastereoisomers), cis- and trans-3-methoxycarbonyl-2,2,5,5-d₄, cis- and trans-3-methyl-3-methoxycarbonyl; the cis- and trans-1,5,5-trimethylbicyclo[4.1.0]-3-heptanols are studied in the same way. The different chemical shifts are correlated with the aid of a collection of empiral increments. The conformational equilibria are determined from the vicinal coupling constants; the conformational free energies of the COOCH₃ group are evaluated; the part played by gauche interactions is considered.     

Composés d'addition des halogénures de niobium(V) et de tantale(V). VII. Composés du chlorure de niobium(V) avec l'oxytrichlorure et l'oxytribromure de phosphore

The adducts NbCl₅ · OPCl₃ and NbCl₅ · OPBr₃ are observed in chloroform solution by ³¹P-NMR spectroscopy. The enthalpy and entropy of activation for the exchange reaction between bulk and coordinated OPCl₃ are found equal to 17 ± 3 kcal/mole and 18 ± 10 cal/°mole. The stability of NbCl₅ · OPCl₃ is compared on a semi-quantitative basis to the stability of other adducts NbCl₅ · OPR₃ (R = Br, OMe, NMe₂).     

Analyse conformationnelle théorique des molécules de benzylidène-aniline, stilbène et azobenzène : Partie II. Résultats de la méthode PCILO et ajustement d''un potentiel empirique

A conformational study of the benzylidene-aniline stilbene and azobenzene isoelectronic molecules has been carried out by the PCILO method in terms of torsional angles, bond lengths and valence angles. Initially, the conditions of application of this method to highly conjugated molecules were defined. The optimized geometries are in good agreement with those determined in the gas phase. Furthermore the rotation around a Ф—N or Ф—C bond can be specifically related to the variation of the second-order correction to the energy. This term was used to adjust the torsional potential in an empirical method adapted to this kind of molecule and able to account for both theoretical and experimental results.     

Composés d'addition des halogénures de niobium(V) et de tantale(V) IV. Stabilité relative des composés de chlorures avec quelques nitriles

The relative stability constants of the adducts of MCl₅ (M ? Nb, Ta) with acetonitrile, halogenoacetonitriles, pivalonitrile, acrylonitrile and benzonitriles are determined in dilute solutions by NMR. methods. The stability of the adducts is controlled by inductive factors. Chemical shifts and analysis of the new compounds are reported.     

Composés d'addition des halogénures de niobium(V) et de tantale(V): VI. Réactions d'échange des composés du chlorure de niobium(V) avec quelques nitriles

The ligand exchange reactions NbCl₅·?N + RCN* ? NbCl₅ · RCN* + RCN are studied by NMR. spectroscopy for R = Me₃C, Me, FCH₂, CICH₂, BrCH₂, ICH₂. The reaction is of zero order in RCN and of first order in NbCl₅ · RCN and thus a dissociative mechanism is suggested for all the ligands studied. The enthalpies and entropies of activation are determined over 50° to 90° temperature ranges. There is a linear correlation between ΔG≠ and the free enthalpy of formation of NbCl₅ RCN. However this correlation is shown to hold only for series of adducts having the same donor group.