Dynamique moléculaire du cristal ammoniac. Calcul ab initioSCF de l'energie electronique

The wave function and total energy of ammonia crystal are determined from the results of a totally optimized STO -3G ab initio calculation of the tetramer, pattern of the crystal. The crystal electronic energy is expressed in terms of the interatomic distances and charge density matrix elements. The geometry obtained from optimization of the tetramer energy on geometric parameters is in very good agreement with the experimental data of the crystal.     

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.     

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.     

Structure electronique de silacyclopentenes-2 et -3

Photoelectron spectroscopy is used to compare the electronic structures of 1,1′-dimethylsilacyclopent-3-ene, 1,1′-dimethylsilacyclopent-2-ene and several phenyl, vinyl and allyl derivatives. When a π orbital is on α position of the silicon atom, a hyperconjugation (α(SiC)π interaction) and a homoconjugation (p_πd_π interaction) are observed. The polarization induced by the P_πd_π interaction explains the differences of nucleophilic reactivity showed by the compounds studied. Also, the analysis of the shifts of first ionization potentials made it possible to propose a conformation for 1,1′-diallylsilacyclopent-3-ene.     

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.     

Un nouvel hétérocycle telluré: le benzisotellurazole-1,2. 2. Structure cristalline et moléculaire du benzisoselenazole-1,2 et du benzisotellurazole-1,2

Anomalous physical properties (solubility and melting point) of 1,2-benzisotellurazole are explained by very short intermolecufar Te…N bonds (2.4 Å) found in the crystal structure. Such bonds are not present in the crystal structure of 1,2-benzisoselenazole and the physical properties are those expected.     

Structures cristallines et moléculaires des muscs macrocycliques. I. La cis-civettone et les variétés polymorphes α et β de sa 2,4-dinitrophénylhydrazone

Crystal and Molecular Structure of Macrocyclic Musks. I. cis-Civetone and polymorphous α- and β-forms of his 2,4-dinitrophenylhydrazone cis-Civetone (C₁₇H₃₀O) forms tetragonal plastic crystals, space groupe 14¹; a = 9.95(4), c = 32.79(1) Å; Z = 8. The plastic phase exists in a wide temperature range and 731 reflexions could be collected at 153 K. The highly disordered structure model was obtained by the use of direct methods. The molecules appear as ring-shaped diffuse electron-density distributions located in special position. Two polymorphous crystalline forms were isolated for the 2,4-dinitrophenyl-hydrazone of cis-civetone (DNPHCC). Both forms are triclinic, space group P1 . Z = 2 (α-Form: a = 6.279(5), b = 12.605(8), c = 15.253(10) Å, α = 105.49(7). β = 100.31 (6), γ = 91.23(7)°; β-Form: a = 7.950(2). b = 8.405 (2). c = 18.233(4) Å, α = 100.28(2), β = 92.29(3), γ = 94.18(2)°). The structures were solved by direct methods and refined to R = 0.11. Each polymorph is associated with a different quinquangular conformation of the macrocycle. In the crystals the intermolecular interactions between macrocycles and aromatic substituents are minimized, the DNPH group being oriented in a face-to-face arrangement across a centre of symmetry. Empirical force field calculations show that the overall intluence of the DNPH moiety on the attached cycle does not significantly modify its conformation with regard to that of the ketone itself.     

Structure cristalline et moléculaire d'un dérivé méthyl-hexopyranoside à C(4) hybridé sp2

The derivative C₁₃H₁₉NO₅ crystallizes in space group P2₁2₁2₁ with a = 9.371, b = 11.815, c = 13.207 Å and Z = 4. The structure was solved by direct methods and refined by full-matrix least-squares to R = 0.058. The pyranose ring exists in the ³S₁ conformation (or in the equivalent, but here structurally less consistent, ⁰S₄ conformation). The dioxolane ring has an envelope conformation. Strong intramolecular interactions between the bulky substituents suggest that the ensuing strain energy is assumed, for a significant part, by the twisted-boat conformation of the pyranose ring.     

Interactions intramoleculaires. XXI—Constantes de couplage et interactions gauches avec un groupement t-butyle (molécules cyclohexaniques deutériées)

Different isotopic modifications of deuterated products of 1-t-butlyl-4-methoxycarbonyl cyclohexene (d₄-3,3,6,6), cis- and trans-3-methyl-4-cyanocyclohexene (d₃-3,6,6), cis- and trans-3-methyl-4-cyanocyclohexene (d₃,6,6), cis- and trans-3-t-butyl-4-methoxycarbonylcyclohexene (d₃,-3,6,6) are shown by nuclear magnetic resonance spectral analysis. By comparison of ³J and ⁴J coupling constants of model molecules and molecules with large gauche interactions, we obtain proof that the latter are in a chair conformation with moderate cycle deformations.     

Théorie quantique du pouvoir rotatoire magnétique des molécules diamagnétiques. II. Applications

The general formalism of the variational theory of the Faraday effect established in the first part of this paper is now applied to the actual computation of the Verdet constant of the hydrogen molecule, of water and of some saturated hydrocarbons. The numerical results have a correct order of magnitude and even, for hydrogen, are rather close to the experimental value.     

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.     

Etude thermodynamique des complexes de transfert de charge du type n-σ* en solution Complexes de la quinoléine et de quinoléines substituées avec I2, ICI et IBr

Thermodynamic study of charge transfert complexes (n-σ*) in solution Charge transfer complexes of quinoline and substituted quinolines (donors) with iodine, iodine chloride, and iodine bromide (acceptors) have been studied spectrophotometrically in CCl₄. The 1:1 stoechiometry of these complexes was verified by means of the continous variations method and the appearance of isosbestic points. Simultaneous determination of the equilibrium constant and enthalpy of adduct formation was carried out by calorimetry. It was observed for every donor that the equilibrium constants of the complexes studied increase with the strength of the acceptors. A linear correlation between enthalpy of adduct formation and donor strength was obtained only for the complexes Donor ICI.     

Constitution moléculaire d'α,ω-difluoropolydiméthyl-N-méthylsilazanes. Equilibres obtenus par une réaction de redistribution

Unlike the α,ω-dihalogenopolydimethylsiloxanes, the α,ω-dichloropolydimethyl-N-methylsilazanes show a net preference for cyclic species with respect to linear structures at equilibrium. The aim of this study is to evaluate the perturbations in the molecular constitution of these α,ω-dihalogenopolydimethyl-N-methylsilazanes resulting from the substitution of the terminal chlorine atoms by fluorine atoms. This polymeric family was prepared by reacting (CH₃)₂SiF₂ with nonamethylsilazane [(CH₃)₂SiNCH₃]₃. The redistribution of the fluorine atoms with the bridging methylimino groups reached an equilibrium after about 5 months' heating at 150°C for all the samples prepared. The relative abundance of the various molecular species and fragments at equilibrium was deduced from the quantitative analysis of the proton nuclear magnetic resonance (NMR) spectra. The molecular constitution at equilibrium is described by two constants. The first, K = [neso] [middles in chains]/[terminal moieties]² = (2.8 ± 0.8) 10^?2, shows that the presence of terminal fluorine atoms is unfavorable to the formation of short chains. On the other hand, the trimeric cyclic species [(CH₃)₂SiNCH₃]₃ are found to be highly favored (K°₃ = 550 ± 100 mole/liter). These observations further confirm that the equilibrium constants which control the noncyclic part of polymeric families depend little on the functionality of the substituents exchanged [for example, on changing from ? N(CH₃)₂ to ? NCH₃? ] when the reorganization heat order is one.     

Nature et stabilité des complexes métalliques de cryptands dinucléants en solution. I. Polyazapolyoxa macrotricycle cylindrique et monocycle constitutif

Nature and Stability of Some Metallic Complexes of Dinucleating Cryptands in Solution. I. A Polyazapolyoxa Cylindrical Macrotricycle and its Monocyclic Subunit pH-metry and UV spectrophotometry were used to study the complexing properties of the cylindrical macrotricycle, 1,7,13,19-tetraaza-4,16-dioxa-10,22,27,32-tetraoxatricyclo[17.5.5.5]tetratriacontane ( 1 ) and of its constitutive monocyclic subunit, 1,7-diaza-4,10-dioxacyclododecane ( 2 ) with some transition and heavy metal cations (Cu²⁺, Co²⁺, Ni²⁺, Zn²⁺, Cd²⁺, Pb²⁺, Ag⁺), in aqueous medium 0.1M Et₄NClO₄, at 25°. The protonation constants of the ligands as well as the nature and the stabilities of the complexes formed in the pH-regions studied were determined. The tricycle 1 only formed dinuclear M₂L complexes with Cu²⁺, Zn²⁺, and Ag⁺, accompanied in the latter case by a protonated mononuclear MLH species, and with Cu²⁺ and Zn²⁺ at high pH-values by dinuclear hydroxo complexes. Only mononuclear complexes were evidenced with the other cations, ML being accompanied either by protonated or hydroxy mononuclear species. The mononuclear complexes of 1 , when they existed, were more stable than the corresponding complexes of 2 , except for cobalt which formed complexes of comparable stability with both ligands. In the other cases (Cd²⁺, Pb²⁺, Ag⁺), the stability differences between the complexes of 1 and 2 increased with the size of the cation.