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The authors have reconsidered what is known about the structure of perylene and carried out some additional calculations concerning earlier gas diffraction work. They conclude that the length of the peri-bonds is now well established at 1.473 ± 0.005 A, which is the average of the gas-diffraction value (1.474 ± 0.014 A) and two X-ray results. This value does not differ significantly from theoretical values based on bond order-bond length relations.

Excluding enantiomers, there are 14 possible rotomeric conformations of 4-fluorobutan-1-ol, of which two are capable of forming an internal O−H···F hydrogen bond. The composition of the gaseous system is of special interest because it is determined by the energies of the conformers which reflect the energies of the hydrogen bonds. We have investigated the conformational composition of the gaseous system and the molecular structures of the conformers at 83 °C by gas-phase electron diffraction (GED) augmented by molecular orbital calculations. Because of the complexity of the 4-fluorobutan-1-ol system, the parameters of the several models tested were simplified by various constraints taken from the theoretical work. With these constraints, the best agreement with the GED data was obtained with a model consisting of about equal amounts of hydrogen-bonded and non-hydrogen-bonded conformers. Because the curled-up shape of the two forms capable, in principle, of forming internal hydrogen bonds is expected to be...

Evidence for internal hydrogen bonding has been sought for in a study of 1,4-butanediol (BDIOL), a molecule in which the «gauche» effect is expected to have minimal influence on the conformational preferences. This has been achieved by studying the molecular structure and the conformational equilibrium of the BDIOL molecule, using gas-phase electron diffraction (GED). Experimental data have been recorded at 60 keV at two different temperatures, 144 and 260 o C. The GED study has been supplemented by molecular mechanics calculations, carried out on the ten conformers that are in principle individually distinguishable by the GED method

Many organic C-nitroso compounds R-NO form stable dimers with a covalent NN bond. To gain insight into the dimerization reaction 2 R-NO ↓ (R-NO)2 a theoretical study of the dimerization to atrans-form was performed using HNO as a model compound. Complete geometry optimizations were carried out at the HF, MP2 and QCISD levels using a 6–31G* basis. In the stationary points energies were calculated at the MP4(SDTQ) and QCISD(T) levels. For the equilibrium structure of the monomer and dimers stable RHF solutions were found, whereas for the TS UHF and UMPn calculations were applied. Extensive spin contamination was found in the UHF wavefunction, and projections up tos+4 were invoked. Relative energies were corrected for differences in ZPE. Calculations were made (a) for the least-motion path (C 2h symmetry) and (b) for a path with complete relaxation of all internal coordinates. Along the latter path a TS having virtuallyC i symmetry was found. Along path (a) an activation energy of around 150 kcal/mol was predicted, in conformity with a symmetry forbidden reaction. On the relaxed path (b) the barrier to dimerization was estimated to be 10.7 kcal/mol at the MP4(SDTQ)//MP2 level, and 10.9 kcal/mol at the QCISD(T)//QCISD level. Unscaled ZPE corrections, calculated at the SCF level, changed these values to 12.7 and 12.9 kcal/mol, respectively. The reaction energy for the dimerization process is predicted to be − 17.2 kcal/mol at the MP4(SDTQ)//MP2 level corrected for ZPE. Calculations at the G1 level gave a corresponding value of − 16.4 kcal/mol. The equilibrium constant for the association to thetrans dimer is estimated to beK p =259 atm, indicating that the dimer should be an observable species in the gas phase.

Y 2 Cu 2 O 5 , a 20 K, cristallise avec le groupe d'espace Pna2 1 . Affinement de la structure jusqu'a 0,040

Bi 2 O(SO 4 ) 2 cristallise dans le systeme monoclinique avec le groupe d'espace c2/c. Affinement de la structure jusqu'a 0,069. La structure est constituee d'ions Bi 4 O 2 8+ presque plans et d'ions SO 4 2− relies pour former un reseau tridimensionnel au moyen de fortes liaisons oxygene bismuth-sulfate

Cristallisation dans Pbca avec affinement jusqu'a 0,043 pour les deux composes du titre. Le complexe anionique a une configuration pentagonale bipyramidale, avec le groupement peroxo situe dans le plan equatorial

A 86 K, le compose du titre cristallise dans le systeme triclinique avec le groupe d'espace P1. Affinement de la structure jusqu'a 0,027

Samples of the title phase with η ranging from ∼ 1 to ∼ 2.8 are studied XRD, neutron diffraction, XPS, and magnetic measurements.

C 10 H 12 N 4 OS cristallise dans le systeme monoclinique avec le groupe d'espace P2 1 /a. Affinement de la structure jusqu'a 0,041

[Cu(C 2 H 4 NO 3 ) 2 (H 2 O) 2 ]•2H 2 O cristallise avec le groupe d'espace Pbca. Affinement de la structure jusqu'a 0,0186

C 33 H 23 S 4 I 3 cristallise avec le groupe d'espace I2/c, et C 9 H 7 S 2 I 3 avec le groupe d'espace Ia. Affinement de la structure jusqu'a 0,05 pour les deux composes

Synthese des complexes Lu(CH 3 SO 3 ) 3 -2(3-picNO). Spectres IR montrant la coordination par les anions CH 3 SO 3 et par les nitrones. Pyrolyse dans l'air et l'azote

Le compose du titre cristallise dans le systeme monoclinique avec le groupe d'espace P1, a 92 K. Affinement de la structure jusqu'a 0,043

Cristallisation dans I4 avec affinement jusqu'a 0,042. Les liaisons hydrogene forment des quadrilateres le long des axes 4

Geometrie ab initio du compose dans l'etat gazeux ou solide, simulee par ordinateur. Bon accord avec les resultats experimentaux

Synthese des etudes cristallographiques realisees sur les composes d'addition 1:1 de l'hexafluorobenzene avec des hydrocarbures et des amines aromatiques. Dans tous les composes etudies, les molecules associees sont empilees alternativement en des colonnes infinies. Beaucoup de ces composes ont des structures cristallines desordonnees a temperature ambiante et forment des cristaux macles, les structures devenant ordonnees par refroidissement

DETERMINATION OF ACTIVITY - COMPOSITION RELATIONS IN (NI, MG)2SIO4 SOLID-SOLUTIONS AT 1200-1600-K BY SOLID-STATE EMF-MEASUREMENTS

Etude de l'effet des additifs CaCl 2 et CaBr 2 sur la reaction entre Ca 12 Al 14 O 33 et l'eau. L'hydrolyse est plus rapide en presence de CaCl 2 et CaBr 2 que dans l'eau pure