Dielectric properties of three‐ring fluorinated compounds

Four three‐ring compounds, consisting of two cyclohexyl rings and one mono‐ or difluorinated phenyl ring, were studied using dielectric spectroscopy methods over a broad frequency range (1 kHz–3 GHz). They exhibit a nematic phase in a broad temperature interval, enriched by a smectic B phase in one case. The static and dynamic dielectric properties were analysed. It was established that the bridging CH₂CH₂ group placed between cyclohexyl and phenyl rings considerably changes the reference frame of the molecule, unlike the situation when it links two cyclohexyl rings. In the nematic and smectic B phases the motion around the short axis is a Debye process, whereas the rotation around the long axis is split into two processes: independent rotation of the whole molecule and its fluorophenyl part.     

Thermal decomposition of dicyclopentadienylarylvanadium compounds

The thermolysis of compounds of the type Cp₂VR (R = aryl) in the solid state has been studied. A distinct increase in thermal stability is observed upon substitution of the ortho-position of the aryl group. Thermal decomposition occurs with formation of RH, Cp₂ V, a vanadocene homologue with the group R substituted in one of the Cp rings and, probably, a vanadocene homologue with two substituted Cp rings. It is shown that the abstraction of the hydrogen atom from the cyclopentadienyl ring, necessary for the formation of RH, is an intermolecular process, whereas the substitution of the aryl group in the Cp ring is intramolecular. A decomposition mechanism is proposed in which the group R is transferred from the vanadium atom to the C₅H₅ ring of the same molecule by interaction with an aryl group of another molecule. The thermal decomposition of Cp₂VR is compared with that of the analogous titanium compounds.     

Theoretical study of C24N4 molecule

Both ab initio 6-31G, 3-21G and STO-3G basis sets and semiempirical PM3 and AM1 molecular orbital calculations are carried out on the C₂₄N₄ molecule of the T_d symmetry group. Results on the fully optimized structure which constrained T_d symmetry, molecular orbitals and vibrational frequency were obtained by both ab initio and semiempirical methods. The binding energy and various thermodynamic properties were also calculated via the PM3 and AM1 semiempirical methods. All the evidence of this work proves that the C₂₄N₄ molecule is stable and that its four six-membered rings with a remarkable delocalized C…C bond are similar to the related rings in the C₆₀ buckminsterfullerene structure.     

The crystal and molecular structure ofexo-1,7-dichloro-8,8,9,9,10,10-hexafluoro-3,4-benzotricyclo[5.3.0.02,6]decene-3

The crystal structure of the title molecule has been determined by single crystal X-ray diffraction method. The molecule crystallizes in the orthorhombic space group Pbca with unit-cell dimensions a = 21.872(8), b = 11.815(6), c = 10.785(6) Å, and Z = 8. The structure has been solved by MULTAN and refined by least-squares calculations to R = 7.62% for 2088 reflections measured by a diffractometer. The molecule has the exo configuration. The central cyclobutane ring is nearly planar. The two five-membered rings are of the envelope conformation. The dihedral angle between the cyclobutane ring and the terminal five-membered ring is 75.5° and that between the cyclobutane ring and the other five-membered ring is 62.2°.     

New liquid-crystalline isothiocyanates with high clearing points, low viscosities and strong nematic character

Bi-, tri- and tetra-ring liquid-crystalline compounds with an isothiocyanate group in the terminal position of the molecule and with an ethylene group in the central position have been synthesized. Phenyl, cyclohexyl, bicyclo[2,2,2]octyl, 1,3-dioxane and pyrimidinyl were used as the ring systems. Their transition temperatures and melting enthalpies have been determined. The relationship between the order of the rings in the molecule and the clearing points and melting points of the compounds is discussed. It is shown that these compounds are valuable components of liquid crystal mixtures, since they effectively raise their clearing points yet only have a small effect on the viscosity.     

Structure of a C26H28 alkene formed via titanium-promoted reductive dimerization of 4-(spirocyclopropyl)-pentacyclo[5.4.0.02,6.03,10.05,9]undecan-8-one

A spiro-fused C₂₆H₂₈ cage≓ dimer hydrocarbon contains two three-membered rings, two four-membered rings, eight five-membered rings, and two six-membered rings. The molecule is calculated by molecular mechanics to have 902 kJ/mol of strain energy distributed primarily between angle strain (457 kJ/mol) and torsional interactions (368 kJ/mol). Molecular mechanics calculations and a geometry-optimized ab initio calculation are used to analyze the bond lengths and bond angles in the molecule. There is one major discrepancy between observed and calculated distances.     

Study of the crystal structure of binuclear boron difluoride acetylacetonate

The molecular and crystal structure of binuclear boron difluoride acetylacetonate, in which two boron chelate moieties are linked by a disulfide group, is determined. It is found that in the crystalline state, the chelate moieties are non-equivalent. The differences identified stem from the fact that molecules crystallize in pairs: two chelate ring (one from each molecule of the pair) are linked with each other by the stacking interaction. The other chelate rings of the pair do not participate in intermolecular interactions.     

Chiral spherical molecule constructed from aromatic amides: facile synthesis and highly ordered network structure in the crystal

A novel chiral spherical molecule composed of aromatic amide was synthesized in short steps. The molecule is constructed from four benzene rings connected by six amide bonds and has multiple functionalizable points and an asymmetric structure. The racemic spherical molecule constructed channel network structures in the crystalline state.     

(E)‐4,4′‐Bis(1,3‐benzoxazol‐2‐yl)stilbene at 150 and 375 K

The title compound, a chromophore of formula C₂₈H₁₈N₂O₂, crystallizes with the molecule lying on an inversion centre to give one‐half of a crystallographically independent molecule in the asymmetric unit. The molecule is almost planar, with slight deviation of the benzene rings from the mean molecular plane. The structure is characterized by a herringbone packing arrangement arising from C—H...π and π–π intermolecular interactions. The benzoxazole group is disordered between two orientations, with occupancy factors of 0.669 (10) and 0.331 (10) at 150 K [0.712 (7) and 0.288 (7) at 375 K].     

Bildung siliciumorganischer Verbindungen. 95. Die Kristallstruktur eines Hexadecamethyl-octasila-dispiro-[5.1.5.1]-tetradecans,Si8C22H65

Formation of Organosilicon Compounds. 95. Crystal Structure of a Hexadecamethyloctasila-dispiro [5.1.5.1]tetradecane, Si₈C₂₂H₅₆ 1,1,3,3,5,5,7,7,9,9,11,11,13,13,14,14-Hexadecamethyl-1,3,5,7,9,11,13,14-octasila-dispiro[5.1.5.1]tetradecane crystallizes monoclinically in the space group P2₁/n (No. 14) with a = 1352.4 pm, b = 1215.5 pm, c = 1001.2 pm, β = 92.11° and Z = 2 molecules per unit cell. The dispiro system is formed by a central disilacyclobutane and two C-spiro connected trisilacyclohexane rings. The symmetry of the molecule is 2/m, with flattened six membered rings in chair conformation. The Si? C bonds are enlarged (192 pm) at the strained spiro region whereas the Si? C bonds are distinctly shortened (186 pm) at the opposite Si atoms in the six membered rings.     

Mesoscale Surface Patterning of a Laterally‐Grafted Rod Amphiphile: Rings And Fibers

An aromatic amphiphilic molecule based on branched oligo(ethylene oxide) was synthesized. Evaporation‐driven ring formation and Langmuir–Blodgett films are investigated by utilizing this rigid–flexible block molecule. The size of the rings is strongly dependent on the solvent evaporation rate and the concentration of the molecule. In case of fast evaporation, volcano‐like rings are formed by evaporating solution of high concentration. Perfectly symmetrical rings with diameters in the range of 2–6 μm are obtained by evaporating solution of low concentration. The formation mechanism of the ring is briefly discussed. The molecule at the air–water interface exhibits excellent amphiphilic properties. Upon transferring the monolayer onto solid substrates, AFM revealed the formation of fine and long, straight fibers. By combining the data obtained from the isotherms, AFM, water contact angle measurements, and UV/Vis and fluorescence spectra, the fibers are suggested to be formed by π–π stacking interaction of the aromatic rod segments as the oligo(ethylene oxide) branches are submerged in the water subphase upon compression. The fiber formation is associated with the transformation of the aromatic rod segments from the face‐on conformation to the edge‐on conformation.     

Structure and decompression melting of a novel, high-pressure nanoconfined 2-D ice

Molecular dynamics (MD) simulations of water confined in nanospaces between layers of talc (system composition Mg(3)Si(4)O(10)(OH)(2) + 2H(2)O) at 300 K and pressures of approximately 0.45 GPa show the presence of a novel 2-D ice structure, and the simulation results at lower pressures provide insight into the mechanisms of its decompression melting. Talc is hydrophobic at ambient pressure and temperature, but weak hydrogen bonding between the talc surface and the water molecules plays an important role in stabilizing the hydrated structure at high pressure. The simulation results suggest that experimentally accessible elevated pressures may cause formation of a wide range of previously unknown water structures in nanoconfinement. In the talc 2-D ice, each water molecule is coordinated by six O(b) atoms of one basal siloxane sheet and three water molecules. The water molecules are arranged in a buckled hexagonal array in the a-b crystallographic plane with two sublayers along [001]. Each H(2)O molecule has four H-bonds, accepting one from the talc OH group and one from another water molecule and donating one to an O(b) and one to another water molecule. In plan view, the molecules are arranged in six-member rings reflecting the substrate talc structure. Decompression melting occurs by migration of water molecules to interstitial sites in the centers of six-member rings and eventual formation of separate empty and water-filled regions.     

Crystal Structure and Molecular Orbital Calculation of（1R，2S）－N－Methylephedine Benzoate Hydrochloride

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Polymorphic forms of lupane triterpenoid betulonic aldehyde (betulonal)

The lupane triterpenoid betulonic aldehyde [also known as betulonal; systematic name: lup‐20(29)‐en‐28‐al‐3‐one, C₃₀H₄₆O₂] is a product of betulin oxidation. Crystals were obtained from hexane [form (I)] and dimethyl sulfoxide [form (II)] solutions. Forms (I) and (II) are both orthorhombic. The molecular geometric parameters in the two forms are similar, but the structures are different with respect to the crystal packing. Polymorph (I) contains two independent molecules in the asymmetric unit, while polymorph (II) contains only one molecule, which has a disordered aldehyde group [the disorder ratio is 0.769 (4):0.231 (4)]. In each molecule, the six‐membered rings have chair conformations, whereas the cyclopentane ring in each molecule adopts an envelope conformation. All the rings in the lupane nucleus are trans‐fused. The extended structures of both polymorphs are stabilized by weak intermolecular C—H...O and van der Waals interactions. Weak intramolecular C—H...O interactions are also observed.     

NMR studies of conformations and dynamic processes—III : Cyclophanes with unsaturated bridges

Three cyclophanes, each displaying a different type of dynamic process, have been studied by NMR methods. The barriers to these processes are attributed mainly to the decrease in π-electron overlap between the benzene rings and adjacent double bonds which occurs in the transition state for each process. In [5₂] paracyclophanetetraene, two successive flippings of the benzene rings interconvert the two hydrogens in the methylene groups (Scheme 1). In tetramethyl [2₄] paracyclophanetetraene, the passage of one methyl group through the central cavity of the molecule interconverts two conformations of similar, but not equal, free energy (Scheme 2). In [2₆] orthoparacyclophanehexaene, the orthosubstituted rings change sides by passing through the centre of the cyclophane (Scheme 3).     

Effects of the covalent linker groups on the spin transport properties of single nickelocene molecules attached to single-walled carbon nanotubes

The understanding of how the spin moment of a magnetic molecule transfers to a carbon nanotube, when the molecule is attached to it, is crucial for designing novel supramolecular spin devices. Here we explore such an issue by modeling the spin transport of a single-walled carbon nanotube grafted with one nickelocene molecule. In particular we investigate how the electron transport becomes spin-polarized depending on the specific linking group bonding nickelocene to the nanotube. We consider as linkers both aziridine and pyrrolidine rings and the amide group. Our calculations show that, at variance with aziridine, both pyrrolidine and amide, do alter the sp(2) character of the binding site of the nanotube and thus affect the transmission around the Fermi level. However, only aziridine allows transferring the spin polarization of the nickelocene to the nanotube, whose conductance at the Fermi level becomes spin-polarized. This suggests the superiority of aziridine as a linker for grafting magnetic molecules onto carbon nanotubes with efficient spin filtering functionality.     

Fourier-transform infrared spectroscopic studies of dithia tetraphenylporphine

We present here infrared absorption spectra of dithia tetraphenylporphine and its cation in the 450–1600 and 2900–3400 cm⁻¹ regions. Most of the allowed IR bands are observed in pairs due to overallD _2h point group symmetry of the molecule. The observed bands have been assigned to the porphyrin skeleton and phenyl ring modes. Some weak bands, which are forbidden underD _2h , also appear in the spectra due to the distortion of the molecule from planarity-caused by the out-of-plane positioned N and S atoms. Increased intensity of some phenyl ring bands compared to free-base tetraphenylporphine is explained on the basis of rotation of phenyl rings towards the mean molecular plane. Contrary to the point group symmetry of cation of dithia tetraphenylporphine, certain bands are observed to be degenerate due to identical bonding arrangements in pyrrole rings of the cation     

New liquid-crystalline isothiocyanates with high clearing points,low viscosities and strong nematic character

Abstract

Bi-, tri- and tetra-ring liquid-crystalline compounds with an isothiocyanate group in the terminal position of the molecule and with an ethylene group in the central position have been synthesized. Phenyl, cyclohexyl, bicyclo[2,2,2]octyl, 1,3-dioxane and pyrimidinyl were used as the ring systems. Their transition temperatures and melting enthalpies have been determined. The relationship between the order of the rings in the molecule and the clearing points and melting points of the compounds is discussed. It is shown that these compounds are valuable components of liquid crystal mixtures, since they effectively raise their clearing points yet only have a small effect on the viscosity.     

Benzenoid rings resonance energies and local aromaticity of benzenoid hydrocarbons

In this article, we consider partitioning of the analytical expression for resonance energy (RE) in smaller benzenoid hydrocarbons, to individual benzenoid rings of polycyclic molecules. The analytical expression for molecular RE, available since 1976, is given by the count of all linearly independent conjugated circuit in all Kekulé structures in a molecule. Analytical expression for local ring RE (RRE) is given by counting all linearly independent conjugated circuits involving single benzenoid ring in all Kekulé structures, which when added, gives the molecular RE. If for benzene ring the RRE is taken to be 1.000, rings in polycyclic benzenoid hydrocarbons have their ring RRE, which give the degree of their local aromaticity, smaller than 1.000. The difference to 1.000 is a measure of the similarity of a ring to benzene in this one-dimensional (1-D) representation of local aromaticities of benzenoid hydrocarbons. The plot of RRE against the distance of the same ring from benzene in the Local Aromaticity Map, in which benzenoid rings are characterized ring bond orders and average variations of adjacent CC bonds, shows linear correlation (with r = 0.91), reducing the local aromaticity in benzenoid hydrocarbons to 1-D molecular property. © 2018 Wiley Periodicals, Inc.     

Kristall- und Molekülstruktur von Bis[N-(diethylaminothiocarbonyl)-N′-phenylbenzamidinato]kupfer(II)

Crystal and Molecular Structure of Bis[N-(diethylaminothiocarbonyl)-N′-phenyl-benzamidinato]copper(II) The structure of bis[N-(diethylaminothiocarbonyl)-N′-phenyl-benzamidinato]-copper(II) has been determined by X-ray structure analysis. The compound crystallizes in the orthorhombic space group Pbca with a = 27.792, b = 19.197, c = 12.325 Å and 8 formula units per unit cell. The structure was solved by heavy atom technique. The final R value was R = 0.06 for 1589 observed symmetry independent reflections. The coordination polyhedron is a distorted tetrahedron. In spite of the bulky phenyl groups the ligator atoms are arranged in cis position. The chelate rings deviate clearly from planarity. The phenyl rings are appreciably twisted against the chelate rings.