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showing 10 items of 3423 documents
On the Formation and Desolvation Mechanism of Organic Molecule Solvates: A Structural Study of Methyl Cholate Solvates
2017
Solvate formation and the desolvation mechanism of 25 obtained methyl cholate solvates were rationalized using crystal structure analysis and study of the phase transformations. The facile solvate formation was determined to be associated with the possibility for more efficient packing in structures containing solvent molecules. Most of the obtained solvates crystallized in one of the six isostructural solvate groups, with solvent selection based on the solvent capability to provide particular intermolecular interactions along with appropriate size and shape. In crystal structures several different methyl cholate conformers were observed, as apparently more efficient packing could be achiev…
Hydrogen bond studies on n-pentanol and 2-methyl-2-butanol by Raman spectroscopy
1986
Polarized Raman spectra of n-pentanol and its isomer 2-methyl-2-butanol are obtained in the liquid phase near the melting points and at superheated temperatures. The measurements are performed in the intramolecular O-H stretching region. Our analysis of the Raman data provides an interpretation of the spectral features in terms of symmetric O-H bands, originated by various degrees of intermolecular coupling, for which mechanism is different for the two isomers. Temperature dependence of the spectra is also discussed in terms of available structural and dynamical models for these H-bonded liquids.
Structural characterization of β-2′-pyridylaminocrotonoyl-2-pyridylamide by ESI-MS, NMR, single crystal X-ray analysis and ab initio methods
2003
Abstract In contradiction with earlier reports 1H, 13C and 15N NMR spectra show that β-2′-pyridylaminocrotonoyl-2-pyridylamide is the only form present in chloroform solution. According to the X-ray data the same tautomer exists also in the crystal state. The studied amide has a dimeric form where the monomer molecules are held together by two intermolecular hydrogen bonds. The NMR spectral data show that there is also an intramolecular hydrogen bond in each monomer subunit. The dilution experiments and variable-temperature 1H NMR runs show that β-2′-pyridylaminocrotonoyl-2-pyridylamide tends to form the dimers also in chloroform solution at higher concentrations. The ESI-TOF MS measurement…
Conformational properties of methylene bridged resorcarenes
1998
Abstract Conformations and conformational interconversions of resorcarene 1c have been studied by molecular mechanics calculations. As with calix[4]arenes the general stability of the four basic conformations is cone > partial cone > 1,2-alternate > 1,3-alternate. The lowest energy is calculated for a pinched cone conformer with C2v symmetry stabilised by intramolecular hydrogen bonds of the two “parallel” resorcinol units as donors. The topomerisation of the cone conformation proceeds via the partial cone and 1,2-alternate intermediates with a calculated barrier of 9.9 kcal mol−1 which is in excellent agreement with the experimental value.
Hexachlororhenate(IV) salts of ruthenium(III) cations: X-ray structure and magnetic properties
2012
Abstract Two novel rhenium(IV)–ruthenium(III) compounds of formulae [RuCl(NH3)5]2[ReCl6]Cl2 (1) and [RuCl2(en)2]2[ReCl6]·2CH3CN (2) (en = 1,2-ethylenediamine) have been prepared and characterized. Their crystal structures were determined by single-crystal X-ray diffraction. 1 crystallizes in the monoclinic system with C2/m as space group, whereas 2 crystallizes in the triclinic system with space group P(−1). The crystal structures of 1 and 2 are made up of discrete [ReCl6]2− anions and [RuCl(NH3)5]2+ (1) or [RuCl2(en)2]+ (2) cations held together by N–H···Cl hydrogen bonds, van der Waals and electrostatic forces. The magnetic properties were investigated from susceptibility measurements per…
N-Benzyl-2,3,4,5,6-pentafluorobenzamide
2010
In the title compound, C14H8F5NO, the dihedral angle between the planes of the pentafluorophenyl and phenyl rings is 18.34 (5)°. An intermolecular N—H...O hydrogen bond between the amide groups connects these molecules to form an infinite chain through the crystal structure. One weak intermolecular C—H...O contact and one π–π interaction [centroid–centroid distance = 3.772 (3) Å] are also involved in crystal structure stabilization between the phenyl rings.
Structural and spectroscopic characterisation of 2-(2'-hydroxybenzoyl)pyrrole and its O-methyl derivative
2004
Abstract Density functional theory calculations on the tautomeric and conformational equilibria of 2-(2′-hydroxybenzoyl)pyrrole (HBP) and 2-(2′-methoxybenzoyl)pyrrole (MBP) were performed. Moreover, the experimental IR and UV spectra of the same compounds were recorded and compared with the theoretical data. The presence of an intramolecular hydrogen bond in HBP can be related to the biological activities of some of its derivatives.
Kinetically Trapped Supramolecular Assembly of Perylene Dianhydride Derivative in Methanol: Optical Spectra, Morphology, and Mechanisms.
2016
Supramolecular self-assembly has attracted increasing attention as a breakthrough methodology in the fields of nanoscience and nanotechnology. Herein, a perylene dianhydride derivative (TP-PDA) self-assembles into well-defined nanospheres through a nucleation-growth process. The mechanisms of this process were explored by using spectral analysis, dynamic light scattering (DLS), and scanning electron microscopy (SEM). In situ DLS and in situ SEM both revealed that the size of the aggregated nanospheres increases with time until the formation of equilibrium H-aggregates. This shows that TP-PDA undergoes a kinetically trapped assembly with a rapid transformation into the thermodynamically favo…
Molecular and crystal structure of Ac-(Z)-ΔAbu-NMe2 and Ac-DL-Abu-NMe2 as compared to those of related molecules
2004
Abstract The molecular and crystal structures of two homologous amino acid derivatives: N-acetyl-α,β-dehydro-butyrine N´,N´-dimethylamide (1) and N-acetyl-DL-butyrine N´,N´-dimethylamide (2), have been determined by X-ray crystallography. Similar solid-state association of both compounds is observed; despite different molecular conformation, they form centrosymmetric dimers linked by the intermolecular N–H…O hydrogen bonds. The conformation of two crystallographically independent molecules of 1 [with torsion angles ϕ, ψ, χ 1 ≈ (–47°, 130°, 3°), respectively] is also characteristic of other related diamides – ΔAla, ΔPhe and ΔLeu – previously studied in the solid state. To analyse whether thi…
Topological control in the hydrogen bond-directed self-assembly of ortho-, meta-, and para-phenylene-substituted dioxamic acid diethyl esters
2010
[EN] The structures of the series of N,N¿-1,n-phenylenebis(oxamic acid ethyl ester) molecules with n = 2 (H2Et2opba, 1), 3 (H2Et2mpba, 2), and 4 (H2Et2ppba, 3) have been determined by single-crystal X-ray diffraction (XRD) methods. Density functional (DF) calculations have been performed on the simplest model system N-phenyloxamic acid methyl ester (HMepma). Compounds 1¿3 have either folded (H2Et2opba), bent (H2Et2mpba), or linear (H2Et2ppba) almost planar (periplanar) molecular configurations with the two oxalamide moieties being slightly tilted up and down, respectively, with respect to the benzene ring. The energy calculations as a function of the torsion angle (¿) around the N(amide)¿C(…