Search results for "hexane"
showing 10 items of 467 documents
Twisting of the resorcinarene core due to solvent effects upon crystallization
2009
The effect of the crystallization conditions on the conformation of the tetramethoxy resorcinarene skeleton was investigated in acetone solutions, to which was added a second component (less favorable solvent or salt) to promote crystallization. The resorcinarene core was found to adopt three different conformations: crown (I), a pinched crown (II) and a twisted pinched crown (III). In addition, the flexibility of the resorcinarene core was compared with a tetramethoxy resorcinarene derivative, resorcinarene bis-crown, which is in a fixed boat conformation.
Vitrification of polymer solutions as a function of solvent quality, analyzed via vapor pressures.
2006
Vapor pressures (headspace sampling in combination with gas chromatography) and glass transition temperatures [differential scanning calorimetry (DSC)] have been measured for solutions of polystyrene (PS) in either toluene (TL) (10-70 degrees C) or cyclohexane (CH) (32-60 degrees C) from moderately concentrated solutions up to the pure polymer. As long as the mixtures are liquid, the vapor pressure of TL (good solvent) is considerably lower than that of CH (theta solvent) under other identical conditions. These differences vanish upon the vitrification of the solutions. For TL the isothermal liquid-solid transition induced by an increase of polymer concentration takes place within a finite …
Preparation and Structures of Isoindolone- or Pyrimidone-Condensed Heterocycles Containing a Hydroxy Group on a Cyclohexane or Norbornane Moiety
2009
With DL-valinol, 3-amino-1-propanol and o-aminothiophenol, aroyl(bi/tri)cyclic lactones 1 and 2 were cy- clized to isoindole- 4-6, 8, 9, pyrimidinone- 10 or thiazepine- 7 condensed heterocycles. The ketal lactone 3 furnished the benzthiazoloisoindole 9 and mixtures of epimeric hydroxyphthalazinoquinazolinones 11 and 12. The structures were es- tablished by means of 1 H and 13 C NMR spectroscopy and in some cases by X-ray crystallography.
Free energy of solvation of solutes and their partition coefficients in methanol-water binary mixtures
2001
A method is presented that permits semiquantitative estimation of the partitioning of any solute between any two media. The method is adapted to the simulation of multicomponent solvents. As an example, the free energies of solvation ΔG solv,aq o in methanol-water binary mixtures and the partition coefficientsP for organic solvent—aqueous solvent were calculated. The organic solvents studied were 1-octanol, cyclohexane and chloroform. Linear relationships were observed between the relative dielectric constant and the volume fraction of methanol in mixtures with water. The four hydrocarbon models studied were hexane, cyclohexane, hexatriene and benzene. The results are in agreement with calc…
1984
Sedimentation coefficients of S of polystyrene covering a broad range of molecular weights M, are measured in toluene and 2-butanone in the semidilute regime. The results are compared with literature data using a plot of S · NA · η/(1 − νρ) = M · η/f versus concentration c, allowing experiments in different solvents of different density ρ and viscosity η to be compared (ν: partial specific volume of polymer; f: friction coefficient; NA: Avogadro number). According to scaling theory for concentrations higher than a critical concentration c, linear plots are to be expected. This is true for the theta-solvent cyclohexane, but for the theta-solvent cyclopentane as well as for the thermodynamica…
pH-Dependent ligands as carriers in transport experiments
2004
Abstract Conformationally pH-regulated ligands have been used as carriers in transport experiments. The experiments were carried out through bulky membranes and the pH at the source phase and at the receiving phase were modified to study the ability of ligands to act as pH-regulated carriers. The influence of pH on transport efficiency seems to be related to its influence on conformational equilibrium. X-ray determination of one precursor compound has been useful for determining the stereochemistry of one of the carriers. To cite this article: A.M. Costero et al., C. R. Chimie 7 (2004).
Application of Furan as a Diene: Preparation of Condensed 1,3-Oxazines by Retro-Diels−Alder Reactions
2004
(Di-exo-3-amino-7-oxabicyclo[2.2.1]hept-5-en-2-yl)methanol (3) was treated with oxo carboxylic acids [p-toluoylpropionic acid, cis- or trans-(p-toluoyl)cyclohexanecarboxylic acid, -benzoic acid or methanobenzocyclooctenecarboxylic acid] to furnish the oxanorbornene-fused pyrrolo[1,3]oxazine 4, the isoindolo[1,3]oxazines 5 and 6, and the methanobenzocyclooctenepyrrolo[1,3]oxazine 10, together with the retro-Diels−Alder products pyrrolooxazinone 7, oxazinoisoindolones 8 and 9, and oxazinopyrrolobenzocyclooctene 11. On reflux in chlorobenzene, furan was released from the oxanorbornene heterocycles 5 and 10 to give the retro-Diels−Alder products. The structures of the new compounds were establi…
(1S,2R,4S)-1-[(Benzylamino)methyl]-4-(prop-1-en-2-yl)cyclohexane-1,2-diol
2010
The title compound, C17H25NO2, was synthesized by epoxidation of the double bond of (S)-perillyl alcohol [(S)-4-isopropenyl-1-cyclohexenylmethanol], followed by the oxirane ring-opening by benzylamine using [Ca(CF3CO2)2] as catalyst under solvent-free condition at 313 K. The molecular conformation is stabilized by an intramolecular O—H...N hydrogen bond. In the crystal, molecules are linked by intermolecular N—H...O hydrogen bonds, forming chains parallel to the a axis, which are further connected by O—H...O hydrogen bonds into sheets parallel to (010). The absolute configuration of the molecule is known from the synthetic procedure.
Infusion mass spectrometry as a fingerprint to characterize varnishes in oil pictorial artworks.
2007
Mass spectrometry methodology to characterize drying oil used as binding media and varnishes in pictorial artworks, prior to conservation or restoration treatment, is proposed. The analytical treatment requires prior basic hydrolysis of the samples to release the fatty acids : caprylic, pelargonic, capric, sebacic, azelaic, suberic, eicosanoic, lauric, mirystic, palmitic, linolenic, linoleic, oleic and stearic, followed by separation from the matrix by a hexane/water extraction. After removing the solvent, the remaining solid is dissolved in potassium hydroxide, propanol and methanol. The mixture is directly infused into a mass spectrometer without any previous derivatization or separation …