A new structural type of liquid crystal Crystal structures and thermotropic mesophases of dihydroxytetraalkyldisiloxanes: Columnar phases with hydrogen bonded assemblies

Abstract

Previous structural investigations of mesogenic organosilicon compounds (1, 3-dihydroxytetraalkyldisiloxanes, [R₂(OH)Si]₂O, R = C _n H_2n+1) which form thermotropic phases are outlined. The crystal and molecular structure determination of a non-mesogenic member of this series [Me₂(OH)Si]₂O is described. It is inferred that the mesophases formed by this family of compounds belong to a new structural type with columnar stacks of the molecules laced together with hydrogen bonds.     

Michael condensation of 3-arylidene-3H-pyrrol-2-ones and 3-arylidene-3H-furan-2-ones with cyclohexanone

The Michael condensation in the series of 5-aryl-3-arylidene-3H-pyrrol-2-ones and 5-aryl-3-arylidene-3H-furan-2-ones, containing an activated C=C bond, with cyclohexanone was investigated. It was shown that the condensation products were 1,5-dicarbonyl compounds containing a heterocyclic fragment. The enolization of one of the oxo groups, leading to the formation of hydroxypyrrole or hydroxyfuran structures, was demonstrated by the spectral data. __________ Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 6, pp. 823–827, June, 2007.     

Esterification of n-Butanol with Acetic Acid in the Presence of Heteropoly Acids with Different Structures and Compositions

The esterification reaction of n-butanol with acetic acid ([BuOH] : [HOAc] = 1 : 15 mol/mol; 55°C, 5% H₂O) was studied in the presence of tungsten heteropoly acids of the Keggin (H₃PW₁₂O₄₀, H₄SiW₁₂O₄₀, H₅PW₁₁TiO₄₀, H₅PW₁₁ZrO₄₀, and H₃PW₁₁ThO₃₉) and Dawson structure (-H₆P₂W₁₈O₆₂, H₆P₂W₂₁O₇₁(H₂O)₃, H₆As₂W₂₁O₆₉(H₂O), and H₂₁B₃W₃₉O₁₃₂). The reaction orders with respect to H₆P₂W₂₁O₇₁(H₂O)₃, H₃PW₁₂O₄₀, and H₆P₂W₁₈O₆₉are equal to 0.78, 1.00, and 0.97, respectively. It was found that the reaction rate depends on the acidity, as well as on the structure and composition of heteropoly acids. The H₂₁B₃W₃₉O₁₃₂heteropoly acid is most active, whereas the Keggin-structure heteropoly acids exhibit the lowest activities. Of the Keggin structure heteropoly acids, H₅PW₁₁ZrO₄₀exhibits the highest activity because of the presence of a Lewis acid site in its structure.     

Polarity of Thymine and 6-Methyluracil-Modified Porous Polymers,According to Data from Inverse Gas Chromatography

Russian Journal of Physical Chemistry A - The affinity of surfaces of porous polymer Polysorb-1 samples modified with thymine (5-methyluracil) and 6-methyluracil toward sorbates capable of various...     

n‐Dopants Based on Dimers of Benzimidazoline Radicals: Structures and Mechanism of Redox Reactions

Dimers of 2‐substituted N,N′‐dimethylbenzimidazoline radicals, (2‐Y‐DMBI)₂ (Y=cyclohexyl (Cyc), ferrocenyl (Fc), ruthenocenyl (Rc)), have recently been reported as n‐dopants for organic semiconductors. Here their structural and energetic characteristics are reported, along with the mechanisms by which they react with acceptors, A (PCBM, TIPS‐pentacene), in solution. X‐ray data and DFT calculations both indicate a longer C?C bond for (2‐Cyc‐DMBI)₂ than (2‐Fc‐DMBI)₂, yet DFT and ESR data show that the latter dissociates more readily due to stabilization of the radical by Fc. Depending on the energetics of dimer (D₂) dissociation and of D₂‐to‐A electron transfer, D₂ reacts with A to form D⁺ and A^? by either of two mechanisms, differing in whether the first step is endergonic dissociation or endergonic electron transfer. However, the D⁺/0.5 D₂ redox potentials—the effective reducing strengths of the dimers—vary little within the series (ca. ?1.9 V vs. FeCp₂^+/0) (Cp=cyclopentadienyl) due to cancelation of trends in the D^+/0 potential and D₂ dissociation energy. The implications of these findings for use of these dimers as n‐dopants, and for future dopant design, are discussed.     

Reductive Elimination at Pb(II) Center of an (Amino)plumbylene-Substituted Phosphaketene: New Pathway for Phosphinidene Synthesis

A stable (amino)plumbylene-substituted phosphaketene 3 was synthesized by the successive reactions of PbCl₂ with two anionic reagents (lithium amidophosphine and NaPCO). Of particular interest, the thermal evolution of 3 , at 80 °C, leads to the transient formation of corresponding amino- and phosphanylidene-phosphaketenes ( 6 and 7 ), via a reductive elimination at the Pb^II center forming new N−P and P−P bonds. Further evolution of 6 gives a new cyclic (amino)phosphanylidene phosphorane 4 , which shows a unique reactivity as a phosphinidene. This result provides a new synthetic route to phosphinidenes, extending and facilitating further their access.     

Orientational processes in the yarns of high-molecular-mass cellulose acetate in vapors of nitromethane and its mixture with water

The phenomenon of spontaneous changes in the linear dimensions (elongation-contraction) is described for commercial and laboratory samples of acetate yarns processed by wet spinning from high- molecular -mass cellulose diacetate in vapors of a mesophas ogenic solvent (which is able to form a lyotropic LC phase with the polymer), nitromethane, and its mixtures with water. The thermodeformational, elastic- plastic, physicomechanical, and surface characteristics of the yarns at different stages of their spontaneous deformation are analyzed. When samples are treated with probe vapors, orientational processes in the polymer matrix are activated, and this observation makes it possible to prepare yarns with improved physicomechanical characteristics and with low linear density. A new phenomenon (to our knowledge) of cyclic three- stage deformation of acetate monofilaments in nitromethane vapors is discovered. This evidence is interpreted from the standpoint of phase (amorphous glassy-liquid crystalline state) and conformational transitions as well as by the mechanism of interaction between polymers and solvent vapors and related development of the LC phase.     

Polymers based on ionic monomers with side phosphonate groups

A number of new ionic vinyl monomers composed of 1-vinylimidazolium cation with diethoxy- and dihydroxyphosphoryl groups and various anions—Br^?, (CN)₂N^?, and (CF₃SO₂)₂N^?—are synthesized. The free-radical polymerization of the monomers in solutions of molecular and ionic solvents yields new polymer analogs of ionic liquids, and their molecular-mass characteristics, solubility, heat resistance, thermal stability, and electrical conductivity are estimated. It is shown that the incorporation of bulky phosphorylalkyl side substituents into the vinylimidazolium polycation causes a decrease in the glass-transition temperature and an increase in the ionic conductivity of polymer salts. The highest ionic conductivity (2.6 × 10^?5 S/cm at 25°C) is exhibited by the polymer with the (CN)₂N^? anion.