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排序方式: 共有84条查询结果,搜索用时 15 毫秒
1.
C. V. Yelamaggad Manoj Mathews Uma Hiremath Geetha Nair D. S. Shankar Rao S. Krishna Prasad 《Liquid crystals》2003,30(8):899-908
A series of symmetrical dimers consisting of salicylaldimine moieties connected by flexible alkylene central spacer via ether linkages has been synthesized. In order to validate the empirical rule suggested by Date et al. to account for the smectic behaviour of such dimers, the chain length of the terminal alkoxy chain has been kept constant (C8) while the number of methylene units in the central spacer was varied from C3 to C11. Another aim of the present investigation was to understand structure-property relationship in these dimers in which the salicylaldimine mesogenic segment has been used for the first time in dimers. The mesomorphic behaviour of these dimers was evaluated using optical microscopy and differential scanning calorimetry and the structure of some of the mesophases has been further investigated with the help of X-ray diffraction. Our studies reveal that the dimers consisting of 3 to 8 methylene units in the flexible spacer show only smectic (smectic C and smectic A) phases. For the dimers containing 4, 6 and 8 methylene units in the central spacer, a unique filament growth pattern has been observed in the smectic A phase while cooling from the isotropic phase. The dimers containing of C9 to C11 methylene groups exhibit the nematic phase in addition to smectic modifications. This observation indicates that when the terminal chains are shorter than the spacer, the tendency to form smectic phases is not fully extinguished but is perhaps reduced. 相似文献
2.
Dielectric studies have been performed at elevated pressures on two compounds of a homologous series possessing a strongly polar terminal group and three phenyl rings in their molecular structure. This is the first high pressure dielectric study on such systems that exhibit a monolayer smectic A phase. Also notable is the fact that these compounds show a dual frequency response, a promising feature for fast liquid crystal display devices. The low frequency relaxation recorded in the nematic and smectic A phases is attributed to the reorientation of the molecules about the short axis. The temperature and pressure dependence of the relaxation frequency of this mode as well as the involved activation parameters are discussed. At a given relative temperature the relaxation frequency decreases as the pressure is increased. However, the parameter that characterizes the temperature dependences of the relaxation frequency, viz., the activation enthalpy, has a very weak dependence on pressure. In contrast, the activation volume shows a linear decrease with temperature. 相似文献
3.
T. S. Kiran D. C. Hiremath S. T. Nandibewoor 《Russian Journal of Physical Chemistry A, Focus on Chemistry》2007,81(12):2070-2077
The kinetics of oxidation of L-lysine by diperiodatocuprate (III) (DPC) in alkaline medium at a constant ionic strength of
0.15 mol/dm3 was studied spectrophotometrically. The reaction between DPC and L-lysine in an alkaline medium had a 1: 2 stoichiometry
(L-lysine: DPC). The reaction was first order in [DPC] and less than first order in [L-lysine] and [alkali]. The addition
of periodate had no effect on the rate of the reaction. The intervention of free radicals was observed in the reaction. The
oxidation reaction in alkaline medium was shown to proceed via a DPC-L-lysine complex. The main products were identified by
spot test and spectral studies. The reaction constants involved in different steps of the mechanism were calculated. The activation
parameters with respect to the slow step of the mechanism were computed and discussed, and thermodynamic values were also
determined.
The article is published in the original. 相似文献
4.
Hiremath Siddalingaiah A. Dodamani Ashok F. Naik Sunil G. 《Transition Metal Chemistry》2002,27(1):47-51
The title complex was prepared and characterized by elemental and spectral analyses. The formation constants of various heterocyclic nitrogen base adducts with the NiII–di(2,4-dibromophenyl)carbazonate have been determined in a monophase by spectrophotometry at 25 ± 0.1 °C. The monodenatate and bidentate bases form penta- and hexa-coordinated adducts respectively with 1:1 stoichiometry for the metal chelate-base, whereas the unsaturated monodentate bases form hexa-coordinated adducts with 1:2 stoichiometry. The behaviour of saturated heterocyclic bases such as pyrrolidine, piperidine, hexamethyleneimine and morpholine towards the metal chelate has been studied, and the results are discussed in terms of steric hindrance, basicity and ring structure. 相似文献
5.
S. Krishna Prasad Yoji Maeda Corresponding author D. S. Shankar Rao S. Anitha Nagamani Uma S. Hiremath C. V. Yelamaggad 《Liquid crystals》2013,40(11):1277-1283
The phase behaviour of two achiral bent core banana-shaped compounds, the hexyloxy (compound I) and decyloxy (compound II) members of the 1,3-phenylene bis[N-(2-hydroxy-4-n-alkoxybenzylidene)-4′-aminobenzoate] series was investigated under hydrostatic pressures up to 300?MPa using high pressure differential thermal analysis and light transmission methods. The reversible transition sequence crystal (Cr1)–B1 phase–isotropic liquid (I), observed at room pressure for compound I, remains in the pressure region up to c 70?MPa. At higher pressures a pressure-induced crystalline phase (Cri) appears between the Cr1 and B1 phases, its temperature region becoming wider with increasing pressure. The temperature vs. pressure phase diagram shows a triple point of 72.9?MPa and 160.3°C for the Cr1, Cri and B1 phases, indicating the lower limit of pressure for the Cri phase. In compound II the reversible transition sequence crystal (Cr1)–B2 phase–I is seen over the whole pressure region, and the temperature range of the B2 phase remains unaltered. It is concluded that both the B1 and B2 banana phases are stable over the whole pressure region studied. 相似文献
6.
Veeresh Tegginamath Chanabasayya V. Hiremath Sharanappa T. Nandibewoor 《Journal of Physical Organic Chemistry》2007,20(1):55-64
The oxidation of allyl alcohol by diperiodatoargentate(III) (DPA) is carried out both in the absence and presence of ruthenium(III) catalyst in alkaline medium at 298 K and a constant ionic strength of 1.1 mol dm?3 was studied spectrophotometrically. The oxidation products in both the cases were acrolein and Ag(I), identified by spectral studies. The stoichiometry is same in both the cases, that is, [AA]/[DPA] = 1:1. The reaction shows first order in [DPA] and has less than unit order dependence each in both [AA] and [Alkali] and retarding effect of [IO] in both the catalysed and uncatalysed cases. The order in [Ru(III)] is unity. The active species of DPA is understood to be as monoperiodatoargentate(III) (MPA) in both the cases. The uncatalysed reaction in alkaline medium has been shown to proceed via a MPA–allyl alcohol complex, which decomposes in a rate determining step to give the products. In catalysed reaction, it has been shown to proceed via a Ru(III)‐allyl alcohol complex, which further reacts with one molecule of MPA in a rate determining step to give the products. The reaction constants involved in the different steps of the mechanisms were calculated for both reactions. The catalytic constant (Kc) was also calculated for catalysed reaction at different temperatures. The activation parameters with respect to slow step of the mechanisms were computed and discussed for both the cases. The thermodynamic quantities were also determined for both reactions. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
7.
The Vilsmeier-Haack formylation reaction and several additional reactions have been employed to prepare a variety of benz[e]- and benz[g] indole-2- and 3-carboxaldehydes. Similar conditions have been utilized to prepare several 2,3-disubstituted benz[g] indole-5-carboxaldehydes. 相似文献
8.
Nandibewoor Sharanappa T. Hiremath Gouri A. Timmanagoudar Prakash L. 《Transition Metal Chemistry》2000,25(4):394-399
The oxidation of thiocyanate by periodate has been studied in alkaline media. A micro quantity of RuIII is sufficient to catalyse the reaction. The active catalytic species and oxidant in the reaction are understood to be [Ru(H2O)5OH]2+ and IO−
4. The autocatalysis exhibited by one of the products, cyanate, is attributed to adduct formation between cyanate and periodate.
A composite mechanism and rate law are proposed. The reaction constants involved in the mechanism are evaluated.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
9.
The Rate-Controlled Constrained-Equilibrium (RCCE) method is a thermodynamic based dimension reduction method which enables representation of chemistry involving n s species in terms of fewer n r constraints. Here we focus on the application of the RCCE method to Lagrangian particle probability density function based computations. In these computations, at every reaction fractional step, given the initial particle composition (represented using RCCE), we need to compute the reaction mapping, i.e. the particle composition at the end of the time step. In this work we study three different implementations of RCCE for computing this reaction mapping, and compare their relative accuracy and efficiency. These implementations include: (1) RCCE/TIFS (Trajectory In Full Space): this involves solving a system of n s rate-equations for all the species in the full composition space to obtain the reaction mapping. The other two implementations obtain the reaction mapping by solving a reduced system of n r rate-equations obtained by projecting the n s rate-equations for species evaluated in the full space onto the constrained subspace. These implementations include (2) RCCE: this is the classical implementation of RCCE which uses a direct projection of the rate-equations for species onto the constrained subspace; and (3) RCCE/RAMP (Reaction-mixing Attracting Manifold Projector): this is a new implementation introduced here which uses an alternative projector obtained using the RAMP approach. We test these three implementations of RCCE for methane/air premixed combustion in the partially-stirred reactor with chemistry represented using the n s=31 species GRI-Mech 1.2 mechanism with n r=13 to 19 constraints. We show that: (a) the classical RCCE implementation involves an inaccurate projector which yields large errors (over 50%) in the reaction mapping; (b) both RCCE/RAMP and RCCE/TIFS approaches yield significantly lower errors (less than 2%); and (c) overall the RCCE/TIFS approach is the most accurate, efficient (by orders of magnitude) and robust implementation. 相似文献
10.
Hiremath RK Rabinal MK Mulimani BG Khazi IM 《Langmuir : the ACS journal of surfaces and colloids》2008,24(19):11300-11306
Silicon surface was chemically modified by covalent attachment of homologous organic molecules having different dipole moments. Surface photovoltage measurements clearly confirm that organic molecules have a profound effect on surface band bending of semiconductor. Metal-molecules--silicon junctions were constituted for molecules belonging to ethynylbenzene series using soft mercury contact. These junctions show a systematic change in the electrical charge transport with dipole moment of molecules. Parameters such as ideality factor, barrier height, and density of interface states of various junctions are estimated to understand the role of organic molecules. These studies offer the prospect to develop molecular electronics, which may find potential applications in solar cells and chemical and biological sensors. 相似文献