CPS L 946

A thermodynamic inequality, providing the possibility of calculating the limiting number of adsorbed layers from the excess adsorption data, is discussed. For identical cross-sectional areas of molecules of both components this inequality simplifies considerably and defines the limiting value of the surface phase capacity. Therefore, it may be used as criterion of the accuracy of the surface phase capacity value evaluated by other methods. Taking this criterion into account a method is proposed to determine the surface phase capacity and number of adsorbed layers from the excess adsorption data. It is verified by using the excess adsorption data available from the literature.     

Steric and electronic contributions to barriers of internal rotation in 1,8-dibenzoylnaphthalenes

Restricted rotation about the naphthalenylcarbonyl bonds in the title compounds resulted in mixtures of cis and trans rotamers, the equilibrium and the rotational barriers depending on the substituents. For 2,7-dimethyl-1,8-di-(p-toluoyl)-naphthalene (1) ΔH° = 3.66 ± 0.14 kJ mol^?1, ΔS° = 1.67 ± 0.63 J mol^?1 K^?1, ΔH^≠_ct = 55.5 ± 1.3 kJ mol^?1, ΔH^≠_ct = 51.9 ± 1.3 kJ mol^?1, ΔS^≠_ct = ?41.3±4.1 J mol^?1 K^?1 and ΔS^≠_ct = ?42.9±4.1 J mol^?1 K^?1. The rotation about the phenylcarbonyl bond requires ΔH^≠ = ?56.9±4.4 kJ mol^?1 and ΔS^≠ = ?20.5±15.3 J mol^?1 K^?1 for the cis rotamer, and ΔH^≠ = 43.5Δ0.4 kJ mol^?1 and ΔS^≠ =± ?22.4Δ1.3 J mol^?1 K^?1 for the trans rotamer. The role of electronic factors is likely to be virtually the same for both these rotamers but steric interaction between the two phenyl rings occurs in the cis rotamer only. Hence, the difference of the activation enthalpies obtained for the cis and trans rotamers, ΔΔH^?1 = 13.4 kJ mol^?1, provides a basis for the estimation of the role of steric factors in this rotation. For the tetracarboxylic acid 2 and its tetramethyl ester 3 the equilibrium is even more shifted towards the trans form because of enhanced steric and electrostatic interactions between the substituents in the cis form. The barriers for the rotation around the phenylcarbonyl bond and the cis-trans isomerization are lowered; an explanation for this result is presented.     

Umamidierungsreaktionen an offenkettigen Amino-amid-Systemen. 1. Mitteilung über Umamidierungsreaktionen

Transamidation Reaction of Open Chaine Amino-amides Amino-amides of type 11 with a primary amino and a N, N-disubstituted amide group isomerize under base catalysis completely to amino-amides 16 with a secondary amino and a N-monosubstituted amide group (see Scheme 3). Amino-amides having a secondary instead of the primary amino group are under base catalysis in equilibrium with the corresponding isomeres (Scheme 4). The opening of the proposed tetrahedral intermediate 13 (Scheme 3) takes place under stereo-electronic control (Schemes 5 and 6).     

Nematic liquid crystals exhibiting high birefringence

Two fluorinated isothiocyanato nematic liquid crystalline compounds, 4′-butylcyclohexyl-3, 5-difluoro-4-isothiocyanatobiphenyl and 4′-pentylcyclohexyl-3, 5-difluoro-4-isothiocynatobiphenyl are studied in detail to obtain their different physical parameters. Optical polarizing microscopy, differential scanning calorimetry, density and dielectric studies have been carried out for the two samples. Both the samples were found to have high clearing temperature (>100 °C) and exhibit small enthalpy of transition. The two samples exhibit high optical birefringence (Δn > 0.2). The values of order parameters for the two samples were obtained using different approaches, namely, Vuks’, Neugebauer’s, modified Vuks’ and direct extrapolation method from birefringence data. Experimentally obtained values of order parameters have also been compared with theoretical Maier–Saupe values. The parallel and perpendicular components of dielectric permittivity values of the two compounds were also calculated and their anisotropy values were found to be small. The effect of temperature on the molecular dipole moment μ and the angle of inclination β of the dipole axis with the director have also been investigated in this work.     

Design and application of a gas chromatograph-gas chromatograph transfer line

A simple innovation is proposed in this work: to use interface (transfer line, TL), which allows quantitative mass transfer between two gas chromatographs. This approach assumes that one chromatograph serves as a conventional GC apparatus and the second one only as a thermostat with the appropriate detector(s) mounted. Two possible applications of the TL were tested: an "inlet-TL-detector" system and a system for dual-detection analysis, i.e. mass spectrometry and atomic emission detection. Results obtained for both of the systems show that the interface enables effective connection of two independent chromatographs. The transfer line is a manufacturer-independent innovation (with its own electronics), easy to set up and maintain.     

Dielectric investigation of the diamagnetic anisotropy and elasticity of 4-trans-4′-n-hexyl-cyclohexyl-isothiocyanatobenzene (6CHBT)

Abstract

We have measured the dielectric constants of 6CHBT. The results from studies of various alignments and thicknesses measured under different electric and magnetic fields are presented. We discuss how the dielectric properties depend on boundary conditions, sample thickness and the magnitudes of electric and magnetic fields. Experimental results and discussion in the terms of continuum theory make it possible to compute the diamagnetic anisotropy (Δχ), as well as the splay and bend elastic constants (K ₁₁, K ₃₃) of 6CHBT.     

3-Aryl- or 3-(trans-4-alkylcyclohexyl)- 6-arylcyclohex-2-enones: synthesis,transformations and mesomorphic properties

The synthesis and chemical transformations of 3-aryl- or 3-(trans-4-alkylcyclohexyl)- 6-arylcyclohex-2-enones into liquid crystalline compounds are discussed. These 3,6-disubstituted cyclohex-2-enones were prepared by the condensation of appropriate Mannich salts or trans-4-alkylcyclohexyl 2-bromoethyl ketones with 4-substituted benzyl methyl ketones.     

Three ring dioxanes as dopants enhancing the stability of the smectic C phase

Abstract

Searching for compounds which could be useful as modifiers of smectic C mixtures, we have synthesized four homologous series of three ring dioxanes, 2BBD, 5BBD, 2CBD, and 5CBD. Their phase transition temperatures and enthalpies were measured and their liquid crystal phases identified. Compounds belonging to series n-BBD form smectic B_cr phases for shorter alkyl chains, and smectic B_cr and A phases, for longer chains. Compounds belonging to the n-CBD series exhibit the smectic A phase, but those with longer alkyl chains have exclusively smectic B phases and those with short tails have other low temperature, highly ordered smectic phases. The compounds were added to smectic C mixture and it was found that some can be useful as dopants. Compounds with longer alkyl tails in the molecule are more suitable for this purpose; the type of ring in the core is less important.