Máximo Barón

Definitions of basic terms relating to low-molar-mass and polymer liquid crystals (IUPAC Recommendations 2001)

This document is the first published by the IUPAC Commission on Macromolecular Nomenclature dealing specifically with liquid crystals. Because of the breadth of its scope, it has been prepared in collaboration with representatives of the International Liquid Crystal Society. The document gives definitions of terms related to low-molar-mass and polymer liquid crystals. It relies on basic definitions of terms that are widely used in the field of liquid crystals and in polymer science. The terms are arranged in five sections dealing with general definitions of liquid-crystalline and mesomorphic states of matter, types of mesophases, optical textures and defects of liquid crystals, the physical characteristics of liquid crystals (including electro-optical and magneto-optical properties), and finally liquid-crystal polymers. The terms that have been selected are those most commonly encountered in the conventional structural, thermal, and electro-optical characterization of liquid-crystalline materials.

DEFINITIONS OF TERMS RELATING TO REACTIONS OF POLYMERS AND TO FUNCTIONAL POLYMERIC MATERIALS (IUPAC Recommendations 2003)

The document defines the terms most commonly encountered in the field of polymer reactions and functional polymers. The scope has been limited to terms that are specific to polymer systems. The document is organized into three sections. The first defines the terms relating to reactions of polymers. Names of individual chemical reactions are omitted from the document, even in cases where the reactions are important in the field of polymer reactions. The second section defines the terms relating to polymer reactants and reactive polymeric materials. The third section defines the terms describing functional polymeric materials.

Unexpected chirality in trans-1,4-dicyanocyclohexane

Abstract The experimental non-zero dipole moment of trans -1,4-dicyanocyclohexane was verified through a procedure little sensitive to solute/solvent interactions. This value cannot be explained on the basis of the generally accepted centrosymmetry for trans -1,4-derivatives of cyclohexane. NMR data of both this compound and its C-1, C-4 di-deuteroderivative, as well as semi-empirical theoretical calculations with the MNDO methods show that besides a centro-symmetric form there are also low energy stable non-centrosymmetric geometries. The latter exist as a helical deformation that can account for the non-zero value of the experimental dipole moment.

Conformational studies of trans-1,4-substituted cyclohexanes. I: Trans-1,4-cyclohexanedicarbonitrile

The molecules of the title compound (C 8 H 10 N 2 ), which each adopt a chair conformation with the CN substituents equatorially bonded, lie on crystallograpbic inversion centres and are linked by CN...CN intermolecular interactions to form (101) sheets. The sheets are additionally stabilized by short C-H...N contacts

Temperature control in small air‐heated measuring cells

Temperature control in a liquid sample contained in a Chatelain prism was achieved in a closed chamber through warm air circulation. A proportional electronic thermostat and two very small and thin thermistors allowed a control within ±0.1 °C.

Dielectric properties of binary systems 8. Improved model for alcohol/non polar systems.

Abstract The dielectric behavior of polar non polar liquid systems is treated as the result of associations through changes in the model proposed by Mechetti and Baron for very dilute solutions. The existence of a 1:1 interaction product (or complex) is assumed and the equilibrium constant (K) of complex formation is introduced. As a result the range of validity of the model extends into the non-dilute region and up to the limit where complexes other than 1:1 appear. These changes allow also to calculate the equilibrium constant (K) for the 1:1 complex from dielectric measurements in the dilute region. The values are in good agreement with those found in the literature.

Ab Initio and in-Crystal Geometry of trans-1,4-Dibromo1,4-dicarboxymethylcyclohexane

The structure of trans-1,4-dibromo-1,4-dicarboxymethylcyclohexane (I) has been determined by single crystal x-ray diffraction. The molecules, located on symmetry centers, are in the rigid chair conformation with the Br and COOCH3 axial and equatorial, respectively. The molecular geometry observed in the crystal is similar to that calculated for the isolated molecule using ab initio calculations performed at the HF/6-31(d) level. A peculiar arrangement of the carboxymethyl substituents, along with short contacts involving the Br atoms, seem to play a role in the stabilization of the crystalline structure.

Conformational Studies of trans-1,4-Substituted Cyclohexanes. II. trans-1,4-Dibromo-1,4-cyclohexanedicarbonitrile, C8H8Br2N2

The molecule of the title compound, which has crystallographic symmetry 2/m, has a chair conformation with the Br and CN substituents located equatorially and axially, respectively. Crystal packing analysis shows that the molecules are organized, via CN...CN dipolar interactions, in layers parallel to (001). The layers are linked by CBr...CBr and C-H...Br interactions

Liquid crystal birefringence and electric dipole moment relationship with temperature, weak magnetic field and molecular geometry.

Abstract Birefringence in the mesophase of 4-cyano-4′-n-pentylbiphenyl (5CB) was measured directly under a magnetic field (1200 and 2000 gauss) as a function of temperature with field parallel and perpendicular to the optical axis. Electrical dinole moments of 5CB and benzonitrile were calculated with the Mechetti-Baron equations from measurements at three temperatures. Molecular geometries were examined with a semiempirical procedure (AMPAC). The results suqgest that thermal stirring and internal rotations appear to overcome orientational effects of the applied field.

Structure of some optically active chloralides

Abstract The conformation of two chloralides derived from S(+)lactic acid and one each of S(−)- and R(+)malic acid have been established through dipole moment measurements and NMR spectra.