X-Ray Investigation of Chiral β-Hydroxyketone Derived From (+)-Isomenthone

X-ray analysis was carried out to study the molecular structure of β-hydroxyketone, which is one of the minor products of selective aldol condensation of (−)-menthone with 4-carbomethoxybenzaldehyde. The cyclohexanone ring of the compound has a practically undistorted chair conformation with an axial orientation of the 1-methyl group and the bulkiest 2-[1′-hydroxy-1′ -(4-carbomethoxyphenyl)]methyl substituent and the equatorial orientation of the isopropyl group in the 4 position. The stereochemical configuration was found to be (1R,2R,4 R, 1′ S), supporting that the compound belongs to the group of (+)-isomenthones; i.e., the starting (-)-menthone undergoes (to a certain extent) epimerization under the reaction conditions used. In crystal, there is intermolecular hydrogen bonding >C=O...HO- (the -O...H- bond length is 2.15 Å). The molecular conformation in hydroxyketone crystals differs from the one which prevails in solutions (according to previous NMR data) and which is characterized by an inverted cyclohexanone ring and intramolecular hydrogen bonding >C=O...HO.Original Russian Text Copyright © 2004 by S. V. Shishkina, T. G. Drushlyak, L. A. Kutulya, N. S. Pivnenko, and O. V. Shishkin__________Translated from Zhurnal Strukturnoi Khimii, Vol. 45, No. 5, pp. 933–940, September–October, 2004.     

New (1R,4R)-2-arylidene-p-menthan-3-ones with a bridging ester group in the arylidene fragment. Synthesis and behavior in liquid-crystalline systems

(1R,4R)-2-(4-Hydroxybenzylidene)- and (1R,4R)-2-(4"-hydroxybiphenyl-4-yl)methylene-p-menthan-3-ones were synthesized by condensation of (–)-menthone with O-tetrahydropyran-2-yl derivatives of 4-hydroxybenzaldehyde and 4"-hydroxy-4-formylbiphenyl, respectively, in a DMSO—base medium followed by the removal of the protective group. The reactions of these hydroxy derivatives with 4-alkylbenzoic, 4-alkyloxybenzoic, trans-4-alkylcyclohexane-4-carboxylic, and 4"-alkylbiphenyl-4-carboxylic acids afforded three series of new chiral esters. Compounds containing the arylidene moiety with three benzene rings were found to exhibit liquid-crystalline properties. The characteristic features of these compounds are discussed based on the results of studies by polarizing microscopy, differential scanning calorimetry, and small-angle X-ray scattering. It was found that the mesomorphic compounds under study can form a smectic A mesophase, twist grain boundary mesophases (TGBA), and blue phases in a wide temperature range. Upon dissolution of certain of chiral compounds in 4"-cyano-4-pentylbiphenyl, a rather high twisting power and the thermal stabilizing effect on mesophases were observed.     

Proton Magnetic Resonance and Molecular Simulation in Configurational and Conformational Analysis of Cyclohexanone Derivatives

Developing the previously tested approach to the configurational and conformational analysis of cyclic chiral compounds based on a complex use of NMR spectra and molecular simulation, we determined the configuration 1R, 2R, 4R, 1S and conformational state of 2[1hydroxy1(4carbomethoxyphenyl) methyl]pmenthane3one, a minor product of the directed aldol reaction of (–)menthone with 4carbomethoxybenzaldehyde. The configurations of the cyclic chiral centers were determined by analysis of the spin–spin coupling constants of the protons of the cyclohexanone ring for the most probable conformations of alternative stereoisomers. The S configuration of the C (1) exocyclic chiral center was established from the different orientation of the benzene ring relative to the cyclohexanone fragment in alternative stereoisomers, as shown by semiempirical quantumchemical simulations (AM1 and PM3 methods), and from the observed difference in proton chemical shift between the examined hydroxyketone and the model (+)isomenthone (1R, 4Rdiastereomer).     

High-birefringence nematic liquid crystal for broadband THz applications

Liquid crystals (LCs) have been studied extensively in the visible range for their dielectric tunability, and the characterisation in the terahertz (THz) range has gained increasing interest due to the need for active THz modulation and switching devices. In this paper, we use THz time-domain spectroscopy to measure the frequency-dependent birefringence and the absorption coefficient of a number of commercial and non-commercial nematic LCs, including E7, BL037, MDA-98-1602, LCMS-107, GT3-23001 and 1825, over a range of bias voltages at room temperature. Furthermore, several basic components of LC mixture are analysed to establish their contributions to birefringence and theoretical model is used to fit the absorption spectra. The large tunability and low loss measured for a range of samples show that the LCs are useful tunable dielectrics for compact, efficient and broadband THz devices.     

Synthesis and spectral-luminescence properties of carbonyl derivatives of 2-(2-thienyl)-5-aryloxazoles

Electrophilic substitution reactions in the 2-(2-thienyl)-5-aryloxazole series and the spectral-luminescence properties of the compounds obtained were investigatedTranslated from Khimiya Geterotsiklicheskikh Soedinenii, No. 6, pp. 839–844, June, 1989.     

Chemical properties of 2,2,4-trisubstituted 2,3-dihydro-1H-1,5-benzodiazepines

Acetylation and nitrosation of 2,4-diaryl-2-methyl-2,3-dihydro-1H-1,5-benzodiazepines take place at the azomethyne nitrogen. Reduction is stereoselective.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 8, pp. 1122–1126, August, 1987     

Distinctive features of a pulsed beam scattering on a plane surface (two-dimensional case)

A two-dimensional problem of scattering of pulsed beams having arbitrary time and spatial form on a plane surface of a lossy dielectric halfspace is solved. A pulsed beam has been modeled by letting an E- or H-polarized plane pulse with homogeneous front pass through a space filter. The reflected pulse is found using an expansion of the incident pulsed beam over time-harmonic plane waves.     

Synthesis and spectral properties of 2-methyl-5-aryl-1,3,4-oxadiazoles

By heterocyclization of 1-acyl-2-aroylhydrazines under the influence of strong dehydrating substances, a series of 2-methyl-5-aryl-1,3,4-oxadiazoles has been synthesized and their UV, IR, and PMR spectra have been investigated. Through analysis of data on the influence of substituents on the position of the maximum in the electronic absorption spectrum, together with calculated data, it has been shown that the long-wave band of 2-methyl-5-phenyl-1,3,4-oxadiazole is due to an S₀–S₁ transition of the –^* type and that it is a charge transfer band for transfer from the phenyl radical to the oxadiazole ring; the 1,3,4-oxadiazole ring as a substituent has an electron-acceptor character.Institute of Single Crystals, National Academy of Sciences of the Ukraine, Khar'kov 310001. Khar'kov State University, Khar'kov 310077. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 6, pp. 816–821, June, 1997.     

Synthesis and tautomerism of 5,7-diaryl-4,7(6,7)-dihydrotetrazolo[1,5a]pyrimidines

5,7-Diaryl-4,7(6,7)-dihydrotetrazolo[1,5-a]pyrimidines were synthesized by the cyclocondensation of 5-aminotetrazole with chalcones. The tautomerism of the compounds obtained is discussed.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 11, pp. 1489–1493, November, 1988.