New synthesis of substituted pyrazines

Conclusions A new synthesis of substituted pyrazines was accomplished by the reaction of aldehydes with aminoacetone hydrochloride in refluxing alcohol.Translated from Izvestiya Alademii Nauk SSSR, Seriya Khimicheskaya, No. 3, pp. 707–708, March, 1973.     

A dipole-moment study of substituted pyrazines and quinoxalines

An attempt has been made to rationalize the dipole moments of 2-chloro-, 2-ethoxy-, 2-ethylthio-, 2-amino-, 2-ethylamino- and 2-diethylamino-pyrazine in terms of substituentring mesomeric effect. In 2-substituted pyrazines, the substituent mainly interacts with the ortho-to-substituent ring-nitrogen atom. Preferred conformations are proposed for 2-ethoxypyrazine and 2-methoxypyridine, 2-ethylthiopyrazine and 2-methylthiopyridine, 2,5-diethoxypyrazine, 2,3-dimethoxyquinoxaline and 2,3-bis(methylthio)quinoxaline. The dipole moments of aminopyridines, amino-s-triazine and methoxy-s-triazine are also interpreted.     

Redox indicator properties of some substituted chrysoidins

Indicator properties of eleven substituted chrysoidins have been studied. Conditional reduction potentials of the three appreciably reversible indicators in this group were obtained by classical approaches and by use of a potentiopoised standard solution procedure. Chemical and electrochemical observations lead to the conclusion that the other eight indicators act irreversibly in their oxidation. Hence, only transition potential ranges can be reported for these. Substitution in other than the 4-position induces greater irreversibility, while the hydroxy group in the 4-position produces a greater degree of reversibility than does either the methoxy or ethoxy group, 4-Hydroxychrysoidin appears to be the best of the group for bromate titrations.     

Liquid crystal alignment properties of n-alkylsulphonylmethyl-substituted polyoxyethylenes

The liquid crystal (LC) alignment properties of LC cells fabricated with films of n-alkylsulphonylmethyl-substituted polyoxyethylenes (#S-PEO, #?=?4, 6, 7, 8 and 10), where # is the number of carbon atoms in the n-alkyl side groups having different n-alkyl chain length, were investigated as a function of the rubbing density. The LC cells made from unrubbed #S-PEO (# ≥8) films having more than eight carbon atoms in the n-alkyl side groups showed homeotropic LC alignment. The homeotropic LC alignment behaviour correlated well with the surface energy values of the unrubbed #S-PEO films; homeotropic LC alignment was observed when the surface energy values of the unrubbed #S-PEO films were smaller than about 21.62 mJ m^?2. The LC cells made from rubbed #S-PEO (# ≥7) films having more than seven carbon atoms with a rubbing density of 150 showed homeotropic LC alignment. It was also found that the tilt angle of the LCs on the rubbed #S-PEO films was affected not only by the n-alkyl chain length of the polymers, but also by the rubbing density, regardless of the surface energy value of the #S-PEO film.     

Synthesis and some properties of substituted 4-azafluorenes

Some chemical properties — the oxidation, condensation with aromatic aldehydes, bromination, dimerization, and amination — of 4-azafluorenes derived from -methylene-1,5-diketones are studied.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 7, pp. 950–953, July, 1990.     

A novel and versatile entry to asymmetrically substituted pyrazines

A novel and convenient procedure for the synthesis of asymmetrically tri- and tetrasubstituted pyrazines starting from para-methoxybenzyl-protected 3,5-dichloro-2(1H)-pyrazinones was elaborated. The key step is the conversion of the intermediate para-methoxybenzyl-protected thiopyrazinone upon treatment with MeI/I(2), into a pyrazine, rendering the chlorine in the C5-position susceptible to substitution. This approach entails the orthogonal introduction of the four substituents of the pyrazine scaffold. The application of microwave irradiation during different steps of the sequence has been shown to be highly valuable for speeding up reactions.     

Liquid crystal alignment properties of 2-naphthoxymethyl-substituted polystyrenes

The liquid crystal (LC) alignment properties of LC cells fabricated with films of 2-naphthoxymethyl-substituted polystyrenes with different contents of naphthoxymethyl side groups were investigated. The polymer films exhibited good optical transparency in the visible light region (400–700 nm). The LC cells made from the unrubbed films of polymers having more than 57 mol%?of 2-naphthoxymethyl containing monomeric units showed homeotropic LC alignment with a high pretilt angle of about 90^o. Good electro-optical characteristics, such as the threshold voltage, response time, voltage holding ratio and residual DC voltage were observed for the LC cells fabricated with the polymer having 100 mol%?of 2-naphthoxymethyl containing monomeric units as an LC alignment layer.     

Synthesis and properties of some laterally substituted liquid crystals

This paper presents a number of laterally substituted liquid crystalline compounds which have been synthesized by systematically varying both the position and the type of the lateral substituent. The influences of such structural changes on the physico-chemical properties of new compounds are discussed and compared with those of the corresponding laterally unsubstituted analogues.     

Liquid crystal properties of a self-assembling viral coat protein

Monomers of the fd bacteriophage major coat protein, g8p, interact to form a helical bent-core structure surrounding the viral deoxyribonucleic acid (DNA). It was hypothesised that g8p has mesophasic characteristics guiding viral coat assembly. Atomic force and scanning electron microscopy reveal that g8p monomers organise to form films that wrap around a central axis to form birefringent fibres. These fibres resemble the filament structure of bent-core thermotropic B7 liquid crystals. These results offer insight into the g8p self-assembly mechanism that results in the formation of new viral particles in vivo.     

Synthesis,structure, and biological properties of N-oxides of some 2-substituted quinoxalines and pyrazines

2-Methoxy- and 2-hydroxy-substituted quinoxaline and pyrazine N,N-dioxides and N-oxides of a number of quinoxaline-2-carboxylic acid derivatives were synthesized in order to study their biological activity. It is shown that the N-monoxides and N,N-dioxides of 2-hydroxy derivatives of quinoxaline exist primarily in the oxo form. Strong intramolecular hydrogen bonds were detected in the case of 1-N-oxides of 2-hydroxy and 2-carboxamido derivatives of quinoxaline. Substances with antibacterial and antituberculous activity were found among the synthesized compounds.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 2, pp. 278–283, February, 1976.     

A comparison of some pyridyl-substituted pyrazines as analytical reagents

A comparative study of six 2-pyridyl and 2-(6-methyl-pyridyl) derivatives of pyrazine as chromogenic reagents of the ferroin and cuproin types has established 2,3,5,6-tetrakis(2'-pyridyl)pyrazine as a highly sensitive reagent for iron(II); 2,3-bis(2'-pyridyl)-5,6-dihydropyrazine and 2,3-bis[2'-(6'-methyl pyridyl)]-5,6-dihydropyazine both show high sensitivity and characteristic high selectivity in their reactions with iron(II) and copper(I) respectively-the reaction with copper(I) being almost as sensitive as that given by bathocuproine. The ease with which the highly coloured metal chelates can be extracted into immiscible solvents to give stable solutions makes these reagents useful for the determination of traces of iron and copper.     

Chiroptical properties and conformation of some 2-alkyl substituted dicarboxylic acids

CD spectra in EPA (a mixture of ethanol, isopentane and diethyl ether) at 25° and -185° were measured for the following acids and their methyl esters: (R)-2-methyl-, (R)-2-ethyl-, (R)-2-n-propyl-, (R)-2-n-butyl-, (R)-2-n-hexyl-, (R)-2-isobutyl-, (S)-2-isopropyl- and (S)-2-cyclohexylsuccinic acids, (R)-2-methylglutaric acid, (R)-2-methylsuberic acid, (R,R)-2,3-dimethyl-succinic acid and (+)-trans-Caronic acid (3,3-dimethyl-1,2-cyclopropane-dicarboxylic acid). The CD data are explained in terms of the conformation around the C₁C₂, C₂C₃ and C₃C₄ bonds.     

Electronic band structures and electronic properties of some substituted linear polyenes

A series of linear polyenes having the side groups, Cl, Me, CN, Ph, and —PhOMe, has been studied by a self-consistent LCAO tight-binding method. It is found that, with normal bond lengths, several of these materials are predicted to be electronic conductors in the solid state. This property is lost, however, when the lattice vector is increased. Of particular interest are the phenyl- and phenoxy-substituted compounds where the rings form conducting paths by transannular overlap. Energy transfer and the effects of disorder and segmental rotation of the backbone are also considered.     

Liquid crystal properties of new ionic liquid crystal compounds having a 1,3-dioxane ring

New pyridinium type chiral ionic liquid crystal materials having a 1,3-dioxane ring in the central core, (+)- N -2-methylbutyl-4-(5-alkyl-1,3-dioxan-2-yl)pyridinium bromides (6), were synthesized. Mixture A was made by adding 5.9 wt % of compound 6?3 to the ferroelectric liquid crystal mixture Merck 4655-100; its phase transitions and some liquid crystal properties were measured. In spite of a large decrease of P_s for mixture A, its response time A was the same as that of Merck 4655-100. The dielectric constants perpendicular to the molecular axis for the smectic C* and smectic A phases were measured for the mixture and Merck 4655?100: in the smectic C phase, these dielectric constants were almost the same (4.5～5.5), but in the smectic A phase, the perpendicular dielectric constant of the mixture was 47.0 and that of Merck 4655?100 was 4.5.     

Liquid crystalline and dielectric properties of homologous series of substituted 1,3,4-oxadiazoles

Three homologous series of 2-alkylthio-5-phenyl-1,3,4-oxadiazole derivatives were synthesized [1, 2] and their liquid crystalline and dielectric properties investigated. Depending on the chain length, nematic, smectic A and smectic C phases were observed [1] . Dielectric investigations indicate a cross over of epsilon o and epsilon o at the N/SmA phase transition. This is explained by a transition from a more statistical into an antiparallel correlation of the dipoles, mainly caused by steric effects.     

Liquid crystal properties of new ionic liquid crystal compounds having a 1,3-dioxane ring

New pyridinium type chiral ionic liquid crystal materials having a 1,3-dioxane ring in the central core, (+)- N -2-methylbutyl-4-(5-alkyl-1,3-dioxan-2-yl)pyridinium bromides ( 6 ), were synthesized. Mixture A was made by adding 5.9 wt % of compound 6-3 to the ferroelectric liquid crystal mixture Merck 4655-100; its phase transitions and some liquid crystal properties were measured. In spite of a large decrease of P s for mixture A, its response time A was the same as that of Merck 4655-100. The dielectric constants perpendicular to the molecular axis for the smectic C* and smectic A phases were measured for the mixture and Merck 4655-100: in the smectic C phase, these dielectric constants were almost the same (4.5~5.5), but in the smectic A phase, the perpendicular dielectric constant of the mixture was 47.0 and that of Merck 4655-100 was 4.5.