Low-temperature nematic phase in asymmetrical 1,3,4-oxadiazole bent-core liquid crystals possessing lateral methoxy group

Asymmetrical bent-core molecules based on 1,3,4-oxadiazole bent-core unit have been synthesised as a new design with a lateral methoxy group at outer phenyl ring of the molecule. These new asymmetrical bent-core molecules resemble hockey-stick shaped due to the presence of two different arms of different lengths. One arm of these molecules is elongated having two phenyl rings and possesses a 4-n-alkyloxy chain of a different number of carbon atoms (n = 4, 8, 12 and 18) and other arm is short and has one phenyl ring with fixed 4-n-octyloxy chain. The bent-core molecules possess a lateral polar methoxy group at the elongated arm of the molecule. These bent-core compounds exhibited fluorescence emission in the UV wavelength region (~377–386 nm) whereas in acetonitrile and dimethylformamide, solvent displays blue emission peak with a large stoke shift.The bent-core molecules with the number of carbon atoms (n = 4, 8 and 12) at the elongated arm exhibited monotropic nematic phase at low temperature, while the 4-n-octadecyloxy chain at the elongated arm displayed smectic A phase. Dielectric studies were performed in the nematic phase of the bent-core mesogens confirm the formation of the cybotactic cluster in the nematic mesophases.     

Aspherical‐Atom Modeling of Coordination Compounds by Single‐Crystal X‐ray Diffraction Allows the Correct Metal Atom To Be Identified

Single‐crystal X‐ray diffraction (XRD) is often considered the gold standard in analytical chemistry, as it allows element identification as well as determination of atom connectivity and the solid‐state structure of completely unknown samples. Element assignment is based on the number of electrons of an atom, so that a distinction of neighboring heavier elements in the periodic table by XRD is often difficult. A computationally efficient procedure for aspherical‐atom least‐squares refinement of conventional diffraction data of organometallic compounds is proposed. The iterative procedure is conceptually similar to Hirshfeld‐atom refinement (Acta Crystallogr. Sect. A­ 2008 , 64, 383–393; IUCrJ. 2014 , 1,61–79), but it relies on tabulated invariom scattering factors (Acta Crystallogr. Sect. B­ 2013 , 69, 91–104) and the Hansen/Coppens multipole model; disordered structures can be handled as well. Five linear‐coordinate 3d metal complexes, for which the wrong element is found if standard independent‐atom model scattering factors are relied upon, are studied, and it is shown that only aspherical‐atom scattering factors allow a reliable assignment. The influence of anomalous dispersion in identifying the correct element is investigated and discussed.     

Spin, iso-spin dependence of nucleon-nucleon effective interaction in nuclear matter calculations

A set of density dependent nucleon-nucleon (N-N) interactions has been examined in nuclear matter calculations by varying spin-isospin contributions. Two sets of potentials have been considered. One having a density dependentσ-function type short range part followed by one term long range Gaussian part while the other having a density dependentσ-function part followed by two Gaussian terms. The strength parameters of the potential have been fitted to the saturation properties of nuclear matter, i.e. binding energy per particle of 15.5 MeV atk _F=1.35 fm⁻¹. Several sets of these two potentials have been generated by varying the strength parameterM of Majorana exchange operatorP _M. It is seen thatM indirectly controls the spin, iso-spin contribution to the interaction potential and thus affects the nuclear matter properties such as compressibility and symmetry energy considerably, while variation of these quantities with the range parameterμ for givenM is moderate at lowM values while at higherM values it is quite large.     

Phototransformations of some 3‐cyclohexenyloxychromenones: Synthesis of Spirocyclic compounds

The phototransformation of the 3‐cyclohexenyloxychromenones by irradiation with a pyrex‐filtered light from a 125 W Hg vapor lamp under an inert atmosphere into the spirocyclic fused xanthenones was described. The efficacy of the protocol depended upon the position (o‐, m‐, or p‐) of the cyclohexenyloxy group appended to the 2‐aryl moiety on the chromenone nucleus, which was further invoked by steric, electronic, and proximity considerations. The structure(s) of the substrates and photoproducts were established using the spectroscopic (IR and NMR) data.     

Photoabsorption spectrum of small (n=2-6, 13) clusters

Theoretical studies of the photoabsorption spectra of clusters (n =2-6, 13) have been carried out using a linear combination of atomic orbitals molecular-orbital approach within a density functional scheme and a first-order perturbation approach. An analysis of the electronic states based on an angular-momentum decomposition around the center of mass of the cluster has been used to label the various transitions. It is shown that the spectra change significantly with size and are sensitive to the geometrical arrangement. They can be used to identify the isomers. Received: 2 June 1998 / Received in final form: 23 October 1998     

An efficient catalyst-free synthesis of novel benzo[a][1,3]oxazino[6,5-c]phenazine derivatives via one pot four-component domino protocol in water

A catalyst-free multicomponent reaction (MCR) capable of affording a wide range of novel benzo[a][1,3]oxazino[6,5-c]phenazine derivatives via one pot two-step domino protocol, in water is reported. Catalyst-free conditions along with green solvent system make the process ecofriendly as well as economical. Simple reaction conditions, easy work-up isolation, and purification of products are the significant advantages of the present protocol.     

Motion of a liquid-gas bubble mixture in the incipient cavitation stage

This article is concerned with the nonsteady motion of a mixture of an ideal incompressible liquid with gas bubbles in the incipient stage of cavitation. Solutions are obtained in the first and second approximations. The solutions are applied to pipe flow situations.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 5, pp. 151–153, September–October, 1976.The author is indebted to L. I. Sedov for valuable comments.     

Analysis of coupled conduction and radiation heat transfer in presence of participating medium- using a hybrid method

The current study addresses the mathematical modeling aspects of coupled conductive and radiative heat transfer in presence of absorbing, emitting and isotropic scattering gray medium within two-dimensional square enclosure. The walls of the enclosure are considered to be opaque, diffuse and gray. The enclosure comprised of isothermal vertical walls and insulated horizontal walls. A new hybrid method where the concepts of modified differential approximation employed by blending discrete ordinate method and spherical harmonics method, has been developed for modeling the radiative transport equation. The finite volume method has been adopted as the numerical technique. The effect of various influencing parameters i.e., radiation-conduction parameter, surface emissivity, single scattering albedo and optical thickness has been illustrated. The compatibility of the method with regard to solving coupled conduction and radiation has also been addressed.     

Motion of a liquid containing gas bubbles

In this paper a class of models of continuous media is constructed whose free energy depends on the density, the rate of change of density, and the temperature. Conditions at discontinuities in such models are found. A Kogarko model for a mixture of liquid with gas bubbles is obtained. Moreover, the propagation of small disturbances is investigated. In the third and fourth sections exact solutions are found for the problems of nonsteady and steady motion of a mixture of liquid and bubbles in a tube.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 6, pp. 111–116, November–December, 1971.The author thanks L. I. Sedov for guidance and valuable advice.