Vibrational spectra and structure of 4-cyano-4′-pentalkoxybiphenyl in different physical states

The polymorphism, conformation mobility and structure of 4-cyano-4′-pentalkoxybiphenyl (5OCB) in different physical states are studied by IR spectroscopy. The spectra were measured in the frequency range 400–4000 cm⁻¹ at temperatures from 300 to 350 K. The IR spectra of 5OCB are modeled using the concept of conformational mobility of these molecules. An analysis of the experimental and theoretical spectra reveals absorption bands whose spectroscopic parameters are sensitive to variations of temperature (experiment) and conformation (theory); a relationship between these changes is established. It is concluded that the polymorphism of 5OCB is of conformation type. In the solid crystalline state, 5OCB molecules have conformations with a planar biphenyl fragment; the angle of orientation of the plane of the carbon framework of the alkyl radical relative to the biphenyl fragment decreases as the temperature increases from 35° in the solid crystalline state to 10° in the liquid crystalline and isotropic liquid states. In both of these states the biphenyl fragment becomes nonplanar. The angle between the phenyl rings is up to 30°. Saratov State University. Institute of Physics, Ukrainian Academy of Sciences. Samarkand State University. Translated fromZhurnal Strukturnoi Khimii, Vol. 39, No. 1, pp. 55–60, January–February, 1998. This work was supported by RFFR grant No. 97-03-32175a.     

Tight‐binding molecular dynamics simulation of Si?H bond dissociation in silicon clusters

New model of Si? H bond dissociation is proposed and tested in the cluster Si₁₀H₁₆ by the simulation approach that combines classic molecular dynamics method and the self‐consistent tight‐binding electronic and total energy calculation one. It is shown that the monohydride Si? H bond is unstable with respect to silicon dangling bond and bend‐bridge Si? H? Si bond formation when this cluster traps the single positive charge and that hydrogen migrates through a path involving rather rotation around the Si? Si bond than the center of this bond (the bond‐centered position). These results can be useful for understanding hydrogen‐related phenomena at surfaces, interfaces, and internal voids of various hydrogenated silicon systems: electronic devices, silicon solar cells, and nanocrystalline and porous silicon. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem 93: 351–359, 2003     

Design and Synthesis of Nitrogen-Rich Azo-Bridged Furoxanylazoles as High-Performance Energetic Materials

A series of novel energetic materials comprising of azo-bridged furoxanylazoles enriched with energetic functionalities was designed and synthesized. These high-energy materials were thoroughly characterized by IR and multinuclear NMR (¹H, ¹³C, ¹⁴N) spectroscopy, high-resolution mass spectrometry, elemental analysis, and differential scanning calorimetry (DSC). The molecular structures of representative amino and azo oxadiazole assemblies were additionally confirmed by single-crystal X-ray diffraction and X-ray powder diffraction. A comparison of contributions of explosophoric moieties into the density of energetic materials revealed that furoxan and 1,2,4-oxadiazole rings are the densest motifs while the substitution of the azide and amino fragments on the nitro and azo ones leads to an increase of the density. Azo bridged energetic materials have high nitrogen-oxygen contents (68.8–76.9 %) and high thermal stability. The synthesized compounds exhibit good experimental densities (1.62–1.88 g cm⁻³), very high enthalpies of formation (846–1720 kJ mol⁻¹), and, as a result, excellent detonation performance (detonation velocities 7.66–9.09 km s⁻¹ and detonation pressures 25.0–37.7 GPa). From the application perspective, the detonation parameters of azo oxadiazole assemblies exceed those of the benchmark explosive RDX, while a combination of high detonation performance and acceptable friction sensitivity of azo(1,2,4-triazolylfuroxan) make it a promising potential alternative to PETN.     

Assembly of Tetrazolylfuroxan Organic Salts: Multipurpose Green Energetic Materials with High Enthalpies of Formation and Excellent Detonation Performance

A series of highly energetic organic salts comprising a tetrazolylfuroxan anion, explosophoric azido or azo functionalities, and nitrogen-rich cations were synthesized by simple, efficient, and scalable chemical routes. These energetic materials were fully characterized by IR and multinuclear NMR (¹H, ¹³C, ¹⁴N, ¹⁵N) spectroscopy, elemental analysis, and differential scanning calorimetry (DSC). Additionally, the structure of an energetic salt consisting of an azidotetrazolylfuroxan anion and a 3,6,7-triamino-7H-[1,2,4]triazolo[4,3-b][1,2,4]triazolium cation was confirmed by single-crystal X-ray diffraction. The synthesized compounds exhibit good experimental densities (1.57–1.71 g cm⁻³), very high enthalpies of formation (818–1363 kJ mol⁻¹), and, as a result, excellent detonation performance (detonation velocities 7.54–8.26 kms⁻¹ and detonation pressures 23.4–29.3 GPa). Most of the synthesized energetic salts have moderate sensitivity toward impact and friction, which makes them promising candidates for a variety of energetic applications. At the same time, three compounds have impact sensitivity on the primary explosives level (1.5–2.7 J). These results along with high detonation parameters and high nitrogen contents (66.0–70.2 %) indicate that these three compounds may serve as potential environmentally friendly alternatives to lead-based primary explosives.     

The uniqueness condition for a weakly periodic Gibbs measure for the hard-core model

We study the hard-core model on the Cayley tree. We show that this model admits only periodic Gibbs measures with the period two. We find sufficient conditions for all weakly periodic Gibbs measures to be translation invariant.     

Structural susceptibility of strength characteristics of polystyrene under uniaxial stretching

The structural susceptibility of the strength characteristics of polystyrene under uniaxial stretching and under test conditions with = const and v_elong = const was studied at 20–100°C. The low structural susceptibility of the durability and durability-equation parameters is due to a change in the elementary fracture volume at different test conditions. It was proposed to characterize the degree of participation of chemical and intermolecular forces by the value U₀/.Moscow Technological Institute of Meat and Milk Industry. Translated from Mekhanika Polimerov, No. 6, pp. 979–984, November–December, 1974.     

Localization of translation-invariant Gibbs measures for the Potts and “solid-on-solid” models on a Cayley tree

We study Potts and “solid-on-solid” models with q ≥ 2 states on the Cayley tree of order k ≥ 1. For any values of the parameter q in the Potts model and q ≤ 6 in the “solid-on-solid” model, we find sets containing all translation-invariant Gibbs measures.