Molecular structures of some hydroxyazo compounds and their derivatives

The i.r. absorption spectra of 14 o-hydroxyazophenyl derivatives with increasing number of fused benzene rings of the aryl moiety are studied in solid state, in CCl₄ solution and in nujol mull. The i.r. spectral bands are assigned and indicate that these compounds exist in two tautomer forms. The OH group of the aryl moiety ortho to the azo group is responsible for the hydrazone structure. If solutions in CCl₄ are exposed to sunlight the strongly coloured compounds undergo a rapid bleaching, leading to a destruction of the azo group accompanied by an increase of hydrazone structures.     

Pulse mechanochemistry of organoelement compounds

The results of studies of fast mechanochemical reactions initiated by elastic wave pulses (EWP) of 100 μs duration on polycrystalline mixtures under high pressures (4–25 kbar) are summarized. A possible mechanism of the EWP-initiated processes was proposed. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya. No. 9, pp. 1621–1635, September, 1999.     

Prediction of toxicity of nitroaromatic compounds through their molecular structures

In this paper, a new simple method is presented for the estimation of the toxicity of nitroaromatic compounds including some well-known explosives. This method can predict the 50% lethal dose concentration for rats (LD ₅₀) as the estimation of toxicity in vivo. The prediction of LD ₅₀ of nitroaromatics through a new general correlation is based on the number of alkyl and nitro groups per molecular weight of the nitroaromatic compound as a core function. The existence of some specific structural parameters can decrease or increase the predicted results on the basis of the core function. The predicted results of various nitroaromatic compounds afford reliable prediction of LD ₅₀ with respect to experimental data. Prediction of toxicity for 28 nitroaromatic compounds, where the experimental data were available, and new nitroaromatic derivatives produce comparable results to those of several models of Quantitative Structure Activity Relation (QSAR).     

The localized electrons detector as an ab initio representation of molecular structures

The local single particle momentum is proposed as a localized‐electrons detector (LED) that provides a direct three‐dimensional representation of bonding interactions in molecules. It is given exclusively in terms of the electron density and its gradient. We show that the graphical representation of bonding interactions given by LED is consistent with the local curvatures of the electron density as given by the eigenvalues of the Hessian matrix, according to a local symmetry classification of the critical points here introduced. LED consistently complements the topological analysis of the electron density given by the quantum theory of atoms in molecules, by providing a graphical representation of the symmetry of the bonding interactions in molecular systems. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem 110:2418–2425, 2010     

Molecular shapes and molecular structures

The first part is a response to E.B. Wilson's remarks about molecular structure at the 1979 Sanibel Symposium; his proposed extension of the notion of “potential energy surface” is a convention, not a part of fundamental molecular quantum theory. An energy surface has no essential role in a non-adiabatic theory which, both in principle and practice, can account for the spectroscopic term formulae with greater accuracy than models based on PE surfaces. Results obtained from the generator coordinate method are cited as confirmation of this conclusion. Claverie and Diner's distinction between “quantum structure” and “classical molecular structure” is discussed; it is the latter that is problematic in molecular quantum theory. The use of molecular structure is optional, and determined by utility, rather than essential in chemical physics; photoelectron spectroscopy is an example where this appreciation has proved fruitful.     

A unique computer representation for molecular structures

Converting a non-unique connection table to a unique (canonical) name can be accomplished by assigning unique sequence numbers on the basis of topological (constitutional) properties. An algorithm is reported which performs this task by perceiving the topological symmetry of the molecule. A convention for assigning a single name to topologically unique structures which vary only in the position of π-electrons (resonance forms) is also presented.     

Electrochemical activation of inorganic and simplest organoelement compounds in organic syntheses

Data are presented on the reactivity of silicon and tin hydrides, phosphorus trichloride, and hydrogen sulfide in the anodic single-electron reduction of these reagents to corresponding radical cations. Organic reactions involving them are considered.     

Synthesis by Si-H bond lithiation of novel half-pincer and pincer silyllithium compounds and their molecular structures

Structural Chemistry - The synthesis and the X-ray structural analysis of novel pincer and half-pincer silyllithiums: Ar2 (N)(tBu2MeSi)SiLi (Ar(N) = o-dimethylbenzylamine) (2a),...     

Hydrogallation of alkynes with H-GaCl2: formation of organoelement dichlorogallium compounds potentially applicable as chelating Lewis acids

Treatment of trimethylsilylethynylbenzenes C6H6-x(C[TRIPLE BOND]C-SiMe3)x(x=1-3) with the hydridodichlorogallium compound H-GaCl2 afforded, almost quantitatively, the alkenylphenyl compounds C6H6-x[C(H)C(SiMe3)-GaCl2]x[x=1 (6), 2 (7), and 3 (8)] by hydrogallation. Only compound 6 was readily soluble in n-hexane; it formed dimers via Ga-Cl bridges. The bisalkenyl compound 7 was only sparingly soluble; its molecular structure consisted of a singular dimeric formula unit with a cyclophane-type constitution and two bridging Ga 2Cl 2 heterocycles. The overall structure may be described by a molecular box formed by a large macrocycle comprising 22 Ga, C, and Cl atoms. Compound 8 proved to be insoluble in hydrocarbon solvents. Its molecular structure could not be detected. Extraction of the solid raw products of 7 and 8 with diethyl ether yielded small quantities of the ether adducts C6H6-x[C(H)C(SiMe3)-GaCl2(OEt2)]x(x=2, 3) [7(OEt2)2 and 8(OEt2)3], both of which are monomeric because of the coordinative saturation of their gallium atoms. The tetraalkyne 1,2,4,5-tetrakis(trimethylsilylethynyl)benzene gave a different reaction course. Complete hydrogallation resulted in the release of 2 equiv of GaCl3, and neighboring alkenyl groups of the product 9 were connected by GaCl bridges to form seven-membered heterocycles and an overall tricyclic compound. Compound 9 was characterized as a diethyl ether adduct.     

Production of positron emitters and application of their labeled compounds to plant studies

The positron emitters¹¹C,¹³N and¹⁸F and their labeled compounds have been produced for studies on plants using a newly developed positron emitting tracer imaging system. Although this system covers, at present, a limited area in a plant, the distribution of the positron emitter fed into the plant can be visualized dynamically. Further development of positron-emitter-labeled compounds is expected to elucidate the physiological function of plants in vivo.     

On 3D graphical representation of RNA secondary structures and their applications

In this article, we proposed a 3D representation of RNA secondary structures. Based on this representation, we outline an approach by constructing a 3-component vector whose components are the normalized leading eigenvalues of the L/L matrices associated with RNA secondary structure. The examination of similarities/dissimilarities among the secondary structure at the 3’-terminus of different viruses illustrates the utility of the approach.     

IR-photodissociation of size selected molecular clusters and their structures

Infrared photodissociation spectra of (CH₃NH₂) _n clusters were measured fromn=2 ton=6 near the monomer absorption of the C-N stretching mode at 1044 cm^?1 using a cw-CO₂ laser. The clusters were size-selected by scattering from a helium beam. The spectrum of cold dimers shows a red (1038 cm^?1) and a blue (1048 cm^?1) shifted peak which is attributed to the non-equivalent position of the C-N in the open dimer structure. The larger clusters exhibit only one peak between 1045.4 cm^?1 and 1046.0 cm^?1 caused by the equivalent position of the C-N in the cyclic structures of the larger clusters. Structure calculations confirm these results. Secondly, the mixed complexes C₂H₄-CH₃COCH₃ and C₂H₄-(CH₃COCH₃)₂ were investigated. The dimer spectrum, measured around the monomer frequency of the out-of-plane bending mode of C₂H₄ at 949 cm^?1, shows two peaks at 946.2 cm^?1 and 961.3 cm^?1. This splitting is attributed to two different isomers that are found in configuration calculations. A similar behaviour is found for the trimer.     

Molecular structures of mononitroanilines and their thermal decomposition products

The molecular structures of 2-nitro, 3-nitro, and 4-nitroaniline and their internal rotational isomers were calculated by anab-initio method using HF/6-31G* basis set. The geometries were influenced by the nitro group's position. The perturbation of the amino group on the nitro group was observed in a 2-nitroaniline isomer having a molecular structure distinct from that of the other two isomers. Among them, 4-nitroaniline is the most stable one. Internal rotation tests of either the nitro or amino group of 3-nitro and 4-nitroaniline indicate that no significant deformations of the phenyl ring occurred after internal rotation; however, the internal rotational isomers of 2-nitroaniline differed from its original structure. Relatively easier internal rotation of the nitro group than the amino group and different C-NO₂ and C-NH₂ bonds indicate the bond-breaking message of nitroanilines. As products of explosives induced by thermal or shock are of interest, five products of 2-nitroaniline were selected to assess their geometries and energies. The above calculations revealed that these products are thermodynamically unfavorable.     

Molecular polarizability of organic molecules and their complexes: LIV. Molar volumes of polyaryl organoelement compounds in solutions,extrapolated to infinite dilution,and steric structure of the molecules

Molar volumes in various solvents were determined for organic derivatives of silicon, phosphorus, arsenic, sulfur, and tellurium, containing aryl nuclei capable to internal rotation about single bonds between them and bridging groups. Additive analysis of the molar volumes of these compounds showed that the aryl nuclei are acoplanar with respect to the bridging groups. Most probable is a conrotatory mutual orientation of the aromatic rings. Molar volumes were also determined for a series of compounds with two bridging groups, which can serve as models of an extreme case of mutual proximity of aryl ring planes in diaryl systems with one bridging group. A possibility for considerably simplifying the methods for determination of dipole moments and Kerr constants for compounds whose molar volumes can be calculated by our developed additive scheme is demonstrated.     

Liquid crystalline compounds with V-shaped molecular structures: synthesis and characterization of new azo compounds

The synthesis and mesomorphic properties of a series of 1,2-phenylene bis[4-(4-alkyloxyphenylazo)benzoates] are reported. The mesophases exhibited by these bent-shaped azo compounds are identified as nematic, smectic A and crystal E phases. All these compounds have fairly low transition temperatures, and so are suitable for physical studies. It has been concluded that the -CH N- linkage can be more conducive to mesomorphism compared with the -N N- linkage.     

环孢霉素A与小分子化合物的超分子识别作用

环孢霉素A(Cyclosporin A)是一种20世纪80年代引入临床的新的十一环多肽抗生素.因其毒性小,有较高的选择性,在临床上将其用于脏器移植中抗排异反应的首选免疫抑制剂.     

Mannich bases as model compounds for intramolecular hydrogen bonding I. Solid state structures and molecular calculations

Summary A survey of the structures and the properties of the hydrogen bonds inortho-aminomethylphenols and -naphthols in the solid state is presented. The results are compared with molecular structure calculations. The solid state complexes can exist in the molecular or in zwitterionic form. In the last case, only intermolecular hydrogen bonds forming cyclic dimers or linear chains were detected.

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Mannich-Basen als Modelle für Intramolekulare Wasserstoffbrücken, 1. Mitt. Festkörperstrukturen und Molekülrechnungen

Zusammenfassung Eine Übersicht über Strukturen und Eigenschaften von Wasserstoffbrücken inortho-Aminomethylphenolen und -naphtholen wird präsentiert. Die Ergebnisse werden mit Molekülrechnungen verglichen. Im Festkörper existieren diese Verbindungen in neutraler oder in zwitterionischer Form. Für den zweiten Fall können nur intermolekulare Wasserstoffbrücken nachgewiesen werden, und zwar in Dimeren oder in linearen Ketten.

     

Chemistry of organosilicon compounds: CIV. Syntheses of novel organoelement heterocycles containing titanium and silicon

Four new dicyclopentadienyltitanium(IV) metallocycles, Cp₂TiCH₂XCH₂ (X = SiMe₂OSiMe₂, SiMe₂CH₂SiMe₂, SiMe₂SiMe₂, and SiMe₂SiMe₂SiMe₂) are prepared and characterized.