Quantum-chemical investigation of some oligomeric heteroaromatic compounds

Those structures of aromatic imidazoles that can be realized in polybenzimidazoles were investigated within the framework of the computational scheme of the Pariser-Parr-Pople method. The features of the electronic structures of the investigated molecules were exposed. A judgment is expressed relative to the strength characteristics of the bonds in the imidazole rings during thermal or thermal oxidative destruction of aromatic polybenzimidazoles. The stereoisomerism of dibenzimidazoles was examined. The UV absorption spectra of the investigated compounds were interpreted.See [1] for communication III.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No, 10, pp. 1396–1402, October, 1973.     

On the characterization of local aromatic properties in benzenoid hydrocarbons

A generalization of the Kekulé index for composite valence structures provides a quantitative value corresponding to Clar's assessment of benzenoid character of aromatic ring systems. The idea involved is further specialized for the individual local rings in the molecules. Comparison with limited experimental data supports the validity of this approach.     

Crystal and molecular structures of the γ-sultones of 1-(3-oxy-4-homoadamantyl)propane-1-sulfonic and 1-(3-oxy-4-homoadamantyl)butane-1-sulfonic acids

A study was carried out on the crystal and molecular structures of the -sultones of 1-(3-oxy-4-homo-adamantyl)propane-1-sulfonicand 1-(3-oxy-4-homoadamantyl)butane-1-sulfonicacids. The configurations of these molecules were established. Contact conformerism of the five-membered rings (C4 and C12 envelopes) is observed at the carbon atom of the sultone ring independently of the length of the alkyl substituent.M. V. Lomonosov Moscow State University. Translated from Zhurnal Strukturnoi Khimii, Vol. 30, No. 6, pp. 85–91, November–December, 1989.     

Crystalline and molecular structures of the alkaloid delcosine

The molecular and crystalline structures of the diterpene alkaloid delcosine (iliensine) have been investigated by x-ray structural analysis. It has been confirmed that the OH group in ring A is located at C(1) and has the orientation. The rings in the molecule have the following conformations: A, B, and D — boat; C and F — envelope; E — chain. The ring linkages are: A/B — trans; A/E — cis; B/C — cis; B/D — cis; B/F — cis. The conformations and linkages of the rings are identical with those observed in lycoctonine.Institute of the Chemistry of Plant Substances, Academy of Sciences of the Uzbek SSR, Tashkent. Translated from Khimiya Prirodnykh Soedinenii, No. 6, pp. 754–758, November–December, 1983.     

Nitration of benzo[g]isoquinoline and its methyl-substituted derivatives

Di- and trinitro derivatives are formed in the nitration under mild conditions (0–5 °C) of benzo[g]isoquinoline and its analogs with a methyl substituent in the pyridine and phenylene rings. The principal reaction products contain a nitro group in the meso position (attached to the C₅ atom) and in the phenylene ring. The structures of the nitro derivatives obtained and the position of the nitro groups in the molecules were proved by means of the PMR, IR, and mass spectra.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 12, pp. 1658–1661, December, 1981.     

Synthetic and modified isoflavonoids. XI. Synthesis of analogues of maxima isoflavone A and xanthocercin

Analogues of maxima isoflavone A and of xanthocercin containing benzodioxolane, benzodioxane, and benzodioxepane fragments in rings A and B of isoflavone have been synthesized. The structures of the compounds obtained have been confirmed by analytical and spectral characteristics.KIEN, Karakalpak Division, Academy of Sciences of the Republic of Uzbekistan, Nukus. Taras Shevchenko Kiev University. Translated from Khimiya Prirodnykh Soedinenii, No. 3, pp. 337–343, May–June, 1994.     

Determination of the bond-angle distribution in vitreous B2O3 by B double rotation (DOR) NMR spectroscopy

The B–O–B bond angle distributions for both ring and non-ring boron sites in vitreous B₂O₃ have been determined by ¹¹B double rotation (DOR) NMR and multiple-quantum (MQ) DOR NMR. The [B₃O₆] boroxol rings are observed to have a mean internal B–O–B angle of 120.0±0.7° with a small standard deviation, σ_R=3.2±0.4°, indicating that the rings are near-perfect planar, hexagonal structures. The rings are linked predominantly by non-ring [BO₃] units, which share oxygens with the boroxol ring, with a mean B_ring–O–B_non-ring angle of 135.1±0.6° and σ_NR=6.7±0.4°. In addition, the fraction of boron atoms, f, which reside in the boroxol rings has been measured for this sample as f=0.73±0.01.     

Visualization of Host–Guest Interactions Between a Modified Nucleoside and Organic Moieties. Crystal Structures of 2'-Deoxy 5'-O-trityluridine and 2'-Deoxy 5'-O-tritylthymidine with Benzene, Toluene, Xylene, Trimethylbenzene, Cyclohexane and Water

This paper describes the crystal structures of 2'-deoxy 5'-O-trityluridine(5'-TU) and 2'-deoxy 5'-O-tritylthymidine (5'-TT) containing different organic moieties. There are two crystallographically independent nucleoside molecules present in the asymmetric units of all the structures. Uracil and thymine bases of the 2'-deoxy 5'-trityl uridine(5'-TU) and all the 2'-deoxy 5'-tritylthymidine structures are in an anti conformation with respect to their furanose rings. Thymine bases of molecules A and B form symmetric self pairs through N(3)-–O(2) hydrogen bonds, whereas uracil bases are not engaged in hydrogen bonding between themselves. Ribose moieties of both molecules of 2'-deoxy 5'-trityithymidine with benzene and toluene are in the C(2')-endo conformations while molecules A and B of 2'-deoxy 5'-tritylthymidine containing xylene, trimethylbenzene, cyclohexane and water are in the C(3')-endo and C(1')-exoconformations, respectively. Both ribose moieties of 5'-TU show C(3')-endo puckering. The conformation about the C(4')-–C(5') bond for all the 2'-deoxy 5'-tritylthymidine structures is g⁺, contrasting with the g^- for the 5'-TU structure. Benzene and toluene molecules stack between TT base pairs, while xylene, trimethylbenzene and cyclohexane are oriented obliquely to the base pairs. 2'-Deoxy 5'-tritylthymidine containing toluene shows a type V C-–H interaction between the methyl group of toluene and the thymine base. Remarkably, the 2'-deoxy 5'-tritylthymidine-containing xylene, trimethylbenzene, cyclohexane and water structures demonstrate a strong type I O-–H interaction between the ribose O(3') and the thymine base seen only in 1.25% of the structures. Molecular packing and hydrogen bonding are discussed.     

Variational method for the calculation of the vibrational structure of the electronic spectra of polyatomic molecules. II

A variational method has been developed to solve the vibrational problem in the excited electronic state and to calculate the vibrational structure of the electronic spectrum of polyatomic molecules. The properties and structural characteristics of the variational matrix have been analyzed and an effective algorithm has been proposed for its approximate diagonalization. The effectiveness of the method and the corresponding suite of programs for the personal computer have been analyzed via the results of model calculations for a number of molecular structures. The method has high precision (errors of about 5% for frequencies and 15% for relative intensities), is an order of magnitude faster than previously used methods, and provides the possibility for the effective solution of the electrono-vibrational problem for polyatomic molecules, including the reverse problem.K. A. Timiryazev Agricultural Academy. Translated from Zhurnal Strukturnoi Khimii, Vol. 34, No. 1, pp. 149–156, January–February, 1993.     

Crystal and molecular structure of salvicin — A diterpenoid acid of the clerodane series

The spatial structure of the diterpenoid salvicin has been determined by x-ray structural analysis. The trans-linkage of rings A/B proposed previously has been confirmed. This indicates that rings A and B in related diterpenoids — salvin and salvinin — also have the trans-linkage.Institute of the Chemistry of Plant Substances, Academy of Sciences of the Uzbek SSR, Tashkent. Translated from Khimiya Prirodnykh Soedinenii, No. 1, pp. 63–68, January–February, 1988.     

13C and1H NMR study of molecular motion in the deoxycholic acid-ferrocene solid inclusion compound

Using solid-state ¹³ C NMR spectroscopy and also measurements of proton spin-lattice relaxation times T ₁ and second moments M ₂ , we have investigated molecular motion in solid inclusion compounds of deoxycholic acid with ferrocene in the interval 100–400 K. We have identified various dynamic processes occurring with participation of molecules of the matrix and the included molecules. We have shown that in addition to rapid reorientations of the cyclopentadienyl rings, the ferrocene molecules undergo 180° jumps about the C ₂ axis. We have determined the parameters for all the molecular motions. We discuss the conformational state of the included molecules.A. N. Nesmeyanov Institute of Heteroorganic Compounds, Russian Academy of Sciences, Moscow 117813. Translated from Izvestiya Akademii Nauk, Seriya Khimicheskaya, No. 3, pp. 586–593, March, 1992.     

Molecular structure of the alkaloid solasodine

An x-ray structural study of the monohydrate of the alkaloid solasodine has been made. Rings A, C, and F have the chair conformation, ring B half-chair, and rings D and E envelope conformations. The linkages of rings B/C and C/D are trans and that of rings D/E cis. It has been shown that solasodine is a diastereomer of the alkaloid tomatidenol.A. N. Nesmeyanov Institute of Heteroorganic Compounds, Moscow. Institute of Organic Synthesis and Coal Chemistry of the Kazakh SSR Academy of Sciences, Karaganda. Translated from Khimiya Prirodnykh Soedinenii, No. 1, pp. 86–88, January–February, 1989.     

Calculations of silicooxygen ring vibration frequencies

In the work model calculations of the vibrations of ideally isolated silicooxygen rings (using PM3 method) have been carried out. three-, four-, and six-membered rings have been considered. It has been found that that the three-membered silicooxygen rings are flat and practically undeformed showing D_3h symmetry. The rings of higher number of ring members (i.e. n>3) are deformed to some extent. The deformation reveals itself most significantly in the Si–O–Si bond angles distribution. In the case of all the rings the bridging Si–O–Si bonds are ca. 0.02–0.04 Å shorter than the non-bridging Si–O⁻ bonds. Hypothetical IR spectra for all the rings considered have been also calculated. Analysis of these hypothetical spectra leads to the conclusion that the whole spectrum can be divided into four wavenumbers regions, 1200–1100 cm⁻¹ stretching Si–O(Si) vibrations; 1000–800 cm⁻¹ stretching Si–O⁻ vibrations; 800–600 cm⁻¹; the region in which a band characteristic of silicooxygen rings appears, and below 600 cm⁻¹ bending ⁻O–Si–O⁻ and (Si)O–Si–O(Si). It has been also found that as the number of ring members increases the ‘ring band’ shifts to lower wavenumbers: 725 cm⁻¹ for three-membered rings, 650 cm⁻¹ for four-membered rings and 610 cm⁻¹ for six-membered rings. Calculated spectra have been compared with the experimental spectra of cyclosilicates. They showed good agreement in the 1200–600 cm⁻¹ region. In the experimental spectra as well as in the calculated ones, with increasing the number of ring members the ‘ring band’ shifts towards lower wavenumbers.     

Structures of three molybdenum(0)–tetracarbonyl–Schiff base compounds

The structures of three molybdenum(0)–tetracarbonyl–Schiff base compounds, determined by X-ray diffraction techniques, are reported. The Schiff bases are those derived from 2-acetylpyridine and 4-methoxyaniline, 4-trifluoromethoxyaniline, or 3-fluoro-4-methylaniline. The structure of the Schiff base ligand has also been determined for the ligand derived from 4-trifluoromethoxyaniline. Comparisons are made between metal–nitrogen bond distances, and carbon–nitrogen and carbon–carbon bond distances in the chelate rings, for these and a number of related molybdenum(0)–tetracarbonyl-diimine compounds. Comparisons are also made between ligand geometry in the free and coordinated states.     

Conformational maps of medium-sized rings

A graphical method of quantitative conformational analysis of medium-sized rings that unites earlier concepts is proposed. This method was used to obtain conformational maps of 6–8-membered rings that make it possible to unequivocally determine the conformations of real rings and to show all possible pathways of conformational transitions without depiction of the individual conformations. This approach made it possible to ascertain previously unknown conformations and pathways of conformational transitions.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 4, pp. 542–559, April, 1988.     

Crystal and molecular structures of cyclohepta(p-phenylene sulfide) and cycloocta(p-phenylene sulfide)

The crystal structures of two cyclic poly(phenylene sulfides) have been determined. The structure of the (p–C₆H₄–S)₁ heptamer contains four crystallographically independent molecules, which are related in pairs by approximate symmetry centers. The molecules in the pairs have similar conformations and form alternating monomolecular layers parallel to the ab plane. The molecule of the (p–C₆H₄–S)₈ octamer has S₄ crystallographic symmetry (a saddle-shaped conformation), and solvent molecules are found in the intramolecular cavities in the crystal.A. N. Nesmeyanov Institute of Organometallic Compounds, Academy of Sciences of the USSR. Translated from Zhurnal Strukturnoi Khimii, Vol. 32, No. 2, pp. 125–132, March–April, 1991.     

Structural features of the copper(II) chloride-triphenylphosphine-N-(2-pyrimidyl)imine complex in crystal and solution

The structure of the copper(II) chloride-triphenylphosphine-N-(2-pyrimidyl)imine complex in crystal and solution was investigated by x-ray analysis and EPR. It was found that despite the difference in the structures of the dissolved and crystalline complexes, the exocyclic nitrogen atom is contained in the coordination sphere of the metal together with the nitrogen atom of the heterocycle in both cases due to the electronic effect of the phosphorus atom. In the crystal, the copper atom is coordinated with two chlorine atoms and two molecules of the ligand, and the distance from the copper cation to the nitrogen atoms of the pyrimidine rings is significantly less than the distance to the nitrogen atoms of the phosphinimine groups (2.0 and 2.8 Å, respectively). The coordination polyhedron formed as a result is a strongly distorted axially asymmetric octahedron. In dissolution, the chlorine anions are substituted by molecules of the solvent, the complex acquires axial symmetry, and four nitrogen atoms from two ligands form a planar square with a copper(II) cation in the center.A. N. Nesmeyanov Institute of Organoelemental Compounds, Russian Academy of Sciences, 117813 Moscow. Translated from Izvestiya Akademii Nauk, Seriya Khimicheskaya, No. 1, pp. 118–125, January, 1992.     

On the molecular structure of the phytochrome chromophore: X-ray analysis of two 2,3-dihydrobilatriene-abc derivatives

The molecular and crystal structures of the two 2,3-dihydrobilatrienes-abc1 and2, representing model compounds for the phytochrome chromophore, were determined by X-ray crystallography at 97 K. Crystals of the racemate1 contain disordered regions. Both molecules are found to be ofall-(Z) configuration, assuming a helical conformation. The acidic hydrogen atoms are localized at the nitrogen atoms of rings A, C and D. A summary of the geometries of unsaturated five-membered rings as observed in four accurate low-temperature crystal structures of bilatrienes-abc is given.Herrn Prof.Josef Schurz zum 60. Geburtstag gewidmet.     

An application of mean-field perturbation theory for the adsorption of polar molecules in nanoslit-pores

In the present research study, we present the development of a model for characterizing and predicting the adsorption of polar molecules between two parallel plates based on mean-field perturbation theory. The electrostatic forces between fluid–fluid molecules in the slit shaped pore are modeled by considering permanent dipole–dipole interactions and permanent dipole-induced dipole moment interactions. The intermolecular potential for the electrostatic interactions was obtained by considering statistical averages over all possible orientations of the molecules. The proposed model is then used to study the sorption of water molecules in the slit shaped pore and an explicit equation for the Helmholtz free energy of the pore phase fluid is derived. Adsorption isotherms for different pore sizes are simulated and the relative contributions of fluid–wall and fluid–fluid interactions to the Helmholtz free energy are calculated as an illustration and compared with the results of existing models in the literature.AMS subject classification: 82B03, 82B05, 82B26, 82B30, 82D15, 31B10, 41A25     

A tandem mass spectrometric study of the N-oxides, quinoline N-oxide, carbadox, and olaquindox, carried out at high mass accuracy using electrospray ionization

A mass spectrometric study of three N-oxides, quinoline N-oxide, and the synthetic antibiotics carbadox and olaquindox, was carried out with a hybrid quadrupole/time-of-flight (TOF) mass spectrometer coupled with electrospray (ES) and atmospheric pressure chemical ionization (APCI) sources. The full scan mass spectra of the N-oxides obtained with ES are similar to those obtained with APCI, and the characteristic fragment ions corresponding to [M+H−O]⁺√ were observed in the full scan mass spectrum of each N-oxide examined. The protonated molecule of each N-oxide was subjected to collision-induced dissociation (CID) and accurate mass measurements were made of each fragment ion so as to determine its elemental composition. Fragment ions generated at enhanced cone voltages upstream of the first mass-resolving element were subjected to CID so as to identify the direct product ion–precursor ion relationship. Plausible structures have been proposed for most of the fragment ions observed. Elimination of OH√ radicals generated from the N→O functional group is a characteristic fragmentation pathway of the N-oxides. The expulsion of radicals and small stable molecules is accompanied by formation and subsequent contraction of heterocyclic rings.