E/Z Oxime Isomerism in PhC(NOH)CN

The reaction of nitric oxide with benzyl cyanide in the presence of potassium methoxide at low temperature gave the dipotassium salt of a bis‐diazeniumdiolate 2 in excellent yield. Two new stereospecific syntheses of E or Z 2‐(hydroxyimino)‐2‐phenylacetonitrile from 2 have been found. The thermodynamics of the E/Z isomerization has been investigated spectroscopically in solution, in the solid state by differential scanning calorimetry (DSC), and theoretically in the gas phase. Evidence of catalysis by NO of E/Z oxime isomerization has been observed.     

Contact interaction of the borders of edge cracks in a flexible half plane

A singular integral equation method is used to study the closure of edge cracks during bending of an isotropic half space. The cases of a single crack and of a periodic system of cracks perpendicular to the edge of the half space are considered. The effects of the free edge and the spatial period of the cracks on the distribution of the contact reaction and limiting load are investigated. The numerical results are compared with published data obtained without taking crack closure into account, as well as with results on the contact problem for bending of an infinite plate. Ivano-Frankovsk Sector, Institute of Applied Mechanical and Mathematical Problems, National Academy of Sciences of Ukraine. Translated from Teoreticheskaya i Prikladnaya Mekhanika, No. 29, pp. 83–89, 1999.     

Cocrystals of 2-(2,4,5,7-tetranitrofluoren-9-ylidene)propanedinitrile and 2,4,5,7-tetranitrofluoren-9-one with chlorobenzene

Crystallization of 2,4,5,7-tetra­nitro-9-(di­cyano­methyl­ene)­fluor­ene [DTeF; systematic name: 2-(2,4,5,7-tetra­nitro­fluorene-9-yl­idene)­propane­di­nitrile] and 2,4,5,7-tetra­nitrofluoren-9-one (TeNF) from chloro­benzene in the presence of π-donor compounds yielded the chloro­benzene solvate, C₁₆H₄N₆O₈·C₆H₅Cl, and the bis­(chloro­benzene) solvate, C₁₃H₄N₄O₉·2C₆H₅Cl, respectively. Both structures comprise mixed stacks of twisted fluorene moieties interspersed with nearly parallel chloro­benzene mol­ecules. Solvent-free crystals of DTeF and TeNF were obtained from pure chloro­benzene.     

A one-step synthesis of a poly(iptycene) through an unusual Diels-Alder cyclization/dechlorination of tetrachloropentacene

We have discovered the first reaction of a substituted pentacene molecule as a dienophile. A surprisingly clean Diels-Alder self-coupling of Cl4Pn leads to a novel ladder polymer, poly(iptycene), which can be converted to a conducting carbon at relatively low temperature (600-900 degrees C). Theoretical calculations of the former reaction suggest a biradical asymmetric mechanism, despite highly symmetric reactants.     

Kinetic isotope effect and mechanism of catalytic reaction of hydroxybenzenes with epichlorohydrin

Kinetic data are presented for catalytic reactions of 3-nitrophenol and 4,4′-dihydroxydiphenyl sulfone with epichlorohydrin. Magnitudes of the kinetic isotope effects have been determined for these reactions, and a mechanism of catalysis is proposed. Donetsk State University, 24 Universitetskaya ul., Donetsk 340055, Ukraine. Translated from Teoreticheskaya i éksperimental'naya Khimiya, Vol. 34, No. 5, pp. 302–305, September–October, 1998.     

Methylation of sydnone N-oxides: kinetic and thermodynamic control in the alkylation site of an electron-rich heterocycle

Methylation of the anionic 4-methylcarboxy 1,2,3-oxadiazolate 3-oxide occurs at either the disubstituted ring nitrogen or the oxygen of the N-oxide depending upon the conditions and reagents employed. Alkylation with methyl iodide leads to N-alkylation, while dimethyl sulfate gives O-alkylation and trifluoromethanemethylsulfonate gives a mixture of the two products. The regioselectivity of these methylations has been confirmed by X-ray diffraction of the two products, and these are in turn correlated with their theoretically predicted (B3LYP//6-311++G**) relative energies and vibrational spectra. Theoretically, N-alkylation is expected to give an isomer that is over 10 kcal mol-1 more stable than the O-alkylated product. As a neat melt the kinetic O-alkylation product cleanly isomerizes in 2 h when heated to 140 degrees C to give the thermodynamic N-methylated isomer. Taken together the results illustrate the remarkable new sydnone N-oxide derivatives which are readily accessed in this chemistry, with the N-alkylation of the sydnone N-oxide, corresponding to the first case of such an N-alkylation for a diazenium diolate.     

Molecular assembly of rubrene on a metal/metal oxide nanotemplate

We investigated the adsorption properties and self-assembly of rubrene molecules on the copper oxide nanotemplate formed by high-temperature exposure of Cu(110) to molecular oxygen. Using high-resolution scanning tunneling microscopy under ultrahigh-vacuum conditions, we observed a complex variety of self-assembled motifs, driven by competing effects such as the chemical affinity between the organic molecule and the surface, surface coverage, and spatial confinement of the rubrene molecules within the rows of the template.     

Electronic and molecular structures of trigonal truxene-core systems conjugated to peripheral fluorene branches. Spectroscopic and theoretical study

An analysis is performed on the molecular and electronic features in a series of trigonal molecules constituted by a central truxene core which is ramified with three oligofluorene moieties of different lengths. Arms and core are studied independently and upon threefold unification. Special emphasis is paid to the modulation of the conjugational properties in relation to substitution, molecular dimension, ring aromaticity, intermolecular forces, oxidation state, etc. Raman and optical absorption/emission spectroscopies in conjunction with computational theoretical results are combined for this purpose. The evolution of some key intensity ratios in the Raman spectra (i.e., I(1300)/I(1235)) is followed as an indication of electronic interaction between the core and the branches. The changes of the electronic delocalization upon solvation, with varying temperature in the solid state, with the nature of the aromatic unit (bithiophene/fluorene) or after electrochemical oxidation are interpreted. The modulation of the optical properties on the basis of the structure and energetics of the orbital around the gap is also addressed. Density functional theory was used to assign the vibrational and electronic spectra.