Redox troponization as a novel method for the synthesis of stereoisomeric Eschenmoser's oximes and related non-benzenoid aromatic systems

A novel method for the synthesis of the oxime of 4-methyl-2,4,6-cycloheptatrien-1-one (Eschenmoser's oxime) is proposed. The method involves redox enlargement of the ring of 4-dibromomethyl-4-methyl-2,5-cyclohexadien-1-one oxime through the action of Ni(PPh₃)₄ in DMF (in the presence of Zn). The product is formed as a mixture ofsyn- andanti-forms readily interconverting in solutions. A similar reaction of 4-methyl-4-trichloromethyl-2,5-cyclohexadien-1-one oxime afforded the dimer of agem--centered semiquinoid carbene (1,2-bis-(1-methyl-4-oxyimino-2,5-cyclohexadienyl)-1,2-dichloroethylene), together withsyn- andanti-isomers of 4-chloro-5-methyl-2,4,6-cycloheptatrien-1-one oxime, which are readily separable but also quickly interconverting in solutions. For the latter compounds, the complete¹H NMR assignment of the stereoisomeric structures has been carried out.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 519–523, March, 1995.The authors are grateful to the International Science Foundation (Grant MHW000) as well as the Russian Foundation for Basic Research (Project No. 94-03-08873) for the financial support of the work.     

Determination of total fluoride in HF/HNO3/H2SiF6 etch solutions by new potentiometric titration methods

In the photovoltaic industry the etching of silicon in HF/HNO₃ solutions is a decisive process for cleaning wafer surfaces or to produce certain surface morphologies like polishing or texturization. With regard to cost efficiency, a maximal utilisation of etch baths in combination with highest quality and accuracy is strived. To provide an etch bath control realised by a replenishment with concentrated acids the main constituents of these HF/HNO₃ etch solutions including the reaction product H₂SiF₆ have to be analysed. Two new methods for the determination of the total fluoride content in an acidic etch solution based on the precipitation titration with La(NO₃)₃ are presented within this paper. The first method bases on the proper choice of the reaction conditions, since free fluoride ions have to be liberated from HF and H₂SiF₆ at the same time to be detected by a fluoride ion-selective electrode (F-ISE). Therefore, the sample is adjusted to a pH of 8 for total cleavage of the SiF₆²⁻ anion and titrated in absence of buffers. In a second method, the titration with La(NO₃)₃ is followed by a change of the pH-value using a HF resistant glass-electrode. Both methods provide consistent values, whereas the analysis is fast and accurate, and thus, applicable for industrial process control.     

Selection of terms for a CI wavefunction to preserve potential surface features

A cumulative selection procedure for choosing configuration functions for inclusion in CI calculations is described. The objective of the method is to obtain equal energy loss, relative to unselected calculations, for different states and different regions of the potential surface. Results obtained from calculations on the BH molecule indicate an overall advantage in comparison to the threshold selection procedure, particularly with regard to molecular geometry changes.     

Studies of solvent effects

The effect of water on the conformational preferences of acetylcholine has been studied within the discrete, the continuum and the combined discrete-continuum models described in parts I and II of this series. All the models lead to the conclusion that the trans-gauche form which is, following refined quantum-mechanical computations, the intrinsically preferred one and the one observed in the crystal of acetylcholine and of a number of analogues should remain also the preferred conformation in water. This result agrees with NMR studies. The results of the empirical discrete model used here compare favorably to those obtained by an ab initio super-molecule treatment. The continuum model utilized here represents a net improvement above such models utilized in other works.     

Calculations of the electronic structures of cage molecules using free-electron orbitals as a basis

A non-empirical molecular orbital method, particularly suitable for calculations on cage-like molecules, is described. The method uses as basis functions the set of free-electron functions which are the solutions of Schrödinger's equation for an electron confined between two concentric, spherical potential energy barriers. Application of the theory to the SCF calculation of the energies of the delocalized electrons in benzene and tetrasulphur tetranitride shows that the model is capable of interpreting the properties of such systems. However, it does highlight a difficulty in the calculation of excited state energies with one-centre models which appears to be largely unrecognized.Extension of the method to a consideration of all the valence electrons, using P₄ as an example, reveals problems the origin of which is an inadequate treatment of the core electrons. It is suggested that these problems may best be dealt with by use of a suitable pseudo potential.     

Isocamphananaloge mandelsäure

The synthesis of some new potentially, nitrogenefree spasmolytics is described. Formally the benzene nucleus in some mandelic acid esters, known by their mild spasmolytic activity, is substituted for the isocamphane bicyclus by a) SeO₂ oxidation of 1-(3,3-Dimethyl-2-exo-norbornyl)-ethanone (5) to the corresponding ketoaldehyde6, b) oxidation of6 to the isocamphane analogous mandelic acid4 and c) esterification of derivatives of4 with isoamylalcohol and benzylalcohol. Attemps to dehydrate the methylester7 to camphenylideneacetic acid methylester (12) by various methods failed, probably because of the ring strain.

Teil der Diplomarbeit vonB. Blach, Universität Wien 1981.     

Conductive characteristics of radical‐bearing polythiophenes using a microcomb‐shaped electrode

The electric conductivity of π‐conjugated and radical‐bearing polymers, i.e., polythiophenes bearing pendant galvinoxyl and phenoxyl radical groups, was measured using a microcomb‐shaped electrode. The electric conductivity was found to be enhanced by the radical content in the polymer. The infrared (IR) and Raman spectroscopies suggested a structural change from an aromatic form to a quinoid one in the polythiophene backbone by the phenoxyl radical generation. The effect of the pendant galvinoxyl radical's unpaired electron on the electric conductivity of the polythiophene was discussed by comparing the conductivity of a radical‐bearing polystyrene and a polythiophene mixed with low‐molecular radical molecules. Copyright © 2007 John Wiley & Sons, Ltd.     

A structural analysis of the complexes of (S,S)-dimethylpyridino-18-crown-6 with (R) and (S)-[α-(1-naphthyl)ethyl]ammonium perchlorate by NMR techniques and molecular modeling

Significant - interaction is found in the complexes of (S, S)-dimethylpyridino-18-crown-6 with (R)- and (S)-[-(1-naphthyl)ethyl]ammonium perchlorate. This finding is supported by the¹H NOESY NMR spectral technique, greater chemical shift changes of aromatic protons in both host and guest molecules upon complexation, and by molecular mechanics calculations. Because of the flexibility of the ligand, the tripod hydrogen bonding causes¹³C relaxation times of all periphery carbons to decrease without significant selectivity. Rotational energy barrier calculations of the methyl groups of the complexed ligand also show that the (S, S)-host-(R)-guest is the more stable complex.     

Group 6 tetracarbonyl complexes of N-[(2-pyridyl)methyliden]-α (or β)-aminonaphthalene: Spectral characterization,electrochemistry, solvatochromism and photophysical studies

A new series of group 6 carbonyl complexes of N-[(2-pyridyl)methyliden]-α (or β)-aminonaphthalene (α/β-NaiPy) are described in this work. The complexes are formulated as cis-[M(CO)₄(α/β-NaiPy)] by elemental, mass and other spectroscopic data. The complexes show emission spectra at room temperature and their quantum yield lies between 0.4 and 0.5. All the complexes exhibit negative solvatochromism. Cyclic voltammetry shows metal centred oxidation and ligand reductions.