Organofluorosilicates in organic synthesis: XV. Reaction of exo- and endo-5-norbornen-2-ylsilyl derivatives with n-bromosuccinimide. Difference in reactivity between hexacoordinate and tetracoordinate silicon compounds

The reactions of potassium 5-norbornen-2-ylpentafluorosilicate (I) and 5-norbornen-2-yltrimethylsilane (II) with NBS were examined. The former reaction gave 3-nortricyclyl bromide (IV) as the only detectable product, arising from the carbon—silicon bond cleavage. The latter reaction, however, gave 3-bromo-1-nortricyclyltrimethylsilane (V) as the major product, resulting from cleavage of the carbon—hydrogen bond α to silicon, together with IV and an unidentified product. GLC-monitoring of the reactions showed the higher reactivity of the norbornenyl derivative having the leaving group in theendo position irrespective of whether the leaving group is SiF₅ or H. Since no inhibition was observed by the addition of hydroquinone in the dark, the reactions have been regarded as homoallylic electrophilic substitutions. A concerted mechanism seems to be consistent with the experimental data. Cleavage of 1-nortricyclyltrimethylsilane by iodine monochloride to give 1-iodonortricyclene has also been studied.     

483—Monitoring cell potential of Escherichia coli with use of an electrode sensitive to tetraphenyl phosphonium: Change by addition of various sugars

An electrode sensitive to tetraphenyl phosphonium cation (TPP⁺) was applied to the determination of the membrane potential of E. coli (strain B, IAM 1268). This strain did not require EDTA (ethylenediamine tetraacetic acid)-treatment for accumulation of TPP⁺. As reported previously, some part of the TPP⁺-uptake was due to the binding to cell envelopes. The time course of TPP⁺-uptake by cells on addition of sugars was analysed, and the result indicated that the additional binding of TPP⁺ no longer occured. The change in the membrane potential on addition of various sugars was evaluated.     

Thermal conductivity of polytetrafluoroethylene and polytrifluorochloroethylene

Summary Measurements of thermal conductivity were made on polytetrafluoroethylene and polytrifluorochloroethylene which were crystallized by various heat treatments. The variation of thermal conductivity with the degree of crystallinity can be explained qualitatively in terms of the difference of the mean free path. An approximate calculation of the mean free path for the amorphous polytrifluorochloroethylene was made. The calculation gives the value of the mean free path which is very close to the atomic distances in the polymer molecule.

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Zusammenfassung Die thermische Leitf?higkeit von Polytetrafluor?thylen und Polytrifluorchlor?thylen wurde an Proben gemessen, die durch verschiedene W?rmebehandlungen kristallisiert wurden. Die ?nderung der thermischen Leitf?higkeit mit dem Kristallisationsgrad kann qualitativ durch die Unterschiede der mittleren freien Wegl?nge erkl?rt werden. Eine absch?tzende Berechnung der mittleren freien Wegl?nge des Polytrifluorchlor?thylens wurde durchgeführt. Die berechneten Werte liegen nahe an den Atomabst?nden der Polymermoleküle.

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With 4 figures and 1 table

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This article is Part VI of the series “Studies on Thermal Conductivity of High Polymers”. Part I–V of this series were presented in High Polymer Chem., Japan (Kobunshi Kagaku).     

Asymmetric hydrosilylation of olefins catalyzed by a chiral ferrocenylphosphine-palladium complex. Asymmetric synthesis of optically active alcohols and bromides from olefins

Optically active norbornyl and 1-phenylethyl alcohols and bromides were obtained, respectively, from norbornyl- and 1-phenylethylpentafluorosilicates which were prepared by asymmetric hydrosilylation of norbornene and styrene with trichlorosilane catalyzed by a chiral ferrocenylphosphine-palladium complex followed by treatment with potassium fluoride.     

Cyclotron resonance of polarons in AgBr at high microwave fields

A cyclotron resonance experiment on polarons in pure AgBr has been extended to the microwave field of 3 kV cm^?1 by using a pulsed magnetron at 35 GHz at lattice temperatures of 4.2 and 17 K in magnetic fields up to 58 kOe. It was established that the ground state polaron mass is m¹_p(0)=(0.287±0.003)m_e. From microwave field dependences of the peak position and the width of resonance lines, it was established that the electron polaron follows the streaming motion repetitively emitting LO-phonons in the microwave field region above 80 V cm^?1. Further, it was also suggested that, when streaming, the polaron has an enhanced effective mass of (0.353±0.006)m_e rather than the ground state mass m¹_p(0).