Asymmetrische diorganoalkoxyzinnhydride und ihre anwendung als stereoselektive reduktionsmittel

The asymmetric diorgano(alkoxy)tin halides RR′Sn(OC₁₀H₁₉)X and RR′Sn-(OC₁₀H₁₇)X were synthesized by the reaction of diorganotin halides with sodium l(?)mentholate and sodium l(?)borneolate. Reduction of these asymmetric diorgano(alkoxy)tin halides yields the optically active diorgano(alkoxy)tin hydrides RR′Sn(OC₁₀H₁₉)H and RR′Sn(OC₁₀H₁₇)H, which are used for the asymmetric reduction of racemic haloalkanes.     

Branching random walks I

A general method is developed with which various theorems on the mean square convergence of functionals of branching random walks are proven. The results cover extensions and generalizations of classical central limit analogues as well as a result of a different type.     

Nuclear spin conversion of methane in pure and rare-gas mixed crystals

Spin species conversion has been observed by means of neutron scattering. Methane, matrixisolated in rare-gas crystals has been investigated by measuring the time dependence of the detailed balance factor of inelastic neutron spectra. The temperature dependence of conversion rates in the interval between 2 and 5 K turns out to be stronger than predicted by a single phonon process. In general, conversion times are of the order of hours in this temperature region. The influence of the matrix is well described by a coupled phonon density of states. Crystals of pure and krypton doped methane have been examined by measuring the time dependence of the total neutron scattering cross section. For pure methane, the temperature dependence of the conversion rates shows two regimes for both free rotator and ordered molecules. Below 5 K, the behavior is described by a single phonon process and above by an Arrhenius law. Rates are enhanced by krypton dotation, which is explained by changed level spacings due to orientational disorder.