New methodology for the deoxygenative difluoromethylenation of aldehydes and ketones; unexpected formation of tetrafluorocyclopropanes

Generation of difluoromethylene phosphorus ylides in the presence of aldehydes and ketones results in Wittig-type reactions to give gem-difluoroalkenes. Subsequent in situ addition of difluorocarbene (carbenoid) can occur (increased with triphenylphosphine and decreased with tributylphosphine) to give tetrafluorocyclopropanes. [Reaction: see text]     

Synthesis and properties of gem-(difluorocyclopropyl)amine derivatives of bicyclo[n.1.0]alkanes

[reaction: see text] Generation of difluorocarbene(carbenoid) in the presence of enamines derived from cyclic ketones results in overall insertion of CF2 to produce bicyclic difluorocyclopropylamines. These adducts are very weakly basic, and their thermal stabilities vary markedly with their structures.     

Cubane-like structure of a silanethiol--primary amine assembly--a novel, unusual hydrogen bond pattern

A reaction of silanethiol and primary amine leads to a product whose crystals are built of well-defined supermolecules--assemblies of four ammonium silanethiolate units (RS(-)H(3)N(+)R')(4) with a novel, unusual 3D hydrogen bond pattern.     

High-resolution solid-state 119Sn and 195Pt NMR studies of MPtSn semiconductors (M = Ti, Zr, Hf, Th)

Solid-state 119Sn and 195Pt magic-angle spinning (MAS) NMR spectra are reported on a series of MPtSn compounds (M = Ti, Zr, Hf, Th). In favorable cases (TiPtSn and ZrPtSn) the spectra reveal expected J-coupling patterns originating from indirect spin coupling between Pt and Sn nuclei. MAS has no effect on the broad and asymmetric spectra of either 119Sn and 195Pt nuclei in HfPtSn.     

Results for neutral to charged current cross section ratios from ν and\bar v nucleus interactions below 30 GeV

Using the freon filled bubble chamber SKAT in the (anti)neutrino wide band beam of the Serpukhov accelerator we determine the neutral to charged current cross section ratios for neutrinos and antineutrinos below 30GeV. From these ratios we calculate in leading order a mixing parameter of the standard model of Θ _w =0.215±0.029.     

Nanoscale atomic lithography with a cesium atomic beam

2 line (852 nm) and a width of about 120 nm and covering a large area of approximately 1 mm². Received: 3 July 1997/Accepted: 7 July 1997     

Ein dreidimensionales Gitterpunktproblem

As a generalization of the sphere problem (cf. VINOGRADOV [7]) the present paper deals with estimates for the number of lattice points (points of the space with integral coordinates) in regions defined by x^a+y^a+z^a≦R^a, x≧0, y≧0, z≧0. In particuliar, the case 02 has been treated by KRÄTZEL [2]), and it appears that the exact asymptotic behaviour of the remainder term can be determined. Furthermore an asymptotic expansion of the remainder term is established containing the more valid terms the smaller the exponent a is.     

Gitterpunkte in Bereichenx n +y m ≤R,x≥0,y≥0

This paper deals with estimates for the number of lattice points (i. e. points of the plane with integer coordinates) in the domains indicated above. For a wide class of real exponentsn andm the exact order of magnitude of the error term is determined and its behaviour for growingR is discussed.