Two Efficient Syntheses of Protected 4‐Deoxy‐D‐lyxo‐hexose (4‐Desoxy‐D‐mannose)

The formation of four differently protected 4‐deoxy‐D‐lyxo‐hexose derivatives 7, 8, 12, and 14 is described. In the first procedure, a nucleophilic displacement of the allylic mesylate 4 by hydride was combined with a highly stereoselective osmylation of olefin 6 to afford diol 7. In the second radical procedure, tributyl tin hydride was substituted by the cheap and environmentally friendly hypophosphorous acid as a hydrogen donor in the reduction of xanthate 13 to 4‐deoxy lyxo‐hexose 14.     

Stamping oriented molecular monolayers using liquid crystal inks

Thermotropic liquid crystal (LC)-based inks are combined with patterned anchoring stamps to deposit organic monolayer films with simultaneous control over positional and molecular orientational order in a single step.     

Drypetdimer A: a new flavone dimer from Drypetes gerrardii

A new flavone dimer, drypetdimer A (1), was isolated from Drypetes gerrardii J.Hutch The structure of the new compound was elucidated by detailed spectroscopic analysis such as 1H, 13C NMR, COSY, HMQC, HMBC and HREIMS.     

Energy level clusters for ν2 + ν3 type combination bands of tetrahedral molecules

Clustering of tetrahedral levels is shown to occur in ν₂ + ν₃ type combination bands of spherical top molecules due to Coriolis and vibrational anharmonic interactions. Cluster correlation diagrams are shown for cases where the vibrational splitting is both large and small compared to the Coriolis splitting, and cluster approximations are given for both cases.     

Acoustic non-linearity for defect selective imaging

Non-linear acoustic effects are of increasing interest in close-to-application research in which mostly ultrasonic frequencies above 1 MHz are used. If the excitation frequency is reduced, one can use high power excitation performed locally by a piezoceramic stack actuator that provides much higher vibration amplitudes. The combination of this excitation with a scanning laser interferometer provides a system for rapidly imaging non-linearities and thereby selectively detecting defects in most kinds of materials. This contribution presents various experimental results showing the potential of this new technique.     

Zirconium-catalyzed amine oxidation: a mechanistic study

The zirconium-catalyzed oxidation of amines in the presence of hydroperoxides gives the corresponding nitro compounds in high yields. In the present paper, we describe mechanistic details of this three-step oxidation, which was investigated by means of DFT calculations. It is shown that N-oxides, hydroxylamines, and nitroso derivatives are formed as intermediates. These compounds had already been postulated on the basis of synthetic experiments. During the oxidation process, the nitrogen atom changes its electronic character from a strong nucleophilic center to a moderate electrophilic center; this is reflected by the geometry of the transition states of the oxygen-transfer process.     

Collective behavior of light-induced droplets in smectic membranes

Collective behavior and organization of droplets in thin smectic membranes were investigated using polarized light microscopy. Droplets were nucleated in membranes by light illumination. We observed the formation of periodic hexagonal and square lattice structures from droplets at large droplet concentration. Nearly linear dependence between period of structure and droplet size was found. We observed that droplets are nucleated on dislocations and periodic chain of droplets may be formed along a dislocation.Received: 29 september 2003, Published online: 5 February 2004PACS: 61.30.Eb Experimental determinations of smectic, nematic, cholesteric, and other structures - 64.70.Md Transitions in liquid crystals - 68.03.Cd Surface tension and related phenomena