Bile-Acids in Asymmetric-Synthesis.2. Cholic-Acid Derived Novel Chiral Auxiliaries For Asymmetric Diels-Alder Reactions

Cholic acid-based chiral acrylate 5 yields a Diels-Alder adduct with cyclopent

Chiral polyhydroxylated tetrahydrothiophene derivatives: novel synthesis and structural elucidation by X-ray crystallography, NMR spectroscopy and molecular mechanics calculations

The dideoxygenation reaction of 1,3;4,6-di-O-alkylidene-2,5-di-S-methylthiocarbonyl-D-mannitol derivatives under Barton-McCombie reaction conditions gave the hexahydrodipyranothiophenes 4 and 7 instead of the expected 2,5-dideoxy products. Structural and conformational information on these novel derivatives has been obtained by NMR spectroscopy, single-crystal X-ray crystallography and molecular mechanics calculations.

Dielectric friction and solvation dynamics: Novel results on relaxation in dipolar liquids

In this article we present a new, general but simple, microscopic expression for time-dependent solvation energy of an ion. This expression is surprisingly similar to the expression for the time-dependent dielectric friction on a moving ion. We show that both the Chandra-Bagchi and the Fried-Mukamel formulations of solvation dynamics can be easily derived from this expression. This expression leads to an almost perfect agreement of the theory with all the available computer simulation results. Second, we show here for the first time that the mobility of a light solute ion can significantly accelerate its own solvation, specially in the underdamped limit. The latter result is also in excellent agreement with the computer simulations.

Interferometry with a novel composite material

An interesting application of optical phase conjugation is phase conjugate interferometry. We report here a new approach to real-time interferometry which combines the high phase conjugate efficiency of photorefractive crystals and the fast response times offered by dye-doped polymer films by using a composite structure. The ability of this material to generate two independent but overlapping phase conjugate waves. which can interfere to reveal the phase changes in a test object, is discussed and demonstrated with a specific example.

K1-xLaxCa2-xNb3O10, a Layered Perovskite Series with Variable Interlayer Cation Density, and LaCaNb3O10, a Novel Layered Perovskite Oxide with No Interlayer Cations

A series of layered perovskite oxides of the formula K1-xLaxCa2-xNb3O10 for 0 < x ≤ 1.0 have been prepared. All the members are isostructural, possessing the structure of KCa2Nb3O10. The interlayer potassium ions in the new series can be ion-exchanged with protons to give H1-xLaxCa2-xNb3O10. The latter readily forms intercalation compounds of the formula (CnH2n+1NH3)1-x LaxCa2-xNb3O10, just as the parent solid acid HCa2Nb3O10. The end member LaCaNb3O10 containing no interlayer cations is a novel layered perovskite oxide, being a n = 3 member of the series An-1BnX3n+1.

Mechanical alloying—a novel synthesis route for amorphous phases

Mechanical alloying (MA) pioneered by Benjamin is a technique for the extension of solid solubility in systems where the equilibrium solid solubility is limited. This technique has, in recent years, emerged as a novel alternate route for rapid solidification processing (RSP) for the production of metastable crystalline, quasicrystalline, amorphous phases and nanocrystalline materials. The glass-forming composition range (GFR), in general, is found to be much wider in case of MA in comparison with RSP. The amorphous powders produced by MA can be compacted to bulk shapes and sizes and can be used as precursors to obtain high strength materials. This paper reports the work done on solid state amorphization by MA in Ti-Ni-Cu and Al-Ti systems where a wide GFR has been obtained. Al-Ti is a classic case where no glass formation has been observed by RSP, while a GFR of 25–90 at.% Ti has been obtained in this system, thus demonstrating the superiority of MA over RSP. The free energy calculations made to explain GFR are also presented.

Novel mechanism for high speed growth of transparent and conducting tin oxide thin films by spray pyrolysis

A novel mechanism is proposed for efficient manipulation of transport forces acting on the droplets during spray pyrolytic deposition of thin films. A ‘‘burst mode’’ technique of spraying is used to adjust the deposition conditions so as to transport the droplets under the new mechanism. Transparent, conducting thin films of undoped tin oxide prepared by this method showed significant improvement in growth rate. The films are found to be of fairly good quality with optical transmission of 82% and sheet resistance of 35 Ω/☒. The films are chemically homogeneous and grow preferentially along 〈200〉 direction.

Novel photocrosslinkable liquid-crystalline polymers: poly[bis(benzylidene)] esters

A new class of photo-cross-linkable main-chain liquid crystalline polymers (PMCLCPs) containing bis(benzylidene)cycloallranone groups have been synthesized and studied for their liquid crystalline and photochemical properties. The bis(benzylidene)cycloalkanone group in the chain functions both as a mesogen and as a photoreactive center. All of the polymers exhibit a nematic mesophase. Two kinds of photoreactions, namely, photoisomerization and photo-cross-linking, operate in these polymers. Above Tu at the initial stages of irradiation, photoisomerization predominates the cross-linking, which resulta in the disruption of the chromophore aggregates. Below T8, because of the restricted mobility of the chains, only cross-linking takes place. Studies on the model compound, bis(benzylidene)cyclopentanone, confii the above observations and demonstrate further that the cross-linking proceeds by the 2r + 2r cycloaddition reaction of the bis(benzylidene)cycloallranone moieties. The cross-linking rate decreases with increase in the size of the cycloalkanone ring. Heating the solution cast polymer fii results in the ordered aggregation of the chromophores just above TI and also at the crystal to crystal transition temperature, which facilitates the phobcross-linking reactions. In the isotropic phase, the random orientation of the chromophores drastically curtails the cross-linking rata

Novel polymeric flame retardant plasticizers for poly(vinyl chloride)

Polyphosphate esters have been used as polymeric flame retardant plasticizers in poly(vinyl chloride); thermal and flammability studies were carried out to evaluate their efficiencies as fire retardants. A comparison is also made on the fire retardancy of the conventional simple phosphates with that of the polyphosphates as novel fire retardant plasticizers for PVC.

Reaction of spironaphthalenones with hydroxylamine: Part III. A novel mechanism for the formation of products and trapping of an intermediate.

A mechanism involving the intermediacy of nitrene 5, formed from the oxime of spironaphthalenone 1 by acid catalysed dehydration, has been proposed to explain the formation of pyrrolotropones/pyrrolo esters from spironaphthalenones. The initially formed nitrene rearranges to the isopyrrole 6, which either undergoes sigmatropic migration to the pyrrolotropone 2 or adds alcohol to form the pyrrolo ester depending on substitution at 1′ position. The isopyrrole intermediate 6 has been trapped as a Diels-Alder adduct 8.

Solvation dynamics in liquid water. A novel interplay between librational and diffusive modes

A microscopic calculation of the solvation dynamics of an ion in liquid water is presented. The calculated solvation time correlation function shows an ultrafast Gaussian decay which carries about 70%–90% of the strength followed by a biexponential decay with time constants equal to 250 fs and 1 ps. These results are in excellent agreement with the computer simulations of Maroncelli and Fleming and also with the experimental findings of Barbara and Jarzeba. In addition, we find that both the rotational librations and the intermolecular translational vibrational modes of water contribute significantly to the initial Gaussian decay.

Stereoelectronic control of Cope rearrangement energetics through remote double bonds in novel, rigid polycyclic frames

The presence and orientation of remote double bonds are shown to completely alter the shapes of Cope rearrangement energy profiles in a heptacyclic system.