Highly Selective Asymmetric Intramolecular Selenocyclisation

Asymmetric intramolecular selenocyclisation of alkenoic acids, alkenols and alkenyl urethanes using chiral ferrocenylselenenyl cations proceeds smoothly to give the corresponding lactones, cyclic ethers and N-heterocyclic compounds, respectively, in moderate yields with very high diastereoselectivities.     

Transient and steady state lateral charge transport in polymeric semiconductors

The Lateral photovoltaic effect (LPE) has been used as an effective tool to probe the dynamics of photogenerated charge carriers in conjugated polymer based optoelectronic devices. In this paper, we analyze the time-dependence of LPE in a position sensing device geometry using a discrete circuit equivalent model coupled with a spreading impedance approach. We elucidate the dependence of the lateral photovoltage (LPV) on the position, intensity and the modulation frequency (ω _c ) of the light beam. Previous experimental results for the position and ω _c dependence of the LPV in the steady state are successfully reproduced within the present approach. We predict a clear knee-like feature in the transient regime of the LPV for high photocurrent values. This feature prompts us to propose that the response time of the organic position sensing device decreases sharply with increasing incident intensity.     

Synthesis and characterization of various phases of cobalt oxide nanoparticles using inorganic precursor

Controllable and uniform doping of nanowires (NWs) is the ultimate challenge prior to their effective application. Si NWs amorphize and bend toward the impinging ions under ion irradiation as a result of viscous flow. We demonstrate that thermal annealing induces a full recovery of the crystalline phase corresponding to the unbending of the NWs. The competition between Solid Phase Epitaxy and Random Nucleation and Growth at the nanoscale is the key parameter controlling the recovery.     

Substituted Diorganotin(IV) O,O’-Alkylene Dithiophosphates: Synthesis and Spectral Aspects

Six new substituted diphenyltin(IV) O,O′-alkylene dithiophosphates, (C₆H₅)₂Sn(X)S(S) POGO [G = —CH₂C(CH₃)₂CH₂—, X = Cl (1), SCN (3), ClO₄ (5); G = —CH₂C (C₄H₉)(C₂H₅)CH₂—, X = Cl (2), SCN (4), ClO₄ (6)], were synthesized by the reaction of the corresponding ammonium salts of the O,O’-alkylene dithiophosphates with an appropriate organotin(IV) chloride. The compounds were characterized on the basis of elemental and spectral analyses (ESI mass spectrometry, IR, ¹H, ¹³C, ³¹P, and ¹¹⁹Sn NMR). The presence of a four-coordinated Sn atom and monodentate O,O’-alkylene dithiophosphate moiety in compounds 1–4 as well as bidentate O,O’-alkylene dithiophosphate unit in compounds 5,6 is established.     

Functionalized Organotellurium Halides: Synthesis,Characterization, and Observation of Intra- and Intermolecular Secondary Bonding

Abstract

Activated tellurium, but not selenium, reacts with para-substituted benzoylmethyl bromides as well as with iodoacetamide at their melting points in absence of a solvent to give bis(p-substituted benzoylmethyl)tellurium dibromides, (p-YC₆H₄COCH₂)₂TeBr₂, (Y = H, Me, and MeO) and bis(acetamido)tellurium diiodide, (H₂NCOCH₂)₂TeI₂, respectively. Quick reduction of (p-YC₆H₄COCH₂)₂TeBr₂, with sodium metabisulphite in a two-phase system yields crystalline (p-YC₆H₄COCH₂)₂Te. These tellurides undergo smooth oxidative addition of halogens, interhalogen ICl or a pseudohalogen (SCN)₂. Intramolecular coordination of the carbonyl group in these functionalized diorganotellurium dihalides is evident from IR spectra and shorter Te···O (carbonyl) distances in comparison to the sum of van der Waals radii and completes six coordination around Te atom. Not unexpectedly, therefore, intermolecular secondary bonding effects of the type Te…O, Te···X and X···X are missing in (PhCOCH₂)₂TeBr₂, (p-MeOC₆H₄COCH₂)TeBr₂ and (PhCOCH₂)₂TeI₂. Instead, these compounds provide rare examples, among organotellurium compounds, of supramolecular architecture, where C–H···Br and C–H···O hydrogen bonds and π-π (phenyl ring) interactions appear to be the noncovalent intermolecular associative forces that dominate the crystal packing.     

On the Reactivity of Metal and Organometallic Halides and Pseudohalides Towards Stannosiloxane (Ph3Sn-O-SiPh3)

Abstract

Interactions of HgX₂ (X = Cl, Br, I, SCN, CN, NCO), SbCl₃, TeCl₄, and PhTeCl₃ with Ph₃Sn-O-SiPh₃ at room temperature have been found to proceed with the simultaneous cleavage of Sn-O and Si-O bonds, invariably yielding Ph₂SnO, Ph₃SiX, and the corresponding organo-mercury, -antimony, and -tellurium derivatives. The course of the reactions suggests the instability of the Sn-O-M (M = Hg, Sb, Te) system.

GRAPHICAL ABSTRACT      

Radical Copolymerization of Acrylonitrile with Methyl Acrylate Complexed by Zinc Chloride

Abstract

The kinetics of the radical copolymerization of acrylonitrile with methyl acrylate complexed by zinc chloride (ZnCl₂) in dimethylformamide (DMF) was investigated at 60, 65, and 70°C. The kinetic data revealed that R_p was an inverse function of ZnCl₂ concentration and directly related to monomers concentration. The increase in the activation energy from 11.85 to 19.25 kJ·mol^?1 and the decrease in the value of the ratio of the propagation to termination rate constants (k_p ²/k_t ) from 0.08 to 0.06 L·mol^?1·s^?1 on the addition of ZnCl₂ indicated its retarding effect. The chain transfer constant of DMF for the system was 16.25 × 10^?4, accordingly the degree of polymerization decreased. The structure and composition of the copolymers determined by ¹H-NMR and elemental analysis was found to be alternating. The nonideal behavior of the glass transition temperatures determined by DSC also favors the alternation of monomer units in the copolymer. The reaction proceeds via a cross-propagation mechanism.     

Crystallizable Polyphenylacetylene-Preparation and Solution Properties

The molecular weight distribution (MWD) of crystallizable polyphenylacetylene prepared near room temperature in the presence of ferric acetylacetonate and triethylaluminum was determined through use of fractions characterized by vapor pressure osmometry and gel permeation chromatography (GPC). The number- and weight-average molecular weights (M _n and M _w) are both less than the molecular weight corresponding to the maximum of the weight distribution function, which lacks a high molecular weight tail. M _wandM _n is less than is consistent with models allowing for chain termination characteristic of vinyl polymers. GPC elution volumes are much less than those characteristic of polystyrene of similar molecular weight, and the Mark-Houwink exponent is high (2.4 for M _v 4800 to 6800). These data indicate more rodlike behavior than for polystyrene of equivalent molecular weight. The MWD and other data suggest intramolecular chain termination, possibly associated with the molecule's tendency to form paramagnetic defect states.     

Barium Manganate Oxidation in Organic Synthesis: Part—IV: Oxidation of Aldehydes to Carboxylic Acids

The oxidation of aldehydes to corresponding carboxylic acids by barium manganate under heterogeneous conditions is described. Aromatic aldehydes were smoothly converted to carboxylic acids while aliphatic aldehydes underwent polymerisation.     

Barium Manganate Oxidation in Organic Synthesis: Part III: Oxidation of Schiff'S Bases to Benzimidazoles Benzoxazoles and Benzthiazoles

The oxidative cyclisation of bsenzylideneamino anilines, phenols and thiophenols to benzimidazoles, benzoxazoles and benzthiazoles respectively using barium manganate is described.