Vacancies in the solids of low molecular weight organic compounds observed by positron annihilation

PAL were measured for several low molecular organic compounds, normal and cyclic-hydrocarbons and their perfluorinated ones, from room temperature down to about 40 K, and information about the vacancies in them has been extracted from ₃ andI ₃. Normally the size of vacancies were larger in the solids comprising larger molecules, showing thato-Ps can represent the vacancy size. In a special case of perfluorocyclohexane whose solid had to be prepared by sublimation the vacancy size was larger than expected. In all the solid molecules studied twoo-Ps states could be observed and their relative importance could easily change showing a hysteresis-like behavior. At further lower temperatures of around 40 K theo-Ps state with longer lifetime and larger intensity became overwhelming for all molecules. Also ₃ andI ₃ were not very sensitive to most of the phase transitions, including the melting points.     

Chromium(III) complexes of naturally occurring amino acids

Summary Amino acid complexes of CrCl₃Py₃ have been prepared and studied by elemental analysis, magnetic susceptibility, vibrational (i.r.), electronic and circular dichroism spectroscopy. Two peaks in the visible spectra are assigned to a d-d transition in pseudo octahedral symmetry. The spectrochemical parameters (Dq, B and ₃₅) for the complexes were calculated which confirm that pyridine nitrogen and/or chlorine are not removed. Prolonged heating or bubbling of air through the solution of CrCl₃-Py₃ containing l-(-)-histidine or l-(-)-threonine for several hours enhanced formation of chromium (VI).     

Synthetic strategies and functional reactivity of versatile thiophene synthons

Abstract

Thiophenes are a highly important group of heterocycles and have been of great interest to researchers due to their various reactivities. Many synthetic strategies are used to generate functionalized thiophene derivatives. Several reactions are described, depending on the reactivity of the substituents attached to the thiophene nucleus toward different nucleophiles to yield the versatile thiophene products. Many diverse applications have been utilized for thiophenes from medicinal chemistry to material science.     

Negative ion mass spectra of some unsaturated C-glycosides following keV ion bombardment

A series of anomeric unsaturated C-glycosides were studied by negative ion mass spectrometry following keV ion bombardment The compounds bearing an acidic hydrogen show a prominent [M ? H]^? peak; in the other cases, the [M ? H]^? peak is of very low intensity. A retro-Diels–Alder fragmentation and the abstraction of a hydrogen atom from the aglycon residue are observed in all cases.     

Measurements of Temperatures and Electron Number Density in an Argon–Nitrogen Plasma Jet Generated by a dc Torch-Operation Close to Supersonic Threshold

An investigation of the plasma jet generated by a dc argon–nitrogen plasma torch, operated in association with a controlled-pressure chamber, is presented. The purpose of this article is to describe a study of the properties of a subsonic plasma jet under such operating conditions, when its transition to supersonic flow regime is nearly complete. The goal is that of performing plasma diagnostics not only in the initial region of the jet but also in the downstream region where the plasma emission is weak. For this purpose two different diagnostic methods are used. The first approach is based on non-intrusive optical emission spectroscopy, which yields both excitation and rotational temperatures as well as electron number density fields. The zone investigated by this method extends from the torch exit to about 10 nozzle diameters downstream. The second approach consisted of the use of the intrusive enthalpy probe technique for the measurement of the plasma gas temperature, mainly in the tail region of the plasma jet. In the present work, the effects of axial and radial distances across the jet, on the temperature and electron density profiles are discussed for subsonic flow conditions. Interesting features revealed are the data shown for the various diagnostic methods, which either disagree or overlap with each other. Finally, our results show the need for involving non-equilibrium models for the argon–nitrogen plasma due to the presence of significant differences between the temperatures of light and heavy particles.     

Polarographic behaviour and determination of paracetamol and salicylamide after treatment with nitrous acid

A polarographic procedure is described for the determination of paracetamol (acetaminophen) and salicylamide after treatment with nitrous acid. The different experimental parameters affecting the derivatization process and the polarographic analysis were studied. The derivatization products were found to be reduced at the dropping mercury electrode over the whole pH range in Britton-Robinson buffers. At pH 7.0, well defined diffusion-controlled cathodic waves were produced for both compounds. Plots of limiting current vs. concentration were linear over the ranges 0.05–0.75 and 0.25–1.5mM for paracetamol and salicylamide, respectively, in the d.c. mode, with minimum detectability of 2.5 × 10^–6 and 1.25 × 10^–5 M, respectively. The procedure was applied to the analysis of some pharmaceutical dosage forms and the results were in good agreement with those obtained by official and compendial methods.     

Kinetics of Oxidation of 4-Oxoacids by <Emphasis Type="Italic">N</Emphasis>-Chlorosaccharin in Aqueous Acetic Acid Medium

The oxidation kinetics of substituted and unsubstituted 4-oxoacids (S) by N-chlorosaccharin (NCSA) have been studied in aqueous acetic acid media. The reaction follows first-order kinetics in each of the 4-oxoacids, NCSA and H⁺. The effect of changes in the electronic nature of the substrate reveals that positive charge develops in the transition state. Based on the kinetic results and product analysis, a suitable mechanism has been proposed for the reaction of NCSA with 4-oxoacids.     

Synthesis of thienothiazocinoisoindolediones and thienothiazinoisoindolones from mercaptothiophenes and chloromethylphthalimide

2-Thienylthiomethylphthalimides 3a,b were synthesized by action of Chloromethylphthalimide on 2-or 3-mercaptothiophene. Reduction of 3a,b and Wittig reaction using carbethoxycarbonyltriphenyl-phosphorane gave the corresponding acetic acids 5a,b which cyclized under Friedel and Crafts conditions to lead the thienothiazocinoisoindolediones 6a,b. Thienothiazinoisoindolones 7a,b were obtained from hydroxyisoindolones derivatives 4a,b in acid conditions via an acyliminium ion.