Around a theorem of F. Dyson and A. Lenard: Energy equilibria for point charge distributions in classical electrostatics

We discuss several results in electrostatics: Onsager’s inequality, an extension of Earnshaw’s theorem, and a result stemming from the celebrated conjecture of Maxwell on the number of points of electrostatic equilibrium. Whenever possible, we try to provide a brief historical context and references.     

Practical synthesis of (Z)-polyaromatic and heteroaromatic vinylacetylenes

[reaction: seet text] Two synthetic routes to several (Z)-polyaromatic and heteroaromatic substituted vinylacetylenes are described. The nature of aryl- or heteroaryl-substituted carboxaldehyde used as starting material dictated the choice of Wittig salt employed. A very attractive way to construct polyaromatic and pyridine-containing enynes is the reaction of polyaromatic and pyridine-containing aldehydes with bromomethyltriphenylphosphonium bromide in the presence of potassium tert-butoxide followed by a Sonogashira desilylation procedure (method B).     

Development of a HPTLC method to profile the phytochemicals in Allanblackia parviflora (tallow tree) kernel and seed cakes

HPTLC is a useful and practical analytical tool to characterize plant compositions. This study was focused on exploring the results of high-performance thin-layer chromatography (HPTLC) analysis, particularly as a useful tool for the authentication of Allanblackia parviflora seed and kernel cakes. Bulked samples from sixteen different Ghanaian communities were analysed by HPTLC and their fingerprints were compared. The optimum experimental conditions were established: sample weight of 2.0 g, methanol:water (80:20 v/v) as extraction solvent, 30 min extraction time and twice extraction, ethyl acetate:methanol:water (100:16.5:13.5 v/v) as mobile phase, vanillic acid as derivatisation agent and 7 min of plate heating time after derivatisation. The HPTLC profile generated from extracts across 16 communities and 157 trees was very reproducible and demonstrates the robustness of the technique in characterising the profile.

     

Four-component couplingvia a sequence of threeAd E reactions involving arenesulfenyl chloride, two alkyl vinyl ether units, and silicon-containing π-donors as a method for the synthesis of polyfunctional compounds

A protocol for the synthesis of polyfunctional compounds by a Lewis acid initiated tandem sequence of threeAd _E reactions of sulfur-containing electrophiles with two alkyl vinyl ether units and silicon containing π-donors is proposed. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya No. 5, pp. 924–932, May, 1998.     

Direct synthesis of monofunctionalized indolizine derivatives bearing alkoxymethyl substituents at C-3 and their benzofused analogues

[reaction: see text] Treatment of (Z)-2-pyridine and quinoline silylated vinylacetylenes at reflux with several alcohols in the presence of a suitable inorganic base (KOH, K2CO3, CsF, or KF) serendipitously gave 3-alkoxylmethylindolizines and the corresponding 1-alkoxymethylpyrrolo [1,2-a]quinolines and not the anticipated desilylated vinylacetylene derivatives. A mechanistic possibility for this unexpected chemical transformation is suggested.     

Multi-element analysis of Ghanaian crude oils by instrumental neutron activation analysis

Instrumental neutron activation analysis based on thermal neutrons from the Ghana Research Reactor-1 facility was utilized to analyze 18 trace elements namely Al, As, Br, Ca, Cd, Cl, Co, Cu, Fe, K, Mg, Mn, Na, Ni, S, Si, V, and Zn in two different crude oil samples from the Saltpond and Jubilee field in the Saltpond, Central region and Cape Three Points, Western region of Ghana, respectively. The sulfur concentration for both samples were low and within globally accepted range of 0.1–0.5%wt for sweet crude oil. The results of the elemental analysis showed that the two samples are relatively low in trace element concentrations compared to crude oils of other countries. Higher Fe concentration in the Jubilee crude oil indicates younger oil. The V/Ni ratios obtained for crude oils from both locations imply a possible marine organic origin and also suggest the Saltpond crude oil is more matured than the Jubilee crude oil.