Barriers to rotation in methyl formate by dynamic NMR spectroscopy and barriers to 1,3 oxygen-to-oxygen migration in methyl formate and trifluoromethyl formate by ab initio calculations

Free-energy barriers of 9.85 and 11.91 +/- 0.15 kcal/mol at -70.8 degrees C were found by dynamic NMR spectroscopy for the E-to-Z and Z-to-E conversions, respectively, of methyl formate (1) enriched in 13C to 99% for the carbonyl carbon [methyl formate 13C (2)]. These barriers are higher than the literature values reported for -53 degrees C. The free-energy barrier to 1,3 oxygen-to-oxygen migration of the methyl group in methyl formate was determined by ab initio calculations at several levels. The value of 58.7 kcal/mol obtained at the MP2/6-311+G (df,pd) level was compared to a literature barrier for this process (MINDO/3) and to barriers for related compounds. A free-energy barrier of 63.0 kcal/mol for the oxygen - to - oxygen migration of the CF3 group in trifluoromethyl formate (3) was calculated at the MP2/6-31+G level.     

New Synthesis of 1-Aryl-4-(4-hydroxy-3,5-diiodo-α-methylbenzylidene)-2-phenylimidazol-5-ones

Some new 1-aryl-4-(4-hydroxy-3,5-diiodo--methylbenzylidene)-2-phenylimidazol-5-ones were prepared by treating the mixture of an analogous 5-oxazolone derivative with aromatic and substituted aromatic amines in the presence of Zeolite (Y-H) catalyst.     

The space of minimal prime ideals in a 0-distributive semilattice

LetS be a 0-distributive semilattice and be its minimal spectrum. It is shown that is Hausdorff. The compactness of has been characterized in several ways. A representation theorem (like Stone's theorem for Boolean algebras) for disjunctive, 0-distributive semilattices is obtained.     

Cyclotridecanone 2,4‐dinitrophenylhydrazone

In cyclotridecanone 2,4‐dinitrophenylhydrazone, C₁₉H₂₈N₄O₄, the 13‐membered carbocycle exists in the triangular [337] conformation. The 2,4‐dinitrophenylhydrazone group is almost perpendicular to the 13‐membered ring, with a dihedral angle of 82.66 (2)° between the mean planes. The dinitrophenylhydrazone rings are packed parallel to each other and separated by 3.28 (1) Å. The NH group forms an intramolecular hydrogen bond to a nitro O atom, and there is a weaker C—H...O interaction between a cyclotridecane CH group and a symmetry‐related 4‐nitro O atom, with a C...O distance of 3.436 (2) Å and a 150° angle about the H atom. The structure, in combination with additional evidence, indicates that [337] is the preferred conformation of cyclotridecane and other simple 13‐membered rings.     

Rate acceleration and subsequent retardation of Diels-Alder reactions in LiClO4-diethyl ether: an experimental investigation.

The experimental kinetic data for several Diels-Alder reactions show why a 5 M LiClO(4)-diethyl ether (LPDE) solution offers maximum enhancement of reaction rates, endo/exo ratios, and yields. These reactions, if carried out in LPDE solutions of concentrations higher than 5 M, show a substantial decrease in these kinetic parameters. This decrease is attributed to the very high viscosity of LPDE solutions near saturation, though this interpretation is not consistent when considered in terms of sizes of the diene and dienophile. The monoetherates, dietherates, and higher other clusters in LPDE solutions and their relationship with the Lewis acid catalysis by Li+ offer a more plausible explanation of both the enhancement and the decrease of the rate of Diels-Alder reactions in this medium.     

New chromogenic reagent for high-performance thin-layer chromatographic detection of organophosphorus insecticide monocrotophos in biological materials

JPC – Journal of Planar Chromatography – Modern TLC -     

Development of experimental heat transfer correlations using Newtonian fluids in helical coils

The experimental work was carried out using water, 10 and 20 % glycerol–water mixture as Newtonian fluids under isothermal and non-isothermal conditions in helical coils. The experiments were performed in laminar and turbulent flow regimes using four helical coils of coil curvature ratios as; δ = 0.055, 0.064, 0.0685 and 0.0757. For the first time, an innovative heat transfer correlations in terms of new dimensionless number ‘M’ are developed based on 135 and 183 tests conducted under isothermal and non-isothermal conditions. The developed heat transfer correlations were compared with the work of earlier investigators and are found to be in good agreement. Hence, M number could be used for characterization of fluid flow in helical coils for any types of fluids which is significant. Also, comparison of Nusselt numbers for water and glycerol–water mixtures under different experimental conditions is presented in this paper. It was observed that as helix diameter increases, Nusselt number decreases due to decrease in centrifugal force.     

Synthesis of sidechain adapted β-turn mimics for modifying the C-terminus of substance P

Sidechain adapted β-turn mimics of type 1 characterised by a fixed cis-conformation of the peptide chain in the aminopiperidinonecarboxylate scaffold have been synthesised from pyrazinones in order to perform a β-turn scan of the messenger region of substance P. The synthesis of a substance P peptide analogue is also described.     

Thermally stimulated luminescence of CaS : Bi : Pd phosphors

CaS phosphors co-activated with Bi⁺³ and Pd⁺² impurities in varying concentrations have been prepared and their thermoluminescence has been systematically studied. The general features of the curves are discussed and the activation energies have been estimated in three different ways. The escape frequency factor is determined using the theoretical model of Randall and Wilkins. Conclusions are drawn regarding the type of kinetics involved in the thermoluminescence process.     

Thermally stimulated luminescence and infrared studies of CaS : Bi,Tm phosphors

Calcium sulphide phosphors doped with bismuth and thulium are prepared from Indian minerals. The glow curves are recorded in the temperature range of 96–320 °K. The activation energies are determined by analyzing the glow peaks after thermal cleaning, using different methods. The results show that, in these phosphors, the electron traps responsible for thermoluminescence are present prior to irradiation. The infrared absorption spectra are recorded in the range of 4000-250 cm^-1. It is concluded that the traps are due to host lattice defects which may arise from S^-2 ion vacancies, created during phosphor preparation.