Sulfures et disulfures : acidités cinétiques relatives des protons adjacents au soufre

Dibenzyl disulfide is deprotonated at ?78° approximately 7.5 times more rapidly than dibenzyl sulfide, as predicted by a molecular orbital analysis which focuses on the interaction between the carbon lone pair and an adjacent σ * orbital.     

A relationship between correlation energies and sizes: The helium-like ions

The correlation energy (E _corr) is found to be inversely proportional to the product of the electron pair size (2>) and the square of the effective nuclear charge (Z _eff) for the helium-like ions.     

Local structure and thermodynamics of a core-softened potential fluid: theory and simulation.

Phase behavior and structural properties of homogeneous and inhomogeneous core-softened (CS) fluid consisting of particles interacting via the potential, which combines the hard-core repulsion and double attractive well interaction, are investigated. The vapour-liquid coexistence curves and critical points for various interaction ranges of the potential are determined by discrete molecular dynamics simulations to provide guidance for the choice of the bulk density and potential parameters for the study of homogeneous and inhomogeneous structures. Spatial correlations in the homogeneous CS system are studied by the Ornstein-Zernike integral equation in combination with the modified hypernetted chain (MHNC) approximation. The local structure of CS fluid subjected to diverse external fields maintaining the equilibrium with the bulk CS fluid are studied on the basis of a recently proposed third order+second order perturbation density functional approximation (DFA). The accuracy of DFA predictions is tested against the results of a grand canonical ensemble Monte Carlo simulation. Reasonable agreement between the results of both methods proves that the DFA theory applied in this work is a convenient theoretical tool for the investigation of the CS fluid, which is practically applicable for modeling numerous real systems.     

Synthesis and Diels-Alder Reactions of a New Kind of Chiral Dienophiles: Cyclic Vinyl-p-tolylsulfilimines

A new kind of chiral dienophiles, cyclic vinyl-p-tolylsulfilimines (2a and 2b), were obtained from the corresponding (Z)-sulfinylacrylonitriles with HBF(4) and methanol. The asymmetric Diels-Alder reaction of optically pure 2a with cyclopentadiene under mild thermal or catalyzed conditions afforded only the endo-4a adduct with complete endo and pi-facial selectivities. The ability of the sulfilimine moiety to enhance the dienophilic reactivity of the double bond is similar to that of the sulfinyl group.     

N-methyl-substituted aromatic polyamides

A series of N-methyl-substituted aromatic polyamides derived from the secondary aromatic diamines 4,4′-bis(methylamino)diphenylmethane, 3,3′-bis(methylamino)diphenylmethane, 4,4′-bis(methylamino)benzophenone or 3,3′-bis(methylamino)benzophenone and isophthaloyl dichloride, and terephthaloyl dichloride or 3,3′-diphenylmethane dicarboxylic acid dichloride was prepared by high-temperature solution polymerization in s-tetrachloroethane. Compared with analogous unsubstituted and partly N-methylated aromatic polyamides, the full N-methylated polyamides exhibited significantly lower glass transition temperatures (T_g), reduced crystallinity, improved thermal stability, and good solubility in chlorinated solvents.     

Acid–base complexes of polymers

The physical interactions of polymers with neighboring molecules are determined by only two kinds of interactions: London dispersion forces and Lewis acid–base interactions. These two kinds of attractive energies (together with certain steric restrictions) determine solubility, solvent retention, plasticizer action, wettability, adsorption, adhesion, reinforcement, crystallinity, and mechanical properties. The London dispersion force interaction energies of polymers have been quantified by the dispersion force contribution to cohesive energy density (δ²_d) and the dispersion force contribution to surface energy (δ^d). The Lewis acid–base interactions, often referred to as “polar” interactions, can be best quantified by Drago's C_A and E_A constants for acid sites and C_B and E_B constants for basic sites. In this article infrared spectral shifts are featured as a method of determining enthalpies of acid–base interaction, and the C and E constants for polymers, plasticizers, and solvents. Examples are given where acid–base complexation of polymers with solvents dominate solubility and swelling phenomena. Enthalpies of acid–base complexation in polymer blends are determined from spectral shifts.     

An ADMET route to unsaturated polyacetals

The successful acyclic diene metathesis polymerization (ADMET) of an α,ω-diene containing an acetal moiety is presented. A linear, unsaturated polyacetal is produced with a number average molecular weight of 23000 as determined by gel permeation chromatography (GPC). Thermogravimetric analysis (TGA) of the polymer reveals onsets of decomposition below 300°C in both air and nitrogen atmospheres while differential scanning calorimetry (DSC) indicates that the polymer is primarily amorphous.     

A Highly Active Catalyst for the Room-Temperature Amination and Suzuki Coupling of Aryl Chlorides

A unique combination of steric and electronic properties appears to determine the effectiveness of phosphanyl-substituted biphenyls as ligands in palladium-catalyzed aminations and Suzuki coupling of aryl chlorides at room temperature [Eq. (1)]. The oxidative addition step is greatly accelerated, and transmetalation (or Pd−N bond formation) and reductive elimination processes are facilitated. Use of these ligands allows for Suzuki coupling at very low catalyst loadings (as little as 10⁻⁶ mol % Pd). R″=cyclohexyl, tert-butyl.