DFT and CASPT2 study of two thermal reactions of nitromethane: C–N bond cleavage and nitro-to-nitrite isomerization. An example of the inverse symmetry breaking deficiency in density functional calculations of an homolytic dissociation

The reaction paths of nitromethane leading to the dissociation products or isomerization to methyl nitrite have been computationally investigated at the CAS-SCF and DFT levels of theory. Additionally, the CAS-SCF wave functions were used as reference in a second-order perturbation treatment, CASPT2, in order to obtain a good estimate for the activation energy of each reaction path. Both methods predict the isomerization as a concerted reaction. However, the behavior of the two approximations with respect to dissociation is rather different; while CASPT2 predicts a barrier height of (≈59 kcal/mol) in good accordance with the experimental activation energy (59.0 kcal/mol), B3-LYP/6-31G^* calculations overestimate the barrier for more than 30 kcal/mol. The DFT prediction of the dissociation channel exhibits inverse symmetry breaking, dissociating to the unphysical absurd CH₃^δ+ plus NO₂^δ−.     

Solution Equilibria of Ternary Systems Involving Nickel(II) Ion,Picolinic Acid,and the Amino Acids Histidine,Cysteine, Aspartic and Glutamic Acids

Solution equilibria of the ternary systems Ni(II)–picolinic acid (Hpic) and the amino acids aspartic acid (H₂asp), glutamic acid (H₂glu), cysteine (H₂cys) and histidine (Hhis), where the amino acids are denoted as H _i L, have been studied pH-metrically. The formation constants of the resulting mixed ligand complexes have been determined at 25 °C using a ionic strength 1.0 mol·dm^?3 NaCl. In the Ni(II)–Hpic–H₂asp and Ni(II)–Hpic–H₂glu systems, the complexes [Ni(pic)H₂L]⁺, Ni(pic)HL, [Ni(pic)L]^? and [Ni(pic)L(OH)]^2? were detected. In the Ni(II)–Hpic–H₂cys system the complexes [Ni(pic)H₂L]⁺ and [Ni(pic)L]^? are present. Additionally, in the Ni(II)–Hpic–Hhis system the species [Ni(Hpic)HL]²⁺, Ni(pic)L and [Ni(pic)L(OH)]^? were identified. The species distribution diagrams as functions of pH are briefly discussed.     

Supported carbon molecular sieve membranes based on a phenolic resin

The preparation of a composite carbon membrane for separation of gas mixtures is described. The membrane is formed by a thin microporous carbon layer (thickness, 2 μm) obtained by pyrolysis of a phenolic resin film supported over a macroporous carbon substrate (pore size, 1 μm; porosity, 30%). The microporous carbon layer exhibits molecular sieving properties and it allows the separation of gases depending on their molecular size. The micropore size was estimated to be around 4.2 Å. Single and mixed gas permeation experiments were performed at different temperatures between 25°C and 150°C, and pressures between 1 and 3.5 bar. The carbon membrane shows high selectivities for the separation of permanent gases like O₂/N₂ system (selectivity≈10 at 25°C). Gas mixtures like CO₂/N₂ and CO₂/CH₄ are successfully separated by means of prepared membranes. For example, the membrane prepared by carbonization at 700°C shows at 25°C the following separation factors: CO₂/N₂≈45 and CO₂/CH₄≈160.     

Entropic measures of Rydberg‐like harmonic states

The Shannon entropy, the desequilibrium and their generalizations (Rényi and Tsallis entropies) of the three‐dimensional single‐particle systems in a spherically symmetric potential V(r) can be decomposed into angular and radial parts. The radial part depends on the analytical form of the potential, but the angular part does not. In this article, we first calculate the angular entropy of any central potential by means of two analytical procedures. Then, we explicitly find the dominant term of the radial entropy for the highly energetic (i.e., Rydberg) stationary states of the oscillator‐like systems. The angular and radial contributions to these entropic measures are analytically expressed in terms of the quantum numbers which characterize the corresponding quantum states and, for the radial part, the oscillator strength. In the latter case, we use some recent powerful results of the information theory of the Laguerre polynomials and spherical harmonics which control the oscillator‐like wavefunctions.