Ab initio MO Calculations of benzene + TCNE and naphthalene + TCNE complexes with STO-3G π-split basis set

Ab initio SCF MO calculations have been carried out on benzene + TCNE (tetracyanoethylene) and naphthalene + TCNE complexes with the STO -3G, STO -3G π-split (STO -3G for π orbitals and a split basis for π orbitals), and 4–31G basis sets. The interaction energy, gross charges, dipole moment, and the electron density in the middle plane of the complexes have also been evaluated. The STO -3G π-split basis set is appropriate for the calculation of large π–π stacking complexes from two points of view, production of reliable results and ease of computations. The approximation scheme based on the semiorthogonalized orgitals is revealed to be very efficient to save CPU time and storage in such calculations. The stable conformation and the charge-transfer interaction of the two complexes are discussed on the basis of the calculated quantities.     

BINAP/AgOTf/KF/18-crown-6 as new bifunctional catalysts for asymmetric Sakurai-Hosomi allylation and Mukaiyama aldol reaction

A catalytic amount of KF.18-crown-6 complex is effective as a soluble fluoride source to activate an asymmetric Sakurai-Hosomi allylation with BINAP and silver(I) triflate catalyst. The allylation of a variety of aromatic, alpha,beta-unsaturated and aliphatic aldehydes with allylic trimethoxysilane resulted in high yields and remarkable enantioselectivities. In addition, the asymmetric Mukaiyama-type aldol reaction is achieved by using trimethoxysilyl enol ethers in the presence of the same catalysts. High anti selectivity is obtained from E-silyl enol ether, while Z-silyl enol ether gives syn selectivity.     

New method for the determination of pentachlorophenol by atomic absorption spectrophotometry

A new application of atomic absorption is reported for the determination of pentachlorophenol. The method is based on solvent extraction into nitrobenzene of the ion-pair formed between tris(1,10-phenanthroline) iron(II) and the anion of pentachlorophenol, and the subsequent determination of the iron concentration m the extract by atomic absorption at the 2483 A iron line.     

Synthesis of 2-alkylidenetetrahydrofurans by Ru-catalyzed regio- and stereoselective codimerization of dihydrofurans with alpha,beta-unsaturated esters

2-(1-Alkoxycarbonyl)alkylidenetetrahydrofurans were readily synthesized by the codimerization of 2,3- or 2,5-dihydrofurans with alpha,beta-unsaturated esters using a zerovalent Ru catalyst, Ru(cod)(cot), with high regio- and stereoselectivity.     

A novel boron-rich quaternary scandium borocarbosilicide Sc3.67−xB41.4−y−zC0.67+zSi0.33−w

A novel quaternary scandium borocarbosilicide Sc_3.67−xB_41.4−y−zC_0.67+zSi_0.33−w was found. Single crystallites were obtained as an intergrowth phase in the float-zoned single crystal of Sc_0.83−xB_10.0−yC_0.17+ySi_0.083−z that has a face-centered cubic crystal structure. Single crystal structure analysis revealed that the compound has a hexagonal structure with lattice constants a = b = 1.43055(8) nm and c = 2.37477(13) nm and space group (No. 187). The crystal composition calculated from the structure analysis for the crystal with x = 0.52, y = 1.42, z = 1.17, and w = 0.02 was ScB_12.3C_0.58Si_0.10 and that agreed rather well with the composition of ScB_11.5C_0.61Si_0.04 measured by EPMA. In the crystal structure that is a new structure type of boron-rich borides, there are 79 structurally independent atomic sites, 69 boron and/or carbon sites, two silicon sites and eight scandium sites. Boron and carbon form seven structurally independent B₁₂ icosahedra, one B₉ polyhedron, one B₁₀ polyhedron, one irregularly shaped B₁₆ polyhedron in which only 10.7 boron atoms are available because of partial occupancies and 10 bridging sites. All polyhedron units and bridging site atoms interconnect each other forming a three-dimensional boron framework structure. Sc atoms reside in the open spaces in the boron framework structure.     

Lewis acid-activated chiral leaving group: enantioselective electrophilic addition to prochiral olefins

A new strategy using a BINOL derivative as a chiral leaving group and Lewis acid has been developed for enantioselective alkylation of prochiral olefins. (R)-2,2'-Bis[2-(trimethylsilyl)ethoxymethyl]-1,1'-binaphthol is demonstrated to be an effective reagent for enantioselective hydroxymethylation of silyl enol ethers and trisubstituted alkenes. Electrophilic addition to prochiral olefins is accompanied by cleavage of an acetal that is dual activated by SnCl4 and the delta-effect of silicon through the S(N)2 substitution process. Enantioselective synthesis of cyclic terpenes is also described using this strategy.     

Polyesters containing ring units in main chains. I. Preparation and stereochemistry of monomers and polyesters

Cycloalkanone (C₅–C₈, C₁₂, and C₁₅) or cycloalkane (C₅ and C₆) ring-containing monomeric diesters and the polyesters derived from them were prepared, and their configurations were studied by ¹³C-NMR spectroscopy. Absolute configurations were determined for ring sizes 5, 6, and 7. Configurational change during reduction of a ketonic group of monomeric diesters with ring sizes 5 and 6 was discussed in terms of the steric effect of ring substituents on the ketonic group. In the polycondensation reaction epimerization of the ring units was observed in 5-, 6-, and 7-membered cycloalkanones and not in others, which is explained by steric hindrance by the ring substituents against attack of tetrabutyl titanate catalyst on the ketonic group.     

Polymerization of acrylamide initiated with pinacol–ceric ion redox system

Polymerization of acrylamide initiated with a pinacol–ceric ion redox system was investigated. The polymer obtained was found to contain one cerium atom in a polymer molecule. It was considered that the cerium atom was introduced into the polymer molecule by the termination reaction as there is no cerium atom in the initiating radical in the present system. A similar termination reaction was attained by ferric ion but not by cerous ion. The metal ion was considered to terminate the polymerization to form a stable polymer. Some considerations on the structure of the reaction product relating to the polymerization mechanism were discussed.     

Structural analysis of amylose tris(3,5-dimethylphenylcarbamate) by NMR relevant to its chiral recognition mechanism in HPLC

The structural analysis of amylose tris(3,5-dimethylphenylcarbamate) (ADMPC) was performed by NMR spectroscopy using a sample with a lower degree of polymerization in order to understand the chiral recognition mechanism when it was used as a chiral stationary phase (CSP) in high-performance liquid chromatography (HPLC). ADMPC exhibited chiral discrimination for many enantiomers, including 1-(9-anthryl)-2,2,2-trifluoroethanol (1) and 1,1'-bi-2-naphthol (2) in both NMR and HPLC. A good agreement was observed between the HPLC and NMR results when chloroform was employed as the common solvent. The structure of ADMPC in solution was investigated by NMR using the 2D NOESY technique coupled with computer modeling, and a left-handed 4/3 helical structure was obtained as the most probable one. The binding geometry between ADMPC and the enantiomers of 1 was also investigated by (1)H NMR titration. On the basis of these results combined with molecular modeling, a rational model to explain the chiral discrimination mechanism of 1 on ADMPC was proposed.     

Dissociation equilibrium between uncharged and charged local anesthetic lidocaine in a surface-adsorbed film

The dissociation equilibrium between uncharged local anesthetic lidocaine (LC) and charged local anesthetic LC (LCH⁺) in a surface-adsorbed film was investigated by measuring the surface tension and pH of aqueous solutions of a mixture of hydrochloric acid and LC. The surface tension values decreased slightly with increasing total molality m_t at 0X₂0.5, where X₂ is the mole fraction of LC in the mixture, while they decreased rapidly with increasing m_t at 0.5<X₂1. It was shown from the pH measurements that almost all LC molecules were changed into LCH⁺ ions by protonation at 0X₂0.5 and both forms coexisted only at 0.5<X₂1. The quantities of the respective LC and LCH⁺ transferred from the aqueous solution to the adsorbed film, i.e., their surface densities, were calculated by applying the thermodynamic equations derived to the surface tension and pH data. A greater quantity of LC than LCH⁺ existed in the adsorbed film at the coexisting composition. The partitioning behavior of LC and LCH⁺ in the adsorbed film was characterized by three composition regions: (1) slight partitioning of low surface-active LCH⁺ in the region at 0X₂0.5, (2) preferential partitioning of LC at 0.5<X₂<around 0.7, and (3) negative partitioning of LCH⁺ at around 0.7X₂1. The present results clearly indicate that uncharged local anesthetics transfer into hydrophobic environments such as cell membranes more than charged ones.