Graph-theoretical analysis of the clar's aromatic sextet : Mathematical properties of the set of the kekulé patterns and the sextet polynomial for polycyclic aromatic hydrocarbons

The mathematical structure of a set of the Kekulé patterns for a polycyclic aromatic hydrocarbon has been analysed graph-theoretically. By defining the proper and improper sextets, sextet pattern, Clar transformation, and sextet rotation, one can prove the important property of the sextet polynomial B_G(x) as B_G(1) = K(G), where K(G) is the number of the Kekulé patterns for thin polyhex graph G. For fat polyhex graphs such as coronene the above relation is found to be also valid by introducing the concept of a super sextet. All the Kekule patterns for a given G are shown to form a hierarchical tree structure by the sextet rotation. The theory developed in this paper gives a mathematical basis and interpretation for the concept of the Clar's aromatic sextet.     

Novel use of organotin halide-base complex in organic synthesis. Cycloaddition reaction of oxetane with isocyanates.

Cycloadditions of oxetanes with isocyanates were markedly accelerated by the complex of Bu₂SnI2 and Ph₃P=O which could be readily handled and hardly caused a trimerization of isocyanates, yielding oxazin-2-ones under neutral and mild reaction conditions.     

On the calculation of the acyclic polynomial

Graphical methods are developed for recursive evaluation of the acyclic polynomial. Analytical formulas of the acyclic polynomials for several specific series of graphs are given. Mathematical properties of the derivatives of the acyclic polynomial are given.     

β-Methallylrhodium(III) supported on a vanadium oxide cluster: Synthesis,structure, and reaction

Reaction of [(³-C₄H₇)₂Rh(CH₃CN)₂]PF₆(³-C₄H₇ = -methallyl) with [n-Bu₄N](VO₃) gives a new ³-allyl cluster [n-Bu₄N]₂[{(³-C₄H₇)₂Rh}₂ (V₄O₁₂)] (I) which is readily converted into a diene cluster, [n-Bu₄N]₂ [{(⁴-C₈H₁₄)Rh}₂(V₄O₁₂)] (II) (C₈H₁₄=2,5-dimethyl-1,5-hexadiene) by reacting with CO or P(OEt)₃;I andII have been characterized crystallographically.     

Synthesis of amphiphilic particles in the presence of inert solvents and their application to lipase immobilization

To develop monodisperse amphiphilic polymer particles on which a large amount of lipase could be immobilized, we performed seed polymerizations of glycidyl methacrylate and allyl methacrylate in the presence of nonpolar inert and polar inert solvents. The amphiphilic porous polymer particles, which had both hydrophilic guanidino groups and hydrophobic stearoyl groups, were synthesized in the presence of n‐decane and had a large amount of macropores with diameters of 50–1000 nm. The amount of lipase immobilized on the amphiphilic particles synthesized in the presence of n‐decane was 3.85 times that of the lipase immobilized on the amphiphilic particles synthesized in the absence of a solvent. The immobilized lipase prepared with the amphiphilic particles synthesized in the presence of n‐decane exhibited a high transesterification activity in n‐hexane and could be used repeatedly without a considerable activity loss. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 874–884, 2002; DOI 10.1002/pola.10178     

Synthesis of allyl cyanamides and N-cyanoindoles via the palladium-catalyzed three-component coupling reaction

The palladium-catalyzed three-component coupling reaction (TCCR) of aryl isocyanides, allyl methyl carbonate, and trimethylsilyl azide was conducted in the presence of Pd(2)(dba)(3).CHCl(3) (2.5 mol %) and dppe (1,2-bis(diphenylphosphino)ethane) (10 mol %). Allyl aryl cyanamides with a wide variety of functional groups were obtained in excellent yields. This palladium-catalyzed TCCR was further utilized for the synthesis of N-cyanoindoles. The reaction of 2-alkynylisocyanobenzenes, allyl methyl carbonate, and trimethylsilyl azide in the presence of Pd(2)(dba)(3).CHCl(3) (2.5 mol %) and tri(2-furyl)phosphine (10 mol %) at higher temperatures afforded N-cyanoindoles in good to allowable yields. (eta(3)-Allyl)(eta(3)-cyanamido)palladium complex, an analogue of the bis-pi-allylpalladium complex, is a key intermediate in the TCCR, and a pi-allylpalladium mimic of the Curtius rearrangement is involved to generate the (eta(3)-allyl)(eta(3)-cyanamido)palladium intermediate.     

Photoionization cross section calculated by dynamical theory

A new theoretical method to calculate the photoionization cross sections of complex molecules and solids is derived in the framework of the dynamical theory by using the Green's function method. The approximations applicable to treat the photoionization by x-rays are also discussed.     

The structure of a new antibiotic,chromoxymycin

Based on ¹H- and ¹³C-NMR spectral data, the planar structure of chromoxymycin, a new antitumor antibiotic, has been determined as shown in Fig. 1.     

Diversity of the biosynthesis of the isoprene units

This review covers the biosynthesis of the starter units of terpenoids, isopentenyl diphosphate (IPP) and dimethylallyl diphosphate (DMAPP) via the nonmevalonate pathway together with a new enzyme involved in the conversion of IPP and DMAPP, i.e type 2 IPP isomerase. The biosynthesis of terpenoids produced by actinomycetes is also reviewed. 117 references are cited.     

Mass spectra of pyridazines and their N-oxides

The mass spectra of pyridazines and their N-oxides is reported. Previous electron impact studies on aromatic amine N-oxides reported the appearance of M-16 and/or M-17 ion peaks as the usual feature of the fragmentations. In our experiments, the representative fragmentation of the pyridazine N-oxides involves formation of a M-30 (M-NO) ion. The fragmentation patterns substantiated by extensive high resolution studies and the analysis of the appropriate metastable ions.