Bush‐type Hadamard matrices and symmetric designs

Abstact: A symmetric 2‐(100, 45, 20) design is constructed that admits a tactical decomposition into 10 point and block classes of size 10 such that every point is in either 0 or 5 blocks from a given block class, and every block contains either 0 or 5 points from a given point class. This design yields a Bush‐type Hadamard matrix of order 100 that leads to two new infinite classes of symmetric designs with parameters and where m is an arbitrary positive integer. Similarly, a Bush‐type Hadamard matrix of order 36 is constructed and used for the construction of an infinite family of designs with parameters and a second infinite family of designs with parameters where m is any positive integer. © 2000 John Wiley & Sons, Inc. J Combin Designs 9: 72–78, 2001     

P NMR study of the valence stability of tin in its 1-hydroxyethylene-diphosphonate (HEDP) and N,N′,N′-trimethylenephosphonate-polyethyleneimine (PEI-MP) complexes

The valence stability of tin in its complexes with 1-hydroxyethylene-diphosphonate (HEDP) and with N,N′,N′-trimethylenephosphonate-polyethyleneimine (PEI-MP) was investigated. With particular interest in the possible interconversion between Sn²⁺ and Sn⁴⁺, the complexes were monitored with the aid of ³¹P NMR spectroscopy. The extent of complex formation with both ligands was evaluated for systems with tin in their respective oxidation states. The Sn²⁺-complexes underwent initial, but limited oxidation upon preparation, and beyond which were rather stable, irrespective of pH or time. Both Sn²⁺- and Sn⁴⁺-complexes were found to exist in solution without change. Oxidation of Sn²⁺ was achieved by addition of hydrogen-peroxide and was partially reversed by the addition of glutathione (GSH). The amount of H₂O₂ needed for complete oxidation of the Sn²⁺- into Sn⁴⁺-complexes was determined for both ligands, as well as the time taken for that oxidation.     

The relative stability of the tautomers of α-Hydroxytetronic acid

The relative stability of the four tautomeric forms of α-hydroxytetronic acid was calculated with full geometry optimization at the STO -3G , 3–21G , 6–31G *, and 6–31G ** SCF levels. Correlation effects were estimated using the MP 2 method. Intramolecular hydrogen bonds are found to be of primary importance for the relative stability of the various tautomers, and the same tautomer that in the case of L -ascorbic acid is experimentally observed in the crystal as well as in solution is found to be the most stable one, if polarization functions on the hydrogen atoms are taken into account. It is concluded that even in the gas phase this tautomer predominates in α-hydroxytetronic acid as well as in L -ascorbic acid. © 1994 John Wiley & Sons, Inc.     

Poly(alkylene oxide) ionomers. XIII. Copolymers of trioxane with the epoxide and 1,3-dioxolane of methyl 10-undecenoate

Cationic copolymerization of 1,3,5-trioxane with methyl 10,11-epoxyundecanoate or methyl 7,8-epoxyoctanoate and terpolymerization with 1,3-dioxolane was successfully carried out. Co-and terpolymerization of 1,3,5-trioxane with 4-(1-carbomethoxynonyl)-1,3-dioxolane was also achieved. Feed compositions of the functional comonomers were varied from 5 to 40 mol %; in all cases the isolated copolymers contained less than 5% of the functional mer units. The composition of the copolymers showed that the methyl ω-epoxyalkanoates were much less reactive than 1,3,5-trioxane. A similar trend was observed with the functional dioxolane monomer, although significantly shorter induction periods were observed in comparison with the epoxy/trioxane copolymerizations. The oxymethylene copolymers and terpolymers were characterized primarily by their infrared spectra; however, the thermal and base stabilities of selected copolymers were also determined.     

Improvements in graphite-furnace atomic-absoption microanalysis with solid sampling

Summary Microanalysis using mechanized solid sampling with graphite-furnace atomic-absorption gives accurate results in the determination of trace elements in different NBS Standard Reference Materials. Analytical conditions are optimized by use of the method of standard additions, and all capabilities of a microcomputer controlled graphite furnace, such as matrix modification by oxygen ashing, temperature ramping and maximum power heating for atomization are used. Direct calibration against acid standards is possible.

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Verbesserung der Atomabsorptions-Mikroanalyse fester Proben im Graphitrohrofen

Zusammenfassung Die Mikroanalyse von Spurenelementen in verschiedenen NBS Standard-Referenzmaterialien unter Zuhilfenahme eines mechanisierten Zubehörs zur Festprobendosierung ergibt genaue Ergebnisse. Die Optimierung der analytischen Bedingungen wurde mit der Additionsmethode überprüft, wobei alle Möglichkeiten eines modernen mikrocomputer-gesteuerten Graphitrohrofens, wie Matrixmodifikation durch Sauerstoffveraschung, kontrollierter Temperaturanstieg und Atomisierung mit der superschnellen Heizrate ausgeschöpft wurden. Die direkte Messung gegen angesäuerte Bezugslösungen ist möglich.

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Presented at the 8th International Microchemical Symposium, Graz, August 25–30, 1980.     

A novel approach in analyzing aromaticity by homo- and isostructural reactions: an ab initio study of fluorobenzenes

The influence of fluorine substitutions on the stability of benzene is examined by using the Hartree-Fock (HF) and MP2 models. It is conclusively demonstrated that homodesmotic reactions based on the open-chain zigzag polyenes are unsatisfactory. A comparison of the intramolecular interactions of educts and products shows that they are not well balanced. Hence, these reactions should be abandoned in discussing aromaticity. A much better vehicle for exploring aromaticity is provided by homostructural reactions, which employ cyclic monoene and diene as reference model compounds. Their heavy atoms are enforced to assume planar geometries to enable sigma/pi separation. The HF/cc-pVTZ calculations show that extrinsic aromaticity of benzene B DeltaE(ease)(B)() arises both from the sigma- and pi-contributions. They are -14.8 and -23.1 in kcal/mol, respectively, if the stockholder energy partitioning scheme is employed. This result implies that both the sigma- and pi-frameworks contribute to the aromatic stabilization of B, the latter being more important. The total aromatic stabilization DeltaE(ease)(B)() is -37.9 kcal/mol. Schleyer's indene-isoindene isomerization approach also strongly indicates that the decisive factor in determining the aromatic stability of the benzene moiety is the pi-electron framework. The origin of extrinsic aromaticity is identified as the increased nuclear-electron attraction of both sigma- and pi-electrons, if 1,3-cyclohexadiene is used as a gauge compound. Further, by using a system of isostructural reactions, it is conclusively demonstrated that fluorobenzenes exhibit a remarkable additivity of the substituent effects, as far as the stability of multiply substituted benzenes is concerned. This additivity rule is so accurate that it enables delineation of the fluorine repulsions and the aromaticity defect DeltaE(AD). It appears that the DeltaE(AD) values increase upon sequential fluorine substitution at the next nearest (vicinal) position thus making multiply fluorinated benzenes less stable.     

Finite 2-groups all of whose nonmetacyclic subgroups are generated by involutions

We classify here nonmetacyclic finite 2-groups all of whose nonmetacyclic subgroups are generated by involutions (Theorem 1.1). This solves problem Nr. 710 for p = 2 stated by Y. Berkovich in [1]. For p > 2 the corresponding problem is open. Received: 14 March 2007 Revised: 15 April 2007