In quest of strong neutral organic bases and superbases—supramolecular systems containing four pyridine subunits

It is shown by a reliable DFT method that supramolecular structures 1 and 2, constructed using pyridine as an essential building block, act as powerful neutral organic superbases in the gas phase and in acetonitrile due to cationic resonance and hydrogen bonding in the conjugate acids amplified by the NMe₂ groups placed at strategic positions on the molecular backbone.     

Finite nonabelian p-groups all of whose nonabelian maximal subgroups are either metacyclic or minimal nonabelian

We give here a complete classification of the title groups (Theorem A).     

A block algorithm for computing antitriangular factorizations of symmetric matrices

Any symmetric matrix can be reduced to antitriangular form in finitely many steps by orthogonal similarity transformations. This form reveals the inertia of the matrix and has found applications in, e.g., model predictive control and constraint preconditioning. Originally proposed by Mastronardi and Van Dooren, the existing algorithm for performing the reduction to antitriangular form is primarily based on Householder reflectors and Givens rotations. The poor memory access pattern of these operations implies that the performance of the algorithm is bound by the memory bandwidth. In this work, we develop a block algorithm that performs all operations almost entirely in terms of level 3 BLAS operations, which feature a more favorable memory access pattern and lead to better performance. These performance gains are confirmed by numerical experiments that cover a wide range of different inertia.     

The high affinity of azacalix[3](2,6)pyridine derivatives for Be cations—a DFT study

It is shown using a reliable DFT method that N,N′,N″-tris(phenyl)azacalix[3](2,6)pyridine derivatives act as powerful sequestering agents for Be²⁺ cations in the gas phase and in acetonitrile solution due to cationic resonance and strong beryllium bonding in the complexes.     

Copolymerization and copolymers of brominated phenylmaleimides with some vinyl monomers

The kinetics of the free radical copolymerization in solution of N-(4-bromophenyl)maleimide (MBPMI), N-(2, 4-dibromophenyl)maleimide (DBPMI) and N-(2, 4, 6-tribromophenyl)maleimide (TBPMI) with styrene (St), methyl acrylate (MA), methyl methacrylate (MMA) and acrylonitrile (AN) at low and high conversions were described. Some characteristic properties of the copolymers obtained, particularly their thermal behaviour were also presented.     

Thermal and flammability behaviour of copolymers of N-(2, 4, 6-tribromophenyl)maleimide with some acrylates

The copolymers of N-(2, 4, 6-tribromophenyl)maleimide (TBPMI) with methyl acrylate, methyl methacrylate and acrylonitrile of different composition were prepared by free radical polymerization at low conversion. Their thermal behaviour was established by TGA measurements in helium atmosphere and flammability properties were determined by limiting oxygen index method. The higher TBPMI content in the copolymer led to a higher thermal stability and lower flammability particularly when Sb₂O₃ was used as a synergist.     

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.