Antibonding orbitals and their role in electronic interactions in compounds with a phosphoryl group

A simple qualitative model of hyperconjugation interactions, which can be used in the examination of questions concerning conjugation in phosphorus compounds, has been proposed. The model makes it possible to predict the magnitude and direction of conjugation effects on a qualitative level on the basis of the electronegativities of the atoms forming a bond and their valence state. The direction of a hyperconjugation effect can be evaluated in a first approximation on the basis: of the magnitude of the contributions of the atomic orbital of the central atom to the bonding and antibonding orbitals of the bonds. The magnitude of the effect depends on the relative orientation of the donor and acceptor orbitals, i.e., on the conformation of the molecules. The bonding in the phosphoryl group has been examined in the framework of the proposed model to evaluate the influence of the structure of the molecule on the magnitude of the hyperconjugation interactions. The bond in the phosphoryl group of an X₃P=O molecule has been interpreted as the result of the n,^* conjugation of the lone pairs of the phosphoryl oxygen with the p-^x* orbitals. The influence of the induction and resonance effects of the substituents on the phosphorus atom, as well as their conformation and the angular stresses, on the multiplicity of the bonds in the phosphoryl group has been considered in the framework of the proposed model.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 21, No. 1, pp. 39–45, January–February, 1985.     

Mass spectra of some high molecular weight tetra(alkyl)silanes

The mass spectra of tetra(alkyl)silanes having one short and three long alkyl groups were recorded (C₂₀? C₃₂). These silanes did not give molecular ions, and the dominant course of fragmentation involved the loss of alkyl groups, followed by elimination of alkenes. The loss of alkyl groups, followed by elimination of alkenes. The loss of alkyl groups followed the sequence iso-Pr>Et, Pr,… C₁₄H₂₉» Me. With alkyl groups longer than hexyl, a rearrangement was observed in which n-alkanes were eliminated from the base ion. When the alkyl group was hexyl, the alkane eliminated was methane; when the alkyl group was heptyl, ethane was expelled; with octyl, it was propane; and with decyl, n-pentane was expelled. Deuterium labeling showed that at least two modes of rearrangement were occurring.     

Method of Best Successive Approximations for Nonlinear Operators

We present a new approach to the approximation of nonlinear operators in probability spaces. The approach is based on a combination of the specific iterative procedure and the best approximation problem solution with a quadratic approximant. We show that the combination of these new techniques allow us to build a computationally efficient and flexible method. The algorithm of the method and its application to the optimal filtering of stochastic signals are given.     

Surface patterning of silica nanostructures using bio-inspired templates and directed synthesis

Natural systems excel in directing the synthesis of inorganic materials for various functional purposes. One of the best-studied systems is silica synthesis, as occurs in diatoms and marine sponges. Various biological and synthetic polymers have been shown to template and catalyze silica formation from silicic acid precursors. Here, we describe the use of poly-L-lysine to promote the synthesis of silica in neutral, aqueous solution and when immobilized onto a silicon support structure under similar conditions. Either reagent jetting or conventional photolithography techniques can be used to pattern the templating polymer. Spots created by reagent jetting led to the creation of silica structures in the shape of a ring that may be a result of the spotting process. Photolithographically defined poly-L-lysine spots led to thin laminate structures after exposure to a dilute aqueous silicic acid solution. The laminate structures were nanostructured and highly interconnected. Photolithographic patterning of (3-aminopropyl)trimethoxysilane, a reagent that mimics the lysine functional group, led to similar silica coatings even though low-molecular-weight materials do not rapidly promote silica synthesis in solution. This result highlights the importance of functional-group arrangement for templating and promoting the synthesis of inorganic materials. The described surface-patterning techniques offer a route to integrate conventional silicon-patterning technologies with biologically based material synthesis. Such combined fabrication techniques enable controlled assembly over multiple length scales and an approach to understanding interfacial silica synthesis, as occurs in natural systems.     

Synthesis and molecular structure of solvated hydride complexes of aluminium and di-η5-cyclopentadienylyttrium

A series of hydride complexes of di-η⁵-cyclopentadienyl-yttrium and -aluminium solvated by a Lewis base, viz. Cp₂YAlH₄NEt₃ (I), Cp₂YAlH₄THF (II), Cp₂YAlH₄OEt₂ (III) and (Cp₂YAlH₄)₂OEt₂ (IV), (Cp = η⁵-cyclopentadienyl) was synthesized. An X-ray study of compounds I and IV was performed, yielding the coordinates of the heavy atoms. The positions of the hydrogen atoms were determined accordingly from the IR data and also by comparison with the analogous hydridohalide complexes (Cp₂YCl)₂AlH₃L. The structures of I and IV may be represented by the following formulae: [(η⁵-C₅H₅)₂Y(μ₃-H)AlH₂NEt₃]₂ (I) and {[(η⁵-C₅H₅)₂Y]₂(μ₃-H)}[(μ₂-H)₂AlH₂][(μ₂-H)₂AlHOEt₂] (IV).     

Dimerization of iminophosphoryl compounds and electrophilicity of the antibonding oribitals of the phosphorus atom

The capacity of compounds containing the iminophosphoryl group for dimerization has been considered in the framework of a previously proposed qualitative model of the dependence of the electrophilicity of antibonding orbitals on the structure of molecules. Dimerization involves the attack of the lone pair of the nitrogen atom on the most electrophilic ^* orbital of another molecule of the iminophosphoryl compound. In contrast to the existing theories, it follows from the present treatment that the replacement of one or two groupings on the phosphorus atom by groupings with stronger electron-donor properties should not have a significant influence on the capacity of a molecule for dimerization.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 21, No. 5, pp. 536–543, September–October, 1985.