AM1 Computed Vibrations in Two C60O Structures

Harmonic vibrational analysis for fully optimized C_s and C_2v structures of C₆₀O has been performed with AM1 quantum-chemical method. The vibrational frequencies, their (partial) symmetry classification and IR intensities are reported, and their relationships to observations discussed.     

Comment on Formulating and Generalizing Dirac's, Proca's, and Maxwell's Equations with Biquaternions or Clifford Numbers

Many difficulties of interpretation met by contemporary researchers attempting to recast or generalize Dirac's, Proca's, or Maxwell's theories using biquaternions or Clifford numbers have been encountered long ago by a number of physicists including Lanczos, Proca, and Einstien. In the modern approach initiated by Gürsey, these difficulties are solved by recognizing that most generalizations lead to theories describing superpositions of particles of different intrinsic spin and isospin, so that the correct interpretation emerges from the requirement of full Poincaré covariance, including space and time reversal, as well as reversion and gauge invariance. For instance, the doubling of the number of solutions implied by the simplest generalization of Dirac's equation (i.e., Lanczos's equation) can be interpreted as isospin. In this approach, biquaternions and Clifford numbers become powerful opportunities to formulate the Standard Model of elementary particles, as well as many of its possible generalizations, in very elegant and compact ways.     

On simple double zeros and badly conditioned zeros of analytic functions of variables

We give a numerical criterion for a badly conditioned zero of a system of analytic equations to be part of a cluster of two zeros.

     

Characterizations of Thermoplastic Block Elastomers Based on Polybutadiene and ε -Caprolactone

A broad series of tri- and multiblock copolymers based on linear and branched oligomers of polybutadiene as central blocks and polycaprolactone (PCL) as block extremities are characterized by SEC, DSC, DMA, Dynamical Rheology and DRX. DSC analyses reveal phase separation between the two amorphous PB and PCL phases. By thermal analysis, the glass transition temperature of PCL is only detected for materials containing at least 80% w/w of PCL. This is attributed to the small length of the polyester blocks for copolymers containing less than 80% w/w of PCL. The increase of fusion heat with increasing PCL content in the copolymers is correlated to the greater ability of PCL chains to rearrange as HTPB amount decrease in the material. Regarding the evolution of the melting temperature of the various copolymers, the characterization by DMA and dynamical rheology confirms the behaviour observed by DSC. Mechanical and rheological properties (i.e., storage modulus and complex viscosities) were studied and reveal that the behavior of the copolymers depends on both the rate of PCL chains and on the nature of the elastomeric block.     

Zirconium Promoted Ring Opening. A New Route to Phosphinites and Polyphosphinites

Abstract

Ring opening reactions involving various heterocycles, the Schwartz reagent [Cp₂ZrHC1]_n and a number of chlorophosphines or phosphenium salts will be presented. Scope and limitations of this useful methodology will be discussed.     

Studies on The Application of The Paternò-Büchi Reaction to The Synthesis of Novel Fluorinated Scaffolds

In the context of new scaffolds obtained by photochemical reactions, Paternò-Büchi reactions between heteroaromatic, trifluoromethylphenyl ketone and electron rich alkenes to give oxetanes are described. A comprehensive study has then been carried out on the reaction of aromatic ketones with fluorinated alkenes. Depending on the substitution pattern at the oxetane ring, a metathesis reaction is described as a minor side process to give mono fluorinated alkenes. Overall, this last reaction corresponds to a photo-Wittig reaction and yield amid isosteres. In order to explain the uncommon regioselectivity of the Paternò-Büchi reaction with these alkenes, electrostatic-potential derived charges (ESP) have been determined. In a second computational study, the relative stabilities of the typical 1,4-diradical intermediates of the Paternò-Büchi reaction have been determined. The results well explain the regioselectivity. Further transformations of the oxetanes or previous functionalization of the fluoroalkenes open perspectives for oxetanes as core structures for biologically active compounds.     

Low temperature DSC characterisation of water in opal

A low temperature (?60 to +105 °C) DSC characterisation of opal was carried out to determine the proportion of crystallisable water and to estimate the cavity size in which the crystallisable water is contained. Circa 10 % of the molecular water contained in the opals was found to be crystallisable suggesting that the remaining molecular water is present either trapped in silica cages or surface-adsorbed in micropores. For the opals derived from a sedimentary environment in Australia, the crystallisable water was found to melt in a manner consistent with the melting of bulk water, suggesting that the water is contained in cavities in the opal. The lack of depressed melting temperatures suggested little or no mesoporosity. A volcanic opal specimen of Mexican origin was found to contain both mesoporous and cavity water, while a Tintenbar opal, also of volcanic origin, was found to contain only mesoporous water due to the melting of the crystallisable water, with an estimated pore diameter size range 4–7 nm. The differences in mesoporosity observed between the volcanic and sedimentary opals are consistent with the demarcation in the physical properties observed between these types of opals in previous studies.     

New trends in the chemistry of α-fluorinated ethers, thioethers, amines and phosphines

Fluorine, the most electronegative element plays nowadays a key role in pharmaceutical, agrochemical and material sciences. About 20% of all pharmaceuticals and about 30% of agrochemicals under development or recently introduced on the market contain fluorine. However, when one examines the relevant structures more closely, one quickly recognizes a structural monotony. The same fluorine bearing aromatic or heterocyclic “cores” appear over and over again. The search for novel molecules having “emergent” fluorinated groups and the development of an efficient access toward them is a challenging task for industrial as well as academic laboratories. For example, the trifluoromethoxy group finds increased utility as a substituent in bioactives, but it is still perhaps the least well understood fluorine substituent in currency. The present review will give an updated overview on the synthesis of α-fluorinated ethers, thioethers, amines and phosphines.