Solvent-dependent oxidative coupling of 1-aryl-1,3-dicarbonyls and styrene

This report describes the scope and mechanism of the solvent-dependent, chemoselective oxidative coupling of 1-aryl-1,3-dicarbonyls with styrene using Ce(IV) reagents. Dihydrofuran derivatives are obtained when reactions are performed in methanol whereas α-tetralones can be selectively synthesized in acetonitrile and methylene chloride. Mechanistic studies are consistent with the rate of solvent-assisted deprotonation of a radical cation intermediate playing an integral role in the selective formation of products.     

Physically nonlinear and related approximate theories of elasticity,and their invariance properties

The existing developments of physically nonlinear elasticity have several shortcomings. With the aim of remedying these deficiencies, a number of approximate theories of elasticity are discussed in the present paper and, in particular, a theory of physically nonlinear elasticity is systematically developed. More specifically, stress-strain relations for anisotropic physically nonlinear materials are derived. The method of Casey & Naghdi [1] is then applied to obtain properly invariant results. This method involves the use of auxiliary motions obtained by removing from any given motion the translation and rotation at any one particle, called a pivot. The auxiliary motions represent the original motions in the approximate theory. The connection between the transformation of fields under a change of pivot and invariance requirements associated with the auxiliary motions is investigated.     

Synthesis, structure, and properties of a T-shaped 14-electron stiboranyl-gold complex

A cyclic stiboranyl-gold complex (1) supported by two 1,8-naphthalenediyl linkers has been synthesized and structurally characterized. The gold atom of this complex adopts a T-shaped geometry and is separated from the antimony center by only 2.76 ?. Surprisingly, the trivalent gold atom of this complex is involved in an aurophilic interaction, a phenomenon typically only observed for monovalent gold complexes. This phenomenon indicates that the stiboranyl ligand possesses strong σ-donating properties making the trivalent gold atom of 1 electron rich. This view is supported by DFT calculations as well as Au L(3)- and Sb K-edge XANES spectra which reveal that 1 may also be described as an aurate-stibonium derivative. In agreement with this view, complex 1 shows no reactivity toward the halides Cl(-), Br(-), and I(-). It does, however, rapidly react with F(-) to form an unprecedented anionic aurate fluorostiborane complex ([2](-)) which has been isolated as the tetra-n-butylammonium salt. The increased coordination number of the antimony center in this anionic complex ([2](-)) does not notably affect the Au-Sb separation (2.77 ?) or the geometry at the gold atom which remains T-shaped.     

Synthesis and characterization of poly(2‐ethylhexyl methacrylate) copolymers containing pendant,self‐complementary multiple‐hydrogen‐bonding sites

The synthesis and characterization of copolymers containing 2‐ethylhexyl methacrylate and a quadruple‐hydrogen‐bonding site, 2‐ureido‐4[1H]‐pyrimidone methacrylate (UPyMA), are described. An analogous dimeric hydrogen‐bond‐containing copolymer based on 2‐ethylhexyl methacrylate and methacrylic acid (PEHMA‐co‐MAA) was also synthesized for comparative purposes. The glass‐transition temperatures of the poly(2‐ethylhexyl methacrylate‐co‐2‐ureido‐4[1H]‐pyrimidone methacrylate) (PEHMA‐co‐UPyMA) series increased linearly with increasing UPyMA content. Creep compliance measurements as a function of temperature indicated a decrease in the creep compliance with increasing UPyMA content over the range of 1–10 mol % UPyMA. Melt rheological analysis also showed an increase and lengthening of the plateau modulus as a function of frequency with increasing UPyMA content, as well as increasing complex viscosity as a function of temperature. The analogous PEHMA‐co‐MAA copolymer, which contained 11 mol % methacrylic acid, showed, in the melt rheological analysis, behavior similar to that of the PEHMA‐co‐UPyMA copolymer containing only 1 mol % UPyMA units. The multiple‐hydrogen‐bond‐containing copolymers were successfully analyzed with time–temperature superposition for the construction of master curves. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 4618–4631, 2005     

Large Molecules as Models for Small Particles in Aqueous Geochemistry Research

Many questions that geochemists now pose about mineral surfaces concern the properties of individual molecular functional groups. These questions can be answered directly with large aqueous molecules where the positions of atoms can be determined with accuracy and related to the reactive properties. It is time to abandon this approach with colloidal solid suspensions and employ aqueous molecular clusters. The reactive properties of individual oxygens can be determined separately using these aqueous clusters in spectroscopic studies. These molecules are sufficiently large (1–5 nm) that they overlap in size with the smallest colloids, yet the bond lengths and atom positions can be determined unequivocally from X-ray structural studies. In this paper we present research on a 2-nm cluster that provides a particular useful example. These molecules, unlike surface structures that are inferred from bulk structures, allow direct comparison of experimental data with molecular simulations.