Synthesis of potential ambra odorants: 5,5,9-trimethyldecalyl derivatives

The synthesis of racemic stereoisomeric compounds with the 5,5,9-trimethyldecalin skeleton and an oxygen function at C(1), C(2), or C(3) is described

1 Although racemic decalins are described, only the enantiomer related to steroids is drawn. The projection of the decalins was chosen so as to place the angular methyl group above the plane of the molecule and the oxygen function at C(1), C(2) or C(3) on the left side, as represented by formula 1–6 . The relative configuration of the substituents in decalins is designated by using the convention of the steroid series: β, meaning on the same side as the angular methyl group at C(9) and α, meaning on the side opposite from the angular methyl group. The prefix cis or trans refers to the fusion of the decalin ring system, not to the position of the substituents.

. A novel general one-step synthesis of 2-decalones by means of acid catalyzed cyclization of acyclic or monocyclic precursors has been developed.     

Skeletal Rearrangements of Organoalkali Metal Compounds

Organometallic compounds of the alkali metals undergo concerted [1,n] sigmatropic migration of aryl, vinyl, carbonyl, alkoxycarbonyl, silyl, germyl, and related groups. Sigmatropic migration of alkyl, benzyl, and hydrogen occur only under special circumstances and then may occur by an alternate fragmentation-recombination pathway. Allyl groups may migrate by the latter process or by a concerted [2,3] sigmatropic reaction. These molecular rearrangements are discussed from the viewpoint of simple molecular orbital theory. By suitable choice of the alkali metal, temperature, ligands of the alkali cation and/or the solvent, considerable control may be exercised over the rate of rearrangement, the relative migratory aptitude of groups, and the mechanistic pathway.     

Polymerization of vinyl chloride at reduced monomer accessibility. II. Polymerization at subsaturation pressure with emulsion PVC as seed

Vinyl chloride was polymerized at 59–92% of saturation pressure in a water-suspended system at 45–65°C with an emulsion poly(vinyl chloride) (PVC) latex as a seed. A water-soluble initiator was used in various concentrations. The monomer was continuously charged as vapor from a storage vessel kept at lower temperature. Characterization included determination of molecular-weight distribution and degree of long-chain branching by gel permeation chromatography (GPC) and viscometry, thermal dehydrochlorination, and microscopy. The polymerization rate decreases with decreasing pressure but is reasonable even at the lowest pressure. The molecular weight decreases with decreasing pressure and increasing initiator concentration and also with increasing polymerization temperature, if the initiator concentrations are chosen to give a constant initiator radical concentration. The degree of long-chain branching increases with increasing initiator concentration and decreasing monomer pressure but is unaffected by the polymerization temperature, if the initiator radical concentration is kept constant. The thermal stability decreases with decreasing M _n, while the degree of long-chain branching has only a minor influence. The most important factor in the system influencing the molecular parameter is the monomer accessibility.     

Compact abelian groups of automorphisms of simpleC *-algebras

If is a continuous representation of a compact abelian groupG as *-automorphisms of a prime or simpleC ^*-algebraA we study how algebraic properties of the fixed-point algebraA ₀ are reflected in properties of the spectrum of and outerness of ₁,tG. For example, ifA is prime, ()=Sp() if and only ifA ₀ is prime, and the same with simple (instead of prime) whenG is finite. In the latter case the relative commutant ofA ₀ inA is trivial if and only if all ₁l are outer, and ifG is cyclic of prime order all the conditions above are equivalent. This paper replaces the earlier versions [12] and [9].     

On the nonsingle-site character of Bis(2-dimethylsilyl-indenyl)zirconium(IV) dichloride/MAO and Bis(2-trimethylsilyl-indenyl)zirconium(IV) dichloride/MAO: polymerization characteristics and mechanistic implications

Ethene polymerization with bis(2-dimethylsilyl-indenyl)zirconium(IV) dichloride (1)/MAO and bis(2-trimethylsilyl-indenyl)zirconium(IV) dichloride (2)/MAO and ethene-co-1-hexene polymerization with 1/MAO are presented. The end group analysis of homopolymers reveals a pronounced dependence of the termination rate on temperature changes. In combination with the high molecular weights obtained, these results are in accord with theoretical predictions. Gel permeation chromatography, Fourier transform infrared, and 13C NMR analyses of copolymerization products from 1/MAO as a function of comonomer concentration at two different temperature series denote its tendency to form inhomogeneous polymer blends. Thermal analysis and fractionation results of one such blend indicate an inhomogeneity in the enchainment process and the existence of multiple active sites of differing geometry. These indications are further supported by AMBER force field and density functional theory studies of the catalyst precursors and the active site of 1/MAO. For this system, delta-agostic interactions for the stabilization of the zirconium cation are favored over beta-agostic interactions, which, in contrast to the situation in studies on bis-Cp systems, is a sparsely populated species. The gap in activation enthalphies for beta-hydride transfer and elimination is marginalized for these bulky zirconocenes, and conceptually new mechanisms for the isomerization of the vinyl end groups are discussed. Further, unexpected activation of the silicon-hydrogen bond within the ligand framework is observed with an activation enthalpy as low as 14 kcal/mol.     

Interpretation of capillary pressure curves using invasion percolation theory

Invasion percolation was studied on three-dimensional regular lattices of various node numbers. A new model has been developed to obtain the pore-size distribution from capillary pressure measurements. The new model is superior to the conventional percolation model, since it takes into account the physical trapping of the wetting phase. The irreducible wetting phase saturation includes the film of the wall of the pores, the dead-end pore volume, and the main contribution by pores isolated from the outlet of the medium by the nonwetting phase. This has been related to the node number and the sample 3dimensions. Over 100 capillary pressure curves of consolidated media have been collected. Good agreement was obtained between this data set out and our invasion percolation predictions using node numbers of 6–13, as reported by Mishra and Sharma. The pore-throat size distribution function estimated by our new model is broader than from the conventional percolation and the capillary tube models.Nomenclature c constant - D pore throat diameter [m] - D _max maximum pore diameter [m] - f(D) correlation function of pore throat size and pore body size - L a parameter representing the dimension of a sample - n node number - p pressure [N/m²] - S _n the nonwetting phase saturation - x random number ranging from 0 to 1.0 - X ^a X _t ^a /X/ _t - X _e ^a X _t ^a –X _t ⁱ - X ⁱ X _t ⁱ /X _t ^a - X _nw fraction of pore volume occupied by the injected phase - X _t fraction of pores larger thanD - X _t ^a total accessibility of pores larger thanD - X _t ⁱ total isolation of pores larger thanD - contact angle - interfacial tension [N/m] - (D) pore throat size distribution     

Tables of subgroups,site groups and interchange groups of symmetry point groups and the construction of SALCs

A table listing subgroups and supergroups of 43 chemically important symmetry point groups is presented. Other tables give the site groups and the corresponding interchange groups for those point groups which are of finite order. It is shown how the tables may be used to facilitate the structure determination of metal-ligand and related compounds from spectroscopic data and how the construction of symmetry adapted linear combinations. SALCs, may be simplified. The tables also may be used in factor group analysis.     

High-pressure vapor–liquid equilibria of systems containing ethylene glycol,water and methane: Experimental measurements and modeling

This work presents new experimental phase equilibrium measurements of the binary MEG–methane and the ternary MEG–water–methane system at low temperatures and high pressures which are of interest to applications related to natural gas processing. Emphasis is given to MEG and water solubility measurements in the gas phase. The CPA and SRK EoS, the latter using either conventional or EoS/G^E mixing rules are used to predict the solubility of the heavy components in the gas phase. It is concluded that CPA and SRK using the Huron–Vidal mixing rule perform equally satisfactory, while CPA requires fewer interaction parameters.     

Possible effects on the polyethene chain structure of trimethylaluminum coordination to zirconocene catalysts

Ethene was polymerized with the catalytic systems L₂ZrCl₂/MAO/TMA (where L = Cp, Me₅Cp, or Me₄Cp; Cp = η⁵‐cyclopentadienyl; MAO = methylaluminoxane; and TMA = trimethylaluminum) at 60 °C, 2 bar, and Al_TMA/Zr ratios of 0–2700. The polymerization activity was reduced with the addition of TMA for L = Cp but was almost unaffected for the methyl‐substituted catalysts. Increasing the TMA concentration resulted in a lower molecular weight of the polymer, with the largest effect for L = Me₅Cp. A gel permeation chromatography analysis of the polymers revealed a high molecular weight shoulder and a nearly bimodal distribution for L = Me₅Cp at high TMA concentrations. A possible explanation of such a shoulder in terms of long‐chain branching was ruled out by dynamic viscosity measurements. The origin of this effect more likely stemmed from competition between chain transfer to aluminum and β‐hydrogen transfer reactions at two different sites, one TMA‐sensitive and one TMA‐insensitive. Polymerizations at various pressures and temperatures substantiated this assumption. A clue to the underlying mechanism came from investigations of chain transfer to TMA studied with density functional calculations. Complexation of Me₃Al to Zr was much stronger for L = Cp than for L = Me₅Cp. However, the overall chain‐transfer barrier was much higher for L = Cp. These results agreed both with the reduced activity for L = Cp and with the strongly reduced molecular weight for L = Me₅Cp observed with the addition of TMA. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 3566–3577, 2001     

Adsorption equilibria of binary gas mixtures on graphitized carbon black

Adsorption equilibria for binary gas mixtures (methane-carbon dioxide, methane-ethane, and carbon dioxide-ethane) on the graphitized carbon black STH-2 were measured by the open flow method at 293.2 K. The experimental pressure range was (0 to 1.6) MPa. The extended Langmuir (EL) model and the ideal adsorption solution theory (IAST) have been adopted to predict the equilibria of binary gas mixtures. The results indicate that gas mixtures adsorbed on the homogeneous surface of STH-2 exhibit the nonideal behavior, which is mainly induced by adsorbate-adsorbate interactions. The real adsorption solution theory (RAST) has been used to analyze the property of the adsorbed mixtures. The activity coefficients have been correlated with the Wilson equation. The investigation demonstrates that the nonideality of adsorbed phase is completely dissimilar with the bulk liquid phase. The adsorption of the heavier component would benefit the adsorption of the lighter component.