Comparison of Conventional and Microwave Assisted Reactions Giving Aromatic Oxazolidines

Summary. By reaction of aromatic aldehydes with (-)-ephedrine aromatic 1,3-oxazolidines can be obtained. The reaction was carried out either at conventional conditions or by microwave heating. The different diastereomeric ratios were determined by means of ¹H NMR spectroscopy.Received December 19, 2002; accepted December 23, 2002 Published online June 2, 2003     

On mappings preserving orthogonality of non-singular vectors

Letq be a regular quadratic form on a vector space (V,F) and letf be the bilinear form associated withq. Then, \(\dot V: = \{ z \in V|q(z) \ne 0\} \) is the set of non-singular vectors ofV, and forx, y ∈ \(\dot V\) , ?(x, y) ?f(x, y) ²/(q(x) · q(y)) is theq-measure of (x, y), where ?(x,y)=0 means thatx, y are orthogonal. For an arbitrary mapping \(\sigma :\dot V \to \dot V\) we consider the functional equations $$\begin{gathered} (I)\sphericalangle (x,y) = 0 \Leftrightarrow \sphericalangle (x^\sigma ,y^\sigma ) = 0\forall x,y \in \dot V, \hfill \\ (II)\sphericalangle (x,y) = \sphericalangle (x^\sigma ,y^\sigma )\forall x,y \in \dot V, \hfill \\ (III)f(x,y)^2 = f(x^\sigma ,y^\sigma )^2 \forall x,y \in \dot V, \hfill \\ \end{gathered} $$ and we state conditions on (V,F,q) such thatσ is induced by a mapping of a well-known type. In case of dimV ∈N?{0, 1, 2} ∧ ∣F∣ > 3, each of the assumptions (I), (II), (III) implies that there exist aρ-linear injectionξ :V →V and a fixed λ ∈F?{0} such thatF x ^σ =F x ^ξ ?x ∈ \(\dot V\) andf(x ^ξ,y ^ξ)=λ · (f(x, y))^ρ ?x, y ∈V. Moreover, (II) implies ρ =id _F ∧q(x ^ξ) = λ ·q(x) ?x ∈ \(\dot V\) , and (III) implies ρ=id _F ∧ λ ∈ {1,?1} ∧x ^σ ∈ {x ^ξ, ?x ^ξ} ?x ∈ \(\dot V\) . Other results obtained in this paper include the cases dimV = 2 resp. dimV ?N resp. ∣F∣ = 3.     

On non-semisplit extensions,tensor products and exactness of groupC *-algebras

Summary We show the existence of a block diagonal extensionB of the suspensionS(A) of the reduced groupC ^*-algebraA = C _r ^* (SL ₂()), such that there is only oneC ^*-norm on the algebraic tensor productB ^op B, butB is not nuclear (even not exact). Thus the class of exactC ^*-algebras is not closed under extensions.The existence comes from a new established tensorial duality between the weak expectation property (WEP) of Lance and the local variant (LLP) of the lifting property.We characterize the local lifting property of separable unitalC ^*-algebrasA as follows:A has the local lifting property if and only if Ext (S(A)) is a group, whereS(A) is the suspension ofA.If moreoverA is the quotient algebra of aC ^*-algebra withWEP (for brevity:A isQWEP) but does not satisfyLLP then there exists a quasidiagonal extensionB of the suspensionS(A) by the compact operators such that on the algebraic tensor productB ^op B there is only oneC ^*-norm.The question if everyC ^*-algebra isQWEP remains open, but we obtain the following results onQWEP: AC ^*-algebraC isQWEP if and only ifC ^** isQWEP. A von NeumannII ₁-factorN with separable predualN _* isQWEP if and only ifN is a von Neumann subfactor of the ultrapower of the hyperfiniteII ₁-factor. IfG is a maximally almost periodic discrete non-amenable group with Haagerup's Herz-Schur multiplier constant _G =1 then the universal groupC ^*-algebraC ^*(G) is not exact but the reduced groupC ^*-albegraC _r ^* (G) is exact and isQWEP but does not satisfyWEP andLLP.We study functiorial properties of the classes ofC ^*-algebras satisfyingWEP, LLP resp. beingQWEP.As applications we obtain some unexpected relations between some open questions onC ^*-algebras.Oblatum 13-IV-92Work partially supported by DFG     

Correlations of substituent parameters with the carbonyl stretching force constant in arenetricarbonylchromium complexes

Correlations are established between selected substituent parameters (σ_I,σ_P, σ_R^P,σ_P^O,σ_R^O) and the carbonyl stretching force constant, k(CO), for 28 mono and poly-substituted tricarbonylchromium-complexed arene compounds. On the basis of the statistical results it is concluded that the overall electronic substituent effect transmitted to the carbonyl groups involves both mesomeric and inductive mechanisms. Within the restricted domain, including substituent group and benzene ring, transmission proceeds largely by resonance, with a minor inductive (through-bond and field) effect operative in the same domain. Further transmission from the substituted arene ring to the chromium atom predominantly involves an inductive mechanism. This result, in support of existing literature data, suggests appreciable participation of the ring carbon σ framework in the metal—ring bond formation.     

Differential determination of chromium(VI) and total chromium in natural waters using flow injection on-line separation and preconcentration electrothermal atomic absorption spectrometry.

A rapid, sensitive and selective method for the differential determination of CrIII and CrVI in natural waters is described. Chromium(vi) can be determined directly by flow injection on-line sorbent extraction preconcentration coupled with electrothermal atomic absorption spectrometry using sodium diethyldithiocarbamate as the complexing agent and C18 bonded silica reversed-phase sorbent as the column material. Total Cr can be determined after oxidation of CrIII to CrVI by potassium peroxydisulfate. Chromium(III) can be calculated by difference. The optimum conditions for sorbent extraction of CrVI and oxidation of CrIII to CrVI are evaluated. A 12-fold enhancement in sensitivity compared with direct introduction of 40 microliters samples was achieved after preconcentration for 60 s, giving detection limits of 16 ng l-1 for CrVI and 18 ng l-1 for total Cr (based on 3 sigma). Results obtained for sea-water and river water reference materials were all within the certified range for total Cr with a precision of better than 10% relative standard deviation in the range 100-200 ng l-1. The selectivity of the determination of CrVI was evaluated by analysing spiked reference materials in the presence of CrIII, resulting in quantitative recovery of CrVI.     

Synthesis and spectroscopic features of bis(tetramethylammonium) and bis(benzyltriethylammonium) salts possessing a μ-oxo-bis(trichloroferrate) anion structure

Summary The two -oxo-bis(trichloroferrate) salts (1) and (3) with diamagnetic ammonium cations are prepared as prototype compounds possessing an oxo-bridged dimer anion structure in which each iron(III) centre coordinates tetrahedrally to the three Cl ligands in addition to the bridging ligand. Antiferromagnetic coupling between the two iron centres in the anion complex is indicated by the low room-temperature effective magnetic moments (1.71–1.74 _B). The i.r. and electronic absorption spectra are in accord with the proposed anionic oxygen bridge structure.     

Morphologie de Réseaux Polymères Interpénétrés préparés en deux étapes

Résumé Un nouveau modèle thermodynamique prédisant la taille des domaines des réseaux polymères interpénétrés préparés en deux étapes est décrite. Les paramètres influents sont la tension interfaciale et la densité de réticulation des deux polymères, ainsi que la composition. A l'aide de la microscopie électronique à balayage, la théorie a été vérifiée pour le système poly(acrylate den-butyle)/polystyrène.

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A series of sequential interpenetrating polymer networks, IPN's, of poly(n-butyl acrylate) and polystyrene were prepared. A new equation predicting the domain size in IPN's is summarized and shown to yield agreement with the morphologies observed via scanning electron microscopy. The experimental variables required to determine the domain size include the volume fraction and crosslink level of each polymer, the interfacial tension and the temperature.

     

Organotin Dyes: Synthesis and Structural Characterization of Dibutyltin and Dimethyltin Complexes with 2, 2′‐Dihydroxyazobenzene

The preparation and structures of 2, 2′‐dihydroxyazobenzenato‐dibutyl‐tin [Bu₂SnL] and 2, 2′‐dihydroxyazobenzenato‐dimethyl‐tin [Me₂SnL] are described. The complexes were characterized by IR, NMR (¹H, ¹³C, ¹¹⁹Sn) and UV/VIS spectra. The crystal structures were determined by X‐ray diffraction on single crystals. [Bu₂SnL]: monoclinic, space group P2₁/c, cell constants at 208 K: a = 860.73(5), b = 973, 51(18), c = 2340.0(3) pm, β = 93.615(11)°; R₁ = 0.0546. [Me₂SnL]: orthorhombic, space group Pbcn, cell constants at 208 K: a = 1914.6(4), b = 1041.3(3), c = 1323.27(14) pm; R₁ = 0.0529.     

Novel unsymmetrical PCP′ pincer ligands and their palladium(II) complexes

Synthetic routes towards novel PCP′ pincer ligands were devised. Ligand 1-(Pr₂ⁱPOCH₂)-3-(Bu₂^tPCH₂)(C₆H₄) is prepared in a three step synthesis from 1,3-benzenedimethanol and 1-(Pr₂ⁱPO)-3-(Bu₂^tPCH₂)(C₆H₄) is accessible in three steps from 3-hydroxybenzylalcohol. Both their palladium(II) complexes are prepared in good yields but are distinctly different since [PdCl{(C₆H₃)(OPPr₂ⁱ)-2-(CH₂PBu₂^t)-6}] possesses two five-membered palladacycles, whereas [PdCl{(C₆H₃)(CH₂PBu₂^t)-2-(CH₂OPPr₂ⁱ)-6}] is unusual for a pincer complex in that it contains both five- and six-membered palladacycles. Both compounds also represent the first examples of pincer complexes where one donor is a phosphinite and the other is a phosphine. The X-ray structures of these complexes were solved and are discussed. The data reveal that an increase in the metallacycle ring-size leads to changes in bond lengths, but more importantly to significant increases in the bond angles.     

Characterizing moore groups by tensor products of irreducible representations

It is shown that all irreducible representations of a σ-compact Lie group G have to be finite dimensional provided that for every π in the reduced dual of G the tensor product π ? \(\bar \pi \) has a discrete support.