Search results for "stereo"

Enhanced Activity and Stereoselectivity of Polystyrene-Supported Proline-Based Organic Catalysts for Direct Asymmetric Aldol Reaction in Water

2009

Several polystyrene-supported proline dipeptides and a prolinamide derivative were prepared by thiol–ene coupling. These materials were used as catalysts for the direct asymmetric aldol reaction in water, and results compared with unsupported catalysts in water. Such an approach gave more active or stereoselective catalysts compared to the unsupported compounds, showing that our immobilization procedure may be useful to develop catalytic materials with enhanced performance. Moreover, these catalysts can be recovered and reused for at least nine times without loss of activity or can be easily regenerated when their activity has decreased. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, …

NMR spectroscopy in environmental chemistry:1H and13C NMR parameters of tricyclic polychlorinated C10 hydrocarbons and their oxy derivatives based on…

1999

Two-dimensional homo- and heteronuclear NMR chemical shift correlation techniques were applied in the characterization of five tricyclic polychlorinated C10 hydrocarbons, chlordene (1), heptachlor (2), trans-nonachlor (3), α-chlordene (4) and γ-chlordene (5), which are spread globally in the environment owing to their use as insecticides. Approximate and partly contradictory 1H and 13C NMR chemical shifts reported in the literature were corrected in this work. The chemical shift assignments of 1–5 were based on DQF COSY, HMQC and HMBC experiments. In addition, an INADEQUATE experiment was needed to ascertain the 13C chemical shifts assignment of 2. The nJ(H,H)s of 1–5 were solved by compute…

Phenylethynyl- and Phenylethenylmetacyclophanes with π,π Interactions

1999

Alternating Ferro- and Antiferromagnetic Interactions in a Chainlike CuII Coordination Polymer

1993

Die selektive invers-voltammetrische Bestimmung des Antimons in salzsauren Lösungen nach Lösungswechsel in einer einfachen Durchflußzelle

1987

The selective invers-voltammetric determination of antimony in a simple flow-through cell in hydrochloric acid solutions is described. After double medium exchange for post-electrolysis and inverse-voltammetric determination, the determination of antimony is possible in the presence of a large excess of copper, bismuth and other elements. The limit of determination is 0.2–0.3 ppb Sb, the reproducibility 1.5% (10 ppb Sb).

A Tale of Two Isomers: Enhanced Antiaromaticity/Diradical Character versus Deleterious Ring‐Opening of Benzofuran‐fused s ‐Indacenes and Dicyclopenta…

2021

We examine the effects of fusing two benzofurans to s-indacene (indacenodibenzofurans, IDBFs) and dicyclopenta[b,g]naphthalene (indenoindenodibenzofurans, IIDBFs) to control the strong antiaromaticity and diradical character of these core units. Synthesis via 3-functionalized benzofuran yields syn-IDBF and syn-IIDBF. syn-IDBF possesses a high degree of paratropicity, exceeding that of the parent hydrocarbon, which in turn results in strong diradical character for syn-IIDBF. In the case of the anti-isomers, synthesized via 2-substituted benzofurans, these effects are decreased; however, both derivatives undergo an unexpected ring-opening reaction during the final dearomatization step. All th…

ChemInform Abstract: Tetraarylmethane Analogues in Group 14. Part 2. Ph4-nSi(p-Tol)n and Ph4-nSn(p-Tol)n (n = 0-4): Effect of the p-Tolyl Substituent…

2010

The Measurement of the CO2 Hb Binding Curve of Human Hemoglobin by 13C-NMR Spectrometry

1980

It is well known that under physiological conditions CO2 binds to the four terminal amino groups of hemoglobin (Hb) (Kilmartin and Rossi-Bernardi, 1971). The carbamino compounds which are formed by this reaction are involved in the Haldane effect.

Yttrium Hydrido Complexes that Contain a Less “Constrained Geometry” Ligand:  Synthesis, Structure, and Efficient Hydrosilylation Catalysis

2001

σ-Bond metathesis of the new linked amino-cyclopentadiene (C5Me4H)CH2SiMe2NHCMe3 with Y(CH2SiMe3)3(THF)2 gave the alkyl-yttrium complex [Y(η5:η1-C5Me4CH2SiMe2NCMe3)(CH2SiMe3)(THF)] (1) in 66% yield. Compound 1 was characterized by NMR spectroscopy and X-ray crystal structure analysis. By hydrogenolysis, 1 was quantitatively converted into the dimeric hydride [Y(η5:η1-C5Me4CH2SiMe2NCMe3)(THF)(μ-H)]2 (2). X-ray crystal structure analysis revealed a Y2H2 core connected to two [Y(η5:η1-C5Me4CH2SiMe2NCMe3)(THF)] fragments in a skewed manner, with a relatively long yttrium−yttrium distance of 3.7085(8) A. In solution, two diastereomers were observed by 1H NMR spectroscopy at −78 °C. Dimer 2 was s…

Synthesis, characterization and X-ray crystal structures of cyclam derivatives. 7. Hydrogen-bond induced allosteric effects and protonation cooperati…

2005

The unprecedented cooperative protonation properties displayed by a barrel-shaped macrotricyclic tetraamine incorporating two 14-membered bisamide rings maintained in a face-to-face arrangement is rationalized in terms of allosteric effects upon binding of the first and third protons.