Search results for "Optically active"
showing 10 items of 31 documents
Bleaching and thermal recovery of PL emissions in natural silica
2000
Abstract We have investigated the bleaching of two photoluminescence (PL) emissions at 3.1 and 4.2 eV and the related growth of an electron spin resonance (ESR) signal, consisting in a hyperfine doublet split by 11.8 mT, in natural silica γ-irradiated by low doses, up to 1 Mrad. These observations definitely support the existence of a conversion mechanism, from optically active defects to paramagnetic ones. To further investigate this conversion process and the stability of the γ-induced paramagnetic centers, we performed PL and ESR measurements in samples that, after a γ exposure at 1 Mrad dose, were thermally treated at various temperatures ranging from 330 to 430 K. We found that the int…
Optically active titanium complexes containing a tridentate linked amido-cyclopentadienyl ligand
2000
Optically active titanium complexes Ti{η5:η1-C5R4SiMe2NC6H10 (OCH2Ph)-2}Cl2 (R = H, Me), containing a cyclopentadienyl ligand linked to the chiral trans-2-benzyloxycyclohexylamido group, were synthesized and characterized in both enantiomerically pure forms. A single crystal X-ray structure analysis of (−)-(R,R)-Ti{η5:η1-C5H4SiMe2NC6H10(OCH2Ph)-2}Cl2 shows a structure in which the benzyloxy group in the amido sidechain is not interacting with the titanium center. Upon activation with n-butyllithium, these complexes hydrogenate acetophenone N-benzylimine with low enantioselectivity. Chirality 12:472–475, 2000. © 2000 Wiley-Liss, Inc.
ChemInform Abstract: Flexible Synthesis of Planar Chiral Azoninones and Optically Active Indolizidinones.
2015
Synthesis and characterization of optically active 2,4-disubstituted-2-oxazolines and their polymerization
1994
Four different optically active 2,4-disubstituted-2-oxazolines were synthesized and characterized. Cationic polymerization of these oxazolines were studied. Three of the oxazolines could be polymerized using methyl trifluoromethanesulfonate as initiator. S-(–)-2-Phenyl-4-isopropyl-2-oxazoline could not be polymerized under the conditions used.
Zur Stereochemie der Oxidation chiraler, tertiärer Phosphine mit Dimethylsulfoxid
1976
Es wird uber den sterischen Verlauf der Oxidation der optisch aktiven, tertiaren Phosphine 3 and 4 mit Dimethylsulfoxid berichtet. Diese Umsetzung verlauft nur in Gegenwart elektrophiler Katalysatoren (Tabelle 1). Je nach Art and Menge des Katalysators zeigt die Stereochemie der Reaktion entweder uberwiegende Inversion oder Retention der Konfiguration am Phosphor an (Tabellen 2, 3); in einigen Fallen wird jedoch fast vollstandige Racemisierung beobachtet (Tabelle3). Auf der Grundlage dieser stereochemischen Resultate werden mogliche Mechanismen fur diese Umsetzung diskutiert. The Sterochemistry of the Oxidation of Chiral Tertiary Phosphines by Means of Dimethyl Sulfoxide The steric course o…
The reaction of optically active α-aminocarboxylic acid hydrazides with triethyl orthoesters
2011
New derivatives of 2-(1-amino-1-phenylmethyl)-1,3,4-oxadiazole and 1,2,4-triazin-6-one were synthesised in the reactions of optically active α-aminocarboxylic acid hydrazides and triethyl orthoesters in xylene. The electronic and steric effects of substituents at the α position influencing the formation of five- or six-membered products are discussed.
Studium zum Vorgang der Wasserstoffübertragung, 50. Elektroreduktion und phasentransferkatalysierte Borhydrid-reduktion prochiraler Ketone
1978
Prochirale Carbonylverbindungen wurden in die entsprechenden sekundaren Alkohole ubergefuhrt a) durch Elektroreduktion und b) mit NaBH4, in beiden Fallen mit den gleichen Ephedriniumsalzen, und zwar fur a) als optisch aktive Leitsalze und fur b) als optisch aktive Phasentransfer-Katalysatoren. Es wurden bei der Elektroreduktion und bei der Phasentransfer-Katalyse die Ausbeuten an Carbinol (und Pinakol)3), die optische Ausbeute und die absolute Konfiguration des bevorzugt gebildeten Enantiomeren bestimmt. In der uberwiegenden Mehrzahl der untersuchten Beispiele besitzen die unter Mitwirkung optisch aktiver Ephedriniumsalze nach beiden Methoden erhaltenen Uberschusenantiomeren die entgegenges…
A New Algorithm for the Retrieval of Sun Induced Chlorophyll Fluorescence of Water Bodies Exploiting the Detailed Spectral Shape of Water-Leaving Rad…
2021
Sun induced chlorophyll fluorescence (SICF) emitted by phytoplankton provides considerable insights into the vital role of the carbon productivity of the earth’s aquatic ecosystems. However, the SICF signal leaving a water body is highly affected by the high spectral variability of its optically active constituents. To disentangle the SICF emission from the water-leaving radiance, a new high spectral resolution retrieval algorithm is presented, which significantly improves the fluorescence line height (FLH) method commonly used so far. The proposed algorithm retrieves the reflectance without SICF contribution by the extrapolation of the reflectance from the adjacent regions. Then, the SICF …
Copper-catalysed enantioselective Michael addition of malonic esters to β-trifluoromethyl-α,β-unsaturated imines
2017
[EN] Copper triflate-BOX complexes catalyse the enantioselective conjugate addition of methyl malonate to beta-trifluoromethyl-alpha,beta-unsaturated imines to give the corresponding enamines bearing a trifluoromethylated stereogenic centre with good yields, and diastereo- and enantioselectivities. The usefulness of the method has been shown with the synthesis of optically active beta-trifluoromethyl delta-amino esters and optically active trifluoromethyl piperidones.
Two new metabolites from the endophytic fungus Xylaria sp. isolated from the medicinal plant Curcuma xanthorrhiza
2015
Abstract The endophytic fungus Xylaria sp. was isolated from healthy leaves of Curcuma xanthorrhiza, collected on the island of Timor, Indonesia. Two new compounds (1 and 2), together with the known resacetophenone (3), were isolated and their structures were elucidated on the basis of comprehensive NMR and mass spectral analyses. The enantiomers of rac-1 were separated by chiral HPLC and their HPLC-ECD spectra were recorded to determine the absolute configuration on the basis of TDDFT-ECD calculations. The (3R,3aR, 9aR) absolute configuration of the optically active 2 was established by comparing the experimental solution ECD spectrum with the TDDFT ones computed for the gas phase and solu…