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141.
The radical yields and rate constants in the quenching reaction of thionine triplet with the complete series of monohalogen substituted anilines as electron donors were determined by flash spectroscopy. Whereas the quenching rate constants show little and unsystematic variation, the radical yields decrease with increasing spin—orbit coupling constant of the halogen substituent. This effect is very sensitive to the position of the halogen in the donor. The results are explained in terms of a heavy atom effect on the intersystem crossing rate constant in a triplet exciplex. 相似文献
142.
Gerhard BringmannStefan Busemann 《Tetrahedron》2003,59(8):1245-1253
The first quantum chemical calculation of the circular dichroism (CD) spectra of michellamines has been achieved, based on a complete quantum chemical conformational analysis. Michellamines are dimeric naphthylisoquinoline alkaloids and thus naturally occurring quateraryls, with a large molecular size and flexibility and equipped with stereogenic centers and axes. 相似文献
143.
Gerhard Bieri Edgar Heilbronner Else Kloster-Jensen Andreas Schmelzer Jakob Wirz 《Helvetica chimica acta》1974,57(5):1265-1283
The photoelectron spectra of 1,5-cyclooctadiyne ( 2 ) and of 1,6-dithiacyclodeca-3,8-diyne ( 3 ) have been recorded. The first four ( 2 ) or six ( 3 ) PE. bands have been assigned as follows; in increasing order of ionization potentials: The relative sequence and the positions of the PE. bands are explained in terms of through-bond and through-space interactions between the basis π-orbitals and σ-orbitals of appropriate symmetry behaviour. An analysis of the PE. spectroscopic data for cyclooctyne ( 1 ) and for ( 2 ) indicates that a cis-bend of the acetylene moiety by θ < 20° leads to a split in energy of the in-plane and out-of-plane basis π-orbitals which is smaller than ∽ 0.2 eV. This is in agreement with the predictions derived from semiempirical models (MINDO/2, SPINDO) and qualitative orbital arguments. However, it is shown by using orbital localization procedures, that the rationales underlying the two semiempirical models differ significantly. 相似文献
144.
Gustav Kortüm und Gerhard Herzog 《Fresenius' Journal of Analytical Chemistry》1962,190(2):239-242
Zusammenfassung Pulvergemische von zwei verschiedenen Modifikationen eines Stoffes oder von zwei Pigmenten lassen sich mit Hilfe diffuser Reflexionsmessungen quantitativ analysieren, wenn die Reflexionsspektren sich in einem zugänglichen Spektralgebiet genügend stark unterscheiden. Die Methode wird am Beispiel der Titandioxyde Rutil und Anatas im einzelnen beschrieben.
Summary Mixtures of two modifications of solid powdered material can be quantitatively analyzed by diffuse reflectance measurements, if the reflectance spectra are sufficiently different in some wavelength range. The method is described with the example of the titanium dioxides rutile and anatase.相似文献
145.
146.
Burghard Grüning Gerhard Holze Albert Gossauer Ludger Ernst 《Helvetica chimica acta》1985,68(6):1771-1781
The transformation of the c-acetic-acid chain of hexamethyl Coα, Coβ-dicyanocobyrinate into an ethyl group (→ 2 ) as well as the synthesis of the pentadecaalkyl-cobalticorrin 6d from commercial cyanocobalamin are described. On reaction of 2 or 6d with O2 in the presence of ascorbic acid, migration of the CH3 group at C(5) to the vicinal position C(6) takes place concomitantly with the introduction of a carbonyl group at C(5). 相似文献
147.
A New Approach to Bicyclo[4.1.0]heptane Derivatives The reaction of the dienone 1 with ethyl α-bromoacetate does not furnish the expected glycidic acid ester 2 but leads to the bicyclo[4.1.0]heptenone derivative 3 . The structure of this new compound has been proved by means of spectroscopic methods (1R, 1H-NMR, 13C-NMR, MS). The elucidation of the configuration at C(7) could be realized by measuring a NOE effect. Other α-alkylated α-bromoacetates react with 1 in the same manner. 相似文献
148.
Gerhard Hamprecht Karl-Heinz Knig Gerd Stubenrauch 《Angewandte Chemie (International ed. in English)》1981,20(2):151-164
Due to their bifunctional character, alkylsulfamoyl chlorides are versatile units for the synthesis of heterocycles, polar sulfamates, and sulfonamides. In the last decade, synthetic methods of general preparative use have been developed, by means of which amine hydrochlorides, isocyanates, aziridines or tertiary alcohols can be reacted with suitable sulfuric acid derivatives to give novel, variously substituted alkylsulfamoyl chlorides. These compounds can subsequently be converted either to previously unobtainable N-alkoxyalkyl-N-alkylsulfamoyl chlorides or to novel heterocycles of the type 1H-2,1,3-benzothiadiazin-4-one-2,2-dioxide, 2H-1,2,6-thiadia-zin-3-one-1,1-dioxide and 2H-1,2,4,6-thiatriazin-5-one-1,1-dioxide; these compounds are examples of interesting models which illustrate the relation between the structure and the action of the compound, and in some cases lead to highly selective, ecologically unobjectionable herbicides. On the other hand, the alkylsulfamoyl chlorides themselves can be N-acylated to give further 3- to 5-atom bifunctional synthesis units, with which novel heterocyclic syntheses can be carried out. Further uses of the alkylsulfamoyl chlorides include the preparation of biologically active sulfamates, and cycloaddition reactions of N-sulfonylamines prepared in situ. 相似文献
149.
Zusammenfassung Die Reaktion zwischen CaSi2 und JCl liefert in einer Festkörperreaktion unter Aufspaltung des Schichtgitters ein stöchiometrisch und strukturell definiertes (SiCl)
n
. Eigenschaften und Hydrolyse der Verbindung werden besprochen. Solvolyse mit Alkoholen führt zu entsprechenden Alkoxyderivaten, die Umsetzung mit Lithiummethyl zur methylierten Verbindung.Mit 2 Abbildungen4. Mitt.:E. Hengge undH. Grupe, Chem. Ber.97, 1783 (1964). 相似文献
150.
Natural products have been synthesized for billions of years in animals, plants, and microorganisms. As a rule they occur enantiomerically pure. Their chiral character corroborates their use in metabolism or as biologically active agents. Natural products may be insufficient in quality or quantity. They have recently begun to become accessible, either unchanged or modified, by biological synthesis; here, too, they are obtained enantiomerically pure. In the last twenty years chemical synthesis has become a major concern of organic chemists. Their target compounds are primarily enantiomerically pure natural products or biologically active variants thereof. 相似文献