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931.
Helmut Dorn 《Tetrahedron letters》1985,26(42):5123-5126
Highly polar 1,3-dipoles like pyrazolid-3-one azomethinimines stereospecifically add polar dipolarophiles . A suggested “non cisoid” adduct of E-β-nitrostyrene is generated by epimerization at C-2 , catalysed by Kieselgel 40 MERCK and small amounts of pyrazolid-3-one. 相似文献
932.
933.
934.
Helmut Guth 《Helvetica chimica acta》1996,79(6):1559-1571
The intense sweet and coconut-like smelling odorant 1 , named ‘wine lactone’, was isolated from different wine varieties. The chemical structure of this compound, which has not yet been detected in wine or a food, was identified by high-resolution mass spectrometry (HR-MS) as 3a,4,5,7a-tetrahydro-3,6-dimethylbenzofuran-2(3H)-one. For the evaluation of the configuration of wine lactone, stereochemically controlled syntheses were developed. All eight isomers were characterized by NMR, MS, IR, and CD measurements. The configuration of ‘wine lactone’ was in agreement with synthesized (3S,3aS,7aR)-enantiomer ( 1a ) on the basis of enantioselective GC. For this isomer, the lowest odor threshold (0.02 pg/1 air) was detected. 相似文献
935.
Erik H. Licht Helmut G. Alt Wolfgang Milius Sultan Abu-Orabi 《Journal of organometallic chemistry》1998,560(1-2)
The preparation and characterization of the substituted bis(cyclopentadienyl) zirconium dichloride complexes (η5-C5H4CMe2C9H7)2ZrCl2 (1a, b) is reported. The isomer mixture of 1a, b was treated with different reducing agents such as sodium and n-butyllithium under various reaction conditions. In these reactions CC and CH activation and cleavage reactions were observed. In combination with methylaluminoxane (MAO) 1a, b and 3 showed low activities as homogeneous ethylene polymerization catalysts and no activities towards propylene. Compounds 2 and 3 were characterized by NMR spectroscopy and X-ray crystallography. 相似文献
936.
In contrast to Fe+/diol complexes, gas-phase dehydrogenation of the corresponding FeII alkoxides, [FeO(CH2)nCH2OH]+, is a highly specific process in the course of which oxidation of the terminal OH group takes place. Based on labeling studies, this is the exclusive mechanism for n = 2 and 3 (Scheme: path ); for higher homologues, as for example [FeOf(CH2)7CH2OH]+, the labeling data demonstrate that an additional mechanism is operative, involving the dehydrogenation of internal positions of the alkyl chain (path ). The Fe+-mediated oxidation –CH2OH → –CHO +H2: constitutes one of the rare examples of O-H bond activation by late cationic transition-metal ions. 相似文献
937.
The notion reflection group (,
) was introduced in order to give group theoretical characterizations of absolute planes. Here we consider reflection groups with midpoints and associate to each of them an incidence structure
. Then
is an incidence space which dimension can assume any value. The motion group together with the set
of all reflections in points of a Euclidean or hyperbolic geometry are examples of reflection groups with midpoints. Furthermore the set
can be turned into a K-loop. The precise results are summarized in the theorems at the end of the paper.Cordially dedicated to Sibylla Prieß on the occasion of her 60th birthdaySupported by the NATO Scientific Affairs Division grant CRG 900103. 相似文献
938.
Helmut H. Schaefer Xiao-Dong Zhang 《Proceedings of the American Mathematical Society》1997,125(1):93-99
We prove that a Baire measure (or a regular Borel measure) on a compact Hausdorff space is sequentially order continuous as a linear functional on the Banach space of all continuous functions if and only if it vanishes on meager Baire subsets, a result parallel to a much earlier theorem of Dixmier. We also give some results on the relation between sequentially order continuous measures on compact spaces and countably additive measures on Boolean algebras.
939.
We characterize right loops (L, +) without, respectively with an incidence fibration F from which one can derive a reflection or a point- reflection structure, respectively a reflection or a point- reflection geometry in the sense of [1]. 相似文献
940.
(MDS)- and Laguerre codes are closely related to geometry and can be used in order to construct certain finite incidence structures. Here we present some structure theorems on near rings, introduce the notion of a coding set of a near ring, which enables us to construct (MDS)-codes, and discuss the same problem for Laguerre codes. To find non trivial Laguerre sets in a near ring is much more difficult.Dedicated to Giuseppe Tallini on the occasion of his 60 th birthday 相似文献