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81.
Formation of 4-, 5- and 6-membered heterocycles by ambidoselective cyclization of enolate anions N-Acylmethyl-N-chloracetyl-2,6-dimethylanilines 4 were cyclized with base to 4-, 5- or 6-membered ring compounds, depending on the substituent R2 (Scheme 2). All products can be rationalized as derived from the intermediate enolate anions a and b . The enolate anion a reacts by intramolecular alkylation to yield either 1, 4-oxazines 5 or azetidines 6 (Schemes 1, 3 and 7). The regioselectivity observed is expected on the basis of the allopolarization principle. The enolate anion b reacts only with formation of a new C? C bond (Scheme 5). Comparison with the behaviour of the 2, 6-unsubstituted anilines 9, 1a and 12 , shows a strong dependence not only on electronic but also on steric factors (Scheme 4 and 6). 相似文献
82.
Štefan Toma Anton Gáplovský Milan Hudeček Zuzanna Langfelderová 《Monatshefte für Chemie / Chemical Monthly》1985,116(3):357-364
The electronic absorption spectra of 22 arylferrocenes and their arylferricenium salts with pentacyanopropenide (PCNP) were recorded. The attemptedHammett correlation of max of the d-d transition bands of arylferrocenes revealed that this band is substituent dependent only for strong electron-withdrawing substituents. Excellent correlation of max of the d-d transition bands with + constants was found in the case of arylferricenium cations. Good correlations of max was also found with theE
1/2 oxidation potentials measured by cyclic voltametry.
Substituentenabhängigkeit des d-d-Überganges in den Elektronenabsorptions-Spektren von Arylferrocenen und entsprechenden Arylferricenium-Salzen
Zusammenfassung Elektronenabsorptions-Spektren von 22 Arylferrocenen und ihren Arylferricenium-Pentacyanopropenid-Salzen wurden gemessen. VersuchteHammett-Korrelationen des längstwelligen d-d-Überganges (max) zeigten, daß diese Bande nur von stark elektronenanziehende Substituenten abhängig ist. Im Fall der Arylferricenium-Kationen wurde eine ausgezeichnete Korrelation zwischen max der d-d-Bande und den +-Konstanten festgestellt. Eine gute Korrelation der max-Werte wurde auch mit denE 1/2 Oxidationspotentialen gefunden, die durch cyclische Voltametrie meßbar sind.相似文献
83.
Milan Kunz 《Journal of mathematical chemistry》1993,13(1):145-151
Differences between topological and geometrical distance matrices are examined. Some examples of geometrical distances when graphs are embedded in spaces of different dimensions are given. Relations of topological distance matrices to other graph matrices are shown. The topological distance matrices are defined in the Hilbert space and their elements are distances through the graph lattices. 相似文献
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The response of a single TE102 and double TE104 rectangular cavity to the insertion of samples contained in tubes with variable wall thickness and a quartz Dewar into the cavity has been analyzed. A direct, indirect, and concurrent (positive or negative) “lens effect” inside the double TE104 rectangular cavity is discussed. The experimental dependence of the EPR signal intensity on the wall thickness of the sample tube, δ, for the line-like samples with identical length of the sample material column, L=30 mm, recorded in the microwave cavity showed a directly proportional increase of the relative “lens effect” with the increase of the wall thickness of the tube in the interval, δ∈<0.1 mm, >0.5 mm. The insertion of the variable-temperature double-wall quartz Dewar (home-built, resonant frequency shift, ca. −300 MHz) into the single TE102 rectangular cavity showed the same relative “lens effect”, with ca. 1.5-time increase of the EPR signal intensity, for a point-like sample and the line-like samples with material columns of diameter of 1 and 1.3 mm, and wall thickness of the sample tubes, δ∈<0.1 mm, >0.5 mm. The increased effect of the Dewar arises because the active volume of the quartz Dewar tube walls is always much more larger than the active volume of the sample tube wall. In the case of the double TE104 rectangular cavity, the insertion of the quartz Dewar: (i) into the same cavity, in which the sample is present, caused a direct “lens effect”, with ca. 1.8-fold increase of the EPR signal intensity; however, (ii) into the complementary cavity, in which the sample is absent, caused an indirect “lens effect”, with ca. 0.6-fold decrease of the EPR signal intensity. With the Dewar and sample in one cavity and a large empty sample tube in the complementary cavity, a concurrent (positive or negative) “lens effect” can be observed. Thus, the possible increase/decrease of the EPR signal intensity depends on the volume ratio of the quartz Dewar tube walls and large sample tube wall inserted into the double TE104 rectangular cavity. Each of the above phenomena may be a significant source error in quantitative EPR spectrometry unless the samples to be compared in the quantitative EPR analysis are contained in sample tubes having the same wall thickness and each EPR spectra should be recorded inside an identical quartz Dewar. 相似文献
86.
We show that the two-dimensional isotropic ferromagnetic rotator model exhibits a first order phase transition if the interaction decays asr
– with 2<<4.Work supported by Fonds National Suisse de la Recherche Scientifique. 相似文献
87.
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Vít Kremláček Erik Kertész Prof. Zoltán Benkő Milan Erben Robert Jirásko Prof. Aleš Růžička Prof. Roman Jambor Prof. Libor Dostál 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(52):13096-13097
Invited for the cover of this issue are Zoltán Benkő, Libor Dostál and co-workers at the University of Pardubice and the Budapest University of Technology and Economics. The image depicts signs for the two different pathways representing the two differing reaction types which were clearly observed for 2,1-benzazaphosphole. Read the full text of the article at 10.1002/chem.202101686 . 相似文献