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51.
52.
Given an expansive action α of ?2 by automorphisms of a compact connected metrizable abelian groupX, we show how the entropy of the action may be decomposed into local contributions, 1 $$h(\alpha ) = \sum\limits_{p \leqslant \infty } {h_p^{(a,b)} } (\alpha )$$ in which the summandh p (a,b) (α) represents thep-adic entropy due to arithmetic or geometric hyperbolicity in the direction (a, b). We recognize thep-adic contribution as an integral over thep-adic unit circle, in analogy with the global counterpart. As (a, b) changes, the decomposition (1) changes only when the line through (a, b) passes through one of a finite collection of critical directions, which are explicitly identified. 相似文献
53.
Cellular algebras 总被引:4,自引:0,他引:4
54.
55.
The thermally stable, terminal phosphinidene complexes [CpM(CO)2(eta1-PNiPr2)]AlCl4(Cp= Cp, Cp*; M = Fe) and [Cp*M(CO)3(eta1-PNiPr2)]AlCl4 (M = Cr, Mo, W) react with Ph2C=N=N to form terminal P-coordinated eta1-phosphaazine and eta3-diazaphosphaallene ligands, respectively, whereas [CpFe(CO)2(eta1-PNiPr2)]AlCl4 reacts with Me3SiCHN2 affording a terminal phosphorus bound eta1-phosphaalkene complex. 相似文献
56.
Graham R. Underwood Brajeswar Paul M. Alice Becker 《Journal of heterocyclic chemistry》1976,13(6):1229-1232
Pyridoxol, protected by acetylation of the hydroxyl groups, has been converted to its N-oxide which upon reaction with perfluoroacetie anhydride yields a 2-nor-2-hydroxymethylpyridoxol derivative as an intermediate. This compound undergoes acyl migration from the 3-position. Protection of the pyridoxol hydroxyls by benzylalion followed by the same treatment yields the unrearranged α2-hydroxy derivative. This compound has been converted to a series of α2-substituted pyridoxols (X = -Cl, -Br, -OCOCH3, -OCH3, -OC2H5). 相似文献
57.
James R. Gord Stevan R. Horning Joseph M. Wood R. Graham Cooks Ben S. Freiser 《Journal of the American Society for Mass Spectrometry》1993,4(2):145-151
We report studies of the internal energy deposited during activation of mass-selected ions through electron-ion collisions. Characteristic fragmentations of the molecular ion of limonene and W(CO) n/+ (n = 1–6) indicate that electron-induced dissociation in a Fourier transform ion cyclotron resonance mass spectrometer proceeds via multiple collisions and that the average internal energy deposited during the activation process can be selected to be similar to that associated with electron-impact ionization. Control of the degree of ion excitation through selection of the electron energy, flux, and interaction time with the ions of interest is demonstrated, and advantages of this promising activation technique are discussed. 相似文献
58.
Graham Smith Colin H.L. Kennard Thomas C.W. Mak 《Journal of organometallic chemistry》1985,290(1):c7-c10
The crystal structure of trimethyl(thiomethyl)platmum(IV), [Pt(CH3)3(SCH3)]4, has been determined using X-ray diffraction. The compound has three independent but isostructural tetrameric units in the asymmetric unit. The four metal atoms in each tetramer are linked by bridging thiomethyl sulphurs, with three methyl groups completing the octahedral coordination around each platinum. Mean interatomic distances within the tetramer are PtS, 2.48(2), PtC, 2.00(4), PtPt, 3.80(2) Å, with a mean bridge angle SPtS, 79.1(7)°. 相似文献
59.
In the absence of metal ions, the hydrolysis of 2-methyl-8-acetoxyquinoline and of 5-chloro-8-acetoxyquinoline follow the same reaction paths as those of the parent ester 8-acetoxyquinoline, including an intramolecular catalysis by the quinoline nitrogen. Unlike the hydrolysis of the other esters, that of the 2-methyl compound appears not to be catalysed by metal ions, and this is consistent with the view that catalysis by a metal ion involves the formation of a 7-membered chelate structure. 相似文献
60.
The photoactivated W(CO)(6)/DABCO/THF system has been used for the formal endo-cyclization of alkynes to pyran rings. We found that the regioselectivity of ring closure depends on the relative configuration of the 3,5-dihydroxy-1-alkynes, as well as, more decisively, on the type of O-protective group. Oxygen substitution at the propargylic carbon slows the rate of alkyne insertion and allows for dihydrofuran formation through exo-cyclization. In contrast, the use of bulky silyl ethers or carbon substituents leads to dihydropyrans through endo-cyclization. Substrates bearing leaving groups such as esters, phenols, or thiophenols at the propargylic site eliminate and thus represent a limitation to the cycloisomerization methodology. Propargyl vinyl ethers will rearrange to give dienals instead of glycals. 1,2-Wittig rearrangement products of dihydropyrans are readily prepared and converted to complex bicyclic building blocks for organic synthesis. 相似文献