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81.
Heinz Günter Viehe Robert Mernyi Lucien Stella Zdenek Janousek 《Angewandte Chemie (International ed. in English)》1979,18(12):917-932
The 100 yers old Wurster's salts have long been recognized as compounds with redical cations. Their unusual stabilization derives partly form capto-dative (cd) substitution. This principle is now discussed as one factor of radical stabilization and it is applied to simple methine derivatives. cd-Substitution has synthetically useful applications: cd-substituents on a carbon atom allow its selective dehydrodimerization. Olefines with geminal and thus cross-conjugated cd-substituents are “radicophilic” and permit twofold carbon radical addition. cd-Substituted olefines are useful antioxidants, polymerization inhibitors and are promising agents in the control of biological radical reactions. Generally, many reactions of cd-substituted molecules appear to involve radicals. 相似文献
82.
《Chemistry (Weinheim an der Bergstrasse, Germany)》2005,11(1):81-93
Efficient electrochemical syntheses of “homocoenzyme B12” ( 2 , Coβ‐(5′‐deoxy‐5′‐adenosyl‐methyl)‐cob(III )alamin) and “bishomocoenzyme B12” ( 3 , Coβ‐[2‐(5′‐deoxy‐5′‐adenosyl)‐ethyl]‐cob(III )alamin) are reported here. These syntheses have provided crystalline samples of 2 and 3 in 94 and 77 % yield, respectively. In addition, in‐depth investigations of the structures of 2 and 3 in solution were carried out and a high‐resolution crystal structure of 2 was obtained. The two homologues of coenzyme B12 ( 2 and 3 ) are suggested to function as covalent structural mimics of the hypothetical enzyme‐bound “activated” (that is, “stretched” or even homolytically cleaved) states of the B12 cofactor. From crude molecular models, the crucial distances from the corrin‐bound cobalt center to the C5′ atom of the (homo)adenosine moieties in 2 and 3 were estimated to be about 3.0 and 4.4 Å, respectively. These values are roughly the same as those found in the two “activated” forms of coenzyme B12 in the crystal structure of glutamate mutase. Indeed, in the crystal structure of 2 , the cobalt center was observed to be at a distance of 2.99 Å from the C5′ atom of the homoadenosine moiety and the latter was found to be present in the unusual syn conformation. In solution, the organometallic moieties of 2 and 3 were shown to be rather flexible and to be considerably more dynamic than the equivalent group in coenzyme B12. The homoadenosine moiety of 2 was indicated to occur in both the syn and the anti conformations. 相似文献
83.
The excess Gibb's free energy of mixing, GE, for ethyl iodide+toluene at 25°C have been obtained from the measured vapor pressuure data. The HE and GE values for ethyl iodide+toluene are positive throughout the ethyl iodide concentration range and GE>HE. The results have been analyzed in terms of Flory and ideal associated model theory of nonelectrolyte solutions. It has been observed that the ideal associated model approach which assumes the presence of AN and A2B molecular species describes well (within±10 J-mol–1 in the worst case) the general dependence of HE on XA (mole fraction of ethyl iodide) over the whole composition range for ethyl iodide+toluene mixtures. The equilibrium constants for A+A AB and 2A+BA2B reactions along with the enthalpies of formation of AB and A2B molecular species have been calculated. 相似文献
84.
K. E. Russell 《Journal of polymer science. Part A, Polymer chemistry》1995,33(3):555-561
Maleic anhydride has been grafted to eicosane and squalane at 60–80°C using 1,2-dichlorobenzene as solvent and benzoyl peroxide as initiator. These hydrocarbons are low molecular weight models for hydrocarbon polymers containing secondary and tertiary hydrogen atoms. In the absence of the hydrocarbon and with monomer concentrations of the order of 1M, low molecular weight poly(maleic anhydride) is formed. On addition of the hydrocarbon, the main product is grafted material and very little homopolymer is formed. The grafts consist primarily of single succinic anhydride units but some of them are short poly(maleic anhydride) chains. Ceiling temperature considerations control the formation of homopolymer in the absence of hydrocarbon substrate. In the presence of eicosane or squalane, initiation of grafting proceeds by hydrogen abstraction from the hydrocarbon. The main factor controlling graft length is then the ratio of the rates of intramolecular hydrogen abstraction and of monomer addition to succinic anhydride radicals © 1995 John Wiley & Sons, Inc. 相似文献
85.
86.
Chibowski E 《Advances in colloid and interface science》2003,103(2):149-172
Nature of contact angle hysteresis is discussed basing on the literature data (Colloids Surf. A 189 (2001) 265) of dynamic advancing and receding contact angles of n-alkanes and n-alcohols on a very smooth surface of 1,1,2,-trichloro-1,2,2,-trifluoroethane (FC-732) film deposited on a silicon plate. The authors considered the liquid absorption and/or retention (swelling) processes responsible for the observed hysteresis. In this paper hysteresis is considered to be due to the liquid film left behind the drop during retreating of its contact line. Using the contact angle hysteresis an approach is suggested for evaluation of the solid surface free energy. Molecular spacing and the film structure are discussed to explain the difference in n-alkanes and n-alcohols behaviour as well as to explain the difference between dispersion free energy gamma(s)(d) and total surface free energy gamma(s)(tot) of FC-732, as determined from the advancing contact angles and the hysteresis, respectively. 相似文献
87.
2-(2-Bromophenyl)ethyl groups have been used as building blocks in radical cyclisation reactions onto azoles to synthesise tri- and tetra-cyclic heterocycles. 2-(2-Bromophenyl)ethyl methanesulfonate was used to alkylate azoles (imidazoles, pyrroles, indoles and pyrazoles) for the synthesis of the radical precursors. Cyclisations of the intermediate aryl radicals yield new 6-membered rings attached to the azoles. The aryl radicals undergo intramolecular homolytic aromatic substitution onto the azole rings. Tributylgermanium hydride has been used with success to replace the toxic and troublesome tributyltin hydride. Initial studies show that the protocol can be used on solid phase resins. The molecular and crystal structures of methyl 5,6-dihydroimidazo[5,1-a]iso-quinoline-1-carboxylate and methyl 5,6-dihydroimidazo[2,1-a]isoquinoline-3-carboxylate were determined by X-ray crystallography. 相似文献
88.
MingTaoLIANG DeXinWANG 《中国化学快报》2002,13(3):199-200
Some dehydropeptide analogues were directly synthesized by the reaction of unsaturated oxazolones with free amino acids. 相似文献
89.
Antonio Alberola 《Journal of organometallic chemistry》2007,692(13):2750-2760
Dithiazolyl radicals with π-stacking motifs have attracted particular interest because of their ability to exhibit spin-switching between diamagnetic distorted π-stacks and paramagnetic regular π-stacked structures through a solid state phase transition. Previous studies indicate that inclusion of electronegative heteroatoms into the backbone favours lamellar structures. This methodology has been extended to the synthesis and characterisation of the title compound, 4′-cyanobenzo-1,3,2-dithiazolyl (4-NCBDTA). Its electronic structure is probed through DFT calculations, cyclic voltammetry and EPR spectroscopy and its crystal structure determined by X-ray powder diffraction at room temperature. Variable temperature SQUID magnetometry reveals that 4-NCBDTA undergoes two phase transitions, each exhibiting bistability; a high temperature phase transition occurs at room temperature (TC↓ = 291 K, TC↑ = 304 K, ΔT = 13 K); whilst the low temperature phase transition occurs below liquid nitrogen temperatures (TC↓ = 37 K, TC↑ = 28 K;ΔT = 9 K). 相似文献
90.
The surface free energies of polyethylene terepthalate fibers with different draw ratios were experimentally determined by contact angle measurements inn-alkane/water systems. The dispersive component of the surface free energy increased with increasing draw ratio, whereas the nondispersive one remained almost constant. After heat treatment, the dispersive surface free energy increased, but was reduced above 140°C. The nondispersive component increased by heat treatment at 190°C. The increases in the density and birefringence of the fibres due to the drawing and heat treatment suggested that the increase in the dispersive surface free energy was caused by the increase in the atomic density at the fiber surface due to drawing and heat treatment. ESCA results indicated that the increment in the nondispersive surface free energy due to heat treatment was caused by the addition of functional groups to the fiber surface due to heat treatment. 相似文献