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991.
The stereoisomeric equilibrium composition over Pd/C at high temperature of a series of tetracyclic saturated hydrocarbons having general formula C18H30 was determined by gas chromatography and compared with that calculated on the basis of conformational analysis. Several stereoisomers were isolated. Their 13C NMR spectra agree very well with those calculated according to standard procedures. This method of structural determination was applied to perhydronaphthacene, perhydrobenzo(a)anthracene, 2- and 5-methylper-hydrobenzo (d,e)anthracene and 2,7-dimethylperhydropyrene. 相似文献
992.
Vito Di Noto Lucia A. Magrì Maria Viviani Carla Marega Antonio Marigo Roberto Zannetti 《Journal of chemical crystallography》1992,22(1):59-64
FT-IR Spectroscopy with total attenuated reflectance (ATR) was used for the quantitative determination of ethyl formate coordinated in inorganic matrices such as magnesium chloride. The spectra were recorded directly on solutions obtained by dissolving the inorganic Ziegler-Natta supports in water. The method proposed is sensitive and rapid and appears to be very reliable when compared with other methods, such as solvent extraction followed by gaschromatographic or thermogravimetric analysis. 相似文献
993.
Clarissa O. da Silva André Gustavo H. Barbosa Emerson T. da Silva Edson Luiz L. da Silva Marco Antonio C. Nascimento 《Theoretical chemistry accounts》2004,111(2-6):231-236
In order to better understand the performance of 1,2-dimethyl-5-acetyl barbituric acid (DMB) as an amino protecting group relative to 5,5-dimethylcyclohexane-1,3-dione (DMD), ab initio calculations were performed. pKa calculations using the PCM model indicated that both molecules are more acidic in the enol form. Therefore, the protecting reaction of these molecules should involve the anions formed from the loss of a proton from the enol compounds. Contrary to what would be expected, the larger efficiency exhibited by the DMB molecule cannot be attributed to an extension of the electronic conjugation effect. In the absence of any other noticeable effect that could be responsible for the greater efficiency of the DMB molecule, we are inclined to believe that the difference could be accounted for by the presence of two independent centers of conjugation.This paper is dedicated to Jacopo Tomasi in recognition of his outstanding contribution to the field of computational chemistry in solution. The authors are honored to contribute to this volume; especially so for two of them (COS and MACN) who have the privilege of his friendship.Acknowledgements The authors would like to thank the Brazilian research agencies CNPq, CAPES and FAPERJ for the financial support. C. O. da Silva thanks the Dipartimento di Chimica e Chimica Industriale, University of Pisa, where the MCSCF calculations were performed. 相似文献
994.
995.
996.
Misbahul Ain Khan Antonio Carlos Carreira Freitas 《Journal of heterocyclic chemistry》1983,20(2):277-279
A number of 1, 5′-bipyrazoles were obtained from the condensation of pyrazol-5-ylhydrazine and 1, 3-dicarbonyl compounds. Electrophilic substitution reactions of these 1, 5′-bipyrazoles occur at the four position of the pyrazole ring. 相似文献
997.
Angelo Crugnola Antonio Longo Ferruccio Casabuona Paolo Lombardi 《Tetrahedron letters》1981,22(41):4141-4144
The synthesis of chiral “4,7-lactam“ has been accomplished starting from natural 6-aminopenicillanic acid. 相似文献
998.
999.
Summary When two immiscible fluids in a porous medium are in contact with one another, an interface is formed and the movement of
the fluids results in a free boundary problem for determining the location of the interface along with the pressure distribution
throughout the medium. The pressure satisfies a nonlinear parabolic partial differential equation on each side of the interface
while the pressure and the volumetric velocity are continuous across the interface. The movement of the interface is related
to the pressure through Darcy’s law. Two kinds of boundary conditions are considered. In Part I the pressure is prescribed
on the known boundary. A weak formulation of the classical problem is obtained and the existence of a weak solution is demonstrated
as a limit of a sequence of classical solutions to certain parabolic boundary value problems. In Part II the same analysis
is carried out when the flux is specified on the known boundary, employing special techniques to obtain the uniform parabolicity
of the sequence of approximating problems.
Entrata in Redazione il 29 novembre 1975.
This research was supported in part by the National Science Foundation, the Senior Fellowship Program of the North Atlantic
Treaty Organization, the Italian Consiglio Nazionale delle Ricerche, and the Texas Tech. University. 相似文献
1000.