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Geometry of the theta divisor of a compactified jacobian
No full textThe object of this paper is the theta divisor of the compactified jacobian of a nodal curve.
We determine its irreducible components and give it a geometric interpretation. A characterization
of hyperelliptic irreducible stable curves is appended as an application
A compactification of the Universal Picard Variety over the Moduli Space of Stable Curves
No full text
Mechanism of stereocontrol in methyl methacrylate polymerization promoted by C-1-symmetric metallocenes
Full text linkThe mechanism of stereoselectivity in methyl methacrylate (MMA) monometallic polymerization promoted by the C-1-symmetric ansa-Me2C(CP)(Ind)Zr-based zirconocene, presenting two diastereotopic coordination sites, was investigated within density functional theory. At variance from the case of propene polymerization, our results suggest that MMA addition is stereoselective when the growing chain is in the more hindered as well as in the more open diastereotopic coordination site. In both cases the same enantioface of the enolate bond of the ester enolate growing chain is selected, although selectivity is higher when the growing chain is in the more hindered diastereotopic coordination site. Further, there is no substantial energy difference between these two situations, which indicates that the moderate isotacticity of the produced PMMA is consistent with an almost regular chain-migratory mechanism. The different stereoselectivity of the two diastereotopic sites is due to different steric interaction between the growing chain (chain effect) or MMA (monomer effect) with the indenyl ligand. This decomposition of stereoselectivity into chain and monomer effects is used to reinvestigate the stereoselectivity of strictly related C-2- and C-s-symmetric zirconocenes
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