Most of polymerization reactions with Ziegler catalysts operate through the ‘non-living’ mechanism, whereas lanthanide catalysts show a living-mechanism character. The degree of ‘livingness’ in a polymerization reaction is generally investigated through kinetics and the product analysis rather than by direct analysis of a catalyst. We have developed a new insight for judging the ‘livingness’ in polymerization reaction in aspect of electronical properties of the active chain ends of Li, Ni and Nd catalysts for 1,3-butadiene polymerization using the frontier orbital analysis. The frontier orbitals of the Ni catalyst are different from those of the Li and Nd based catalysts. The HOMO of the Ni catalyst has mostly the d-orbital (Ni) character while the LUMO has the p-orbital (Cα and Cγ atoms) as well as the d-orbital (Ni) character. The π-butenyl coordination at the Ni catalyst is η1-type but those of the Nd and Li catalysts are η3. The atomic charge (+0.003) on the Ni atom and the atomic charge (−0.14) on Cα of the Ni catalyst are much lower than those of the Nd catalyst (Nd +1.09, Cα −0.56). 相似文献
Most of the coumarins have been found useful as non-linear optical chromophores. The four novel water-soluble coumarin-based compounds (OC6, NC6, OC7, and NC7) and the metallic compounds of NC7 with different metal cations (Na+, K+, Mg2+, Ca2+, Fe2+, and Zn2+) have been investigated by carrying out density functional theory (DFT). Our DFT calculations revealed that the second-order nonlinear optical properties have a pronounced enhancement by means of the introduction of π-conjugatd electron donor (dimethylamino phenyl alkynyl) in 7-position of the coumarin ring and metal cations, especially for transition metals. The further investigations of the larger first hyperpolarizability (βtot) reveal that the NC7*Fe2+ and NC7*Zn2+ present the larger values as 1.151 × 10−27 and 1.083 × 10−27 esu owing to the lower transition energies and larger oscillator strengths of crucial electronic transitions. Moreover, time-dependent DFT results show that the large intramolecular charge transfers exist in the NC7*Fe2+ and NC7*Zn2+. In addition, the natural bond orbital analysis demonstrated that the second-order stabilization energies is from the lone pair (LP) orbital on O atom to the LP* orbital of metal cations interaction correlate with the O-Mn+ atomics distance. On the other hand, the atoms in molecules analysis showed that the O-Mn+ interactions can be characterized by the presence of a bond critical point (BCP) and the O-Fe2+ and O-Zn2+ interactions have partially ionic and partially covalent bonds rather than an electrostatic character for O-Mn+ (Na+, K+, Mg2+ and Ca2+). In addition, the delocalization indices of O-Mn+ bonds correlate reasonably well with electron density, kinetic and potential energy densities in these complexes. Thus, we hope this research will introduce a new relation between the structure and the property of chromophore nonlinear optical activity. 相似文献
This paper evaluated the COD, TOC removal and molecular frontier energies in the ozonation of naphthalene sulfonic acids (NSAs). It was found that both COD and TOC degradation of the 11 compounds followed the pseudo-first-order kinetic and the reaction rate constants with ozone varied widely. A linear relationship between logarithm of global COD degradation rate constant and the energy of the highest occupied molecular orbit, E(homo), was obtained for these NSAs with a regression coefficient of 0.88 and a slope of 0.4672 eV(-1). TOC degradation kinetics also reached similar results with a regression coefficient of 0.90 and a slope of 0.9336 eV(-1). The results of correlation analysis suggested that TOC and COD removal in ozonation of NSAs follow the frontier orbital theory and can be predicted by E(homo), which indicated that electrophilic effect was the main factor in the ozonation of NSAs. Therefore, it is possible to improve the biodegradability of dyestuff wastewater bearing mainly NSAs by ozonation at an accepted cost and evaluate the economy of ozonation process. 相似文献
In this work, we describe the use of Boron Dipyrromethene (BODIPY) as electron‐withdrawing group for activation of double bonds in asymmetric copper‐catalyzed [3+2] cycloaddition reactions with azomethine ylides. The reactions take place under smooth conditions and with high enantiomeric excess for a large number of different substituents, pointing out the high activation of the alkene by using a boron dipyrromethene as electron‐withdrawing group. Experimental, theoretical studies and comparison with other common electron‐withdrawing groups in asymmetric copper‐catalyzed [3+2] cycloadditions show the reasons of the different reactivity of the boron dipyrromethene derivatives, which can be exploited as a useful activating group in asymmetric catalysis. Additional experiments show that the so obtained pyrrolidines can be employed as biocompatible biosensors, which can be located in the endosomal compartments and do not present toxicity in three cell lines.
