Hiickel calculations species

Another type of interaction is the association of radical ions with the parent compounds. Recently (118), a theoretical study was reported on the interaction of butadiene ions with butadiene. Assuming a sandwich structure for the complex, the potential curve based on an extended Hiickel calculation for two approaching butadienes (B + B) revealed only repulsion, as expected, while the curves for B + and B + B" interactions exhibit shallow minima (.068 and. 048 eV) at an interplanar distance of about 3.4 A. From CNDO/2 calculations, adopting the parameter set of Wiberg (161), the dimer cation radical, BJ, appears to be. 132 eV more stable than the separate B and B species, whereas the separate B and B species are favored by. 116eV over the dimer anion radical, BJ. This finding is consistent with experimental results formation of the dimer cation radical was proved in a convincing manner (162) while the attempts to detect the dimer anion radical have been unsuccessful. With other hydrocarbons, the reported formation of benzene dimer anion radical (163) represents an exceptional case, while the dimeric cation radical was observed... 

In each case, we use program spece8 or react and employ an extended form of the Debye-Hiickel equation for calculating species activity coefficients, as discussed in Chapter 8. In running the programs, you work interactively following the general procedure ... 

The catalytic activity of the mixed-bridged dinuclear complex [Rh2( i-pz)(/ -S-f-Bu)(CO)2 P(OMe)3 2], 111, in the selective hydroformylation of 1-hexene to afford the corresponding aldehydes was explored and the results were compared with those observed for the symmetrical pyrazolate-free precursor [Rh2(CO)2(ft-S-f-Bu)2 P(OMe)3 2] (117, 212). Very mild conditions (5 bar, 80°C) were chosen in both cases. Complex 111 exhibits lower activity however, the selectivity is about the same as for the symmetrical precursor ( 80% heptanal and 20% 2-methylhexanal). Complex 111 does not give rise to a detectable dismutation and was found to be practically unchanged after reaction. A catalytic cycle in which all the intermediate species remain dinuclear was proposed for the hydroformylation of 1-hexene catalyzed by the symmetrical complexes [Rh2(CO)2(M-S-f-Bu)2L2] [L = P(OMe)3, PPh3, P(OPh)3] (213). This proposal is based mainly on the results obtained by varying the phosphorus ligands and on extended Hiickel calculations carried out for several proposed intermediates. It is possible that Complex 111 could follow such a cycle (117). 

The kinetics of the hydrolysis of D-glucosyl, D-mannosyl, D-galactosyl, and L-fucosyl a- and 3-phosphates between pH 1-6 have been determined. For the mono-anionic species the /3-anomers were hydrolysed 3-7 times faster than the a-anomers. Extended Hiickel calculations have shown that the difference in enthalpy between cyclic AMP and acyclic related phosphate esters is due to larger net exothermic solvation enthalpy in the former, ascribed to extra stabilization of the products of hydrolysis, due to their ability to form more stable hydrogen bonds with water. ... 

A useful combination of theoretical and practical work sheds some light on how the central geometry change at the T-shaped species may come about in some cases. Extended Hiickel calculations indicate that there is a considerable barrier to isomerization of isolated T-shaped trans-[PdR2L] to the cis isomer, though when the R groups are poor donors, cis-trans isomerizations will be more facile than reductive eliminations. " ... 

Funabiki et al. have performed a Extended Hiickel calculation study on the relative stability of the probable catecholatoiron complexes [118]. 3,5-Dimethylcatecholato-(tetraammonium)iron(III) complexes are used for simplification. The results support the radical character of the catecholate ligand and suggests that the direct attack of free oxygen on aromatics, if it occurs, can be at the C-2 and C-6 positions from the side perpendicular to the aromatic plane. This parallels the two routes in Scheme 8 and path A in Scheme 9. In the model species of type 50, the most electrodeficient C-1 is favored over C-2 or C-6 for the attack by peroxide if importance is attached to the anionic character rather than the radical character of the peroxide. 

Energetic behavior of the metal d and nitrosyl jt levels on bending the M-N-O unit. Adapted from Reference [54], the extended Hiickel calculation refers to an iridium nitrosyl species. 

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