Hiickel wave formation

The electronic overlap populations in all three cases were calculated from the one electron Extended Hiickel MO s. For the photocyclizations of 1,2-difuryl ethylenes very similar results were obtained also from minimal basis set ab-initio wavefunctions l The possibility of obtaining useful reactivity analyses from wave-functions which are easily available even for large systems could prove to be an important practical consideration for further applications of this method. The dependence on Sri sj ill (5) ensures that electronic overlap populations show the desirable physical characteristics for their use as reactivity measures strong falling-off with increasing interatomic distance and proper directional dependence. This last point is of particular significance for bond formation in polyenes. Thus for two C 2 p atomic... 

The experimental observations on the mechanism(s) of electroreduction of 2-thio-pyrimidines have been interpreted on the basis of their electronic structures as calculated with the aid of the CNDO/2 and Hiickel procedures The energies of LUMO (lowest unoccupied molecular orbitals), calculated for pyrimidine and its 2-oxo-and 2-thioderivatives, were compared with the reduction half-wave potentials (Table V). These show that the presence of a carbonyl or thione substituent at Cj enhances the electron acceptor properties of the molecule, which are correlated with formation of a dimer susceptible to photooxidation. 

The oxidation of methylthio-substituted arenas in MeCN at a rotating Pt electrode was studied [82, 83], The half-wave potentials were found to correlate linearly with Hiickel HOMO energies, and the formation of cation radicals was judged to be reversible. 

The kinetics of formation and dissociation of Ni(SCN)2(aq) have been studied in water and in several organic solvents, using the pressure-jump and shock wave relaxation technique at 20°C. The concentration of Ni(SCN)2(aq) ranged between 0.001 and 0.1 M. In water, only the formation of the monothiocyanato complex was observed. No background electrolyte was used, and the activity coefficients were calculated by an extended Debye-Hiickel expression. Although, this activity model is not compatible with the SIT, the ionic strengths were low. Therefore, the reported result was corrected to 25°C and the resulting value was accepted with an increased uncertainty (log, = (1.79 0.10)). 

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