Molecular reorganization processes

Recently, Wilsey and Houk introduced a new detailed molecular reorganization process that more specifically describes the HT process and successfully accounts for formation of the observed products. It involves pyramidalization of a carbon and its bridging of the attached vinylic hydrogen with the adjacent carbon (in analogy with the minimized structure of excited ethene) for the Cl structures of excited butadiene. They argued that pyramidal inversion of such a Cl structure leads to the stereochemical consequence of HT. 

The largest values for the standard rate constant k° (expressed in metre/second) range from 0.01 m s-1 to 0.1 m s-1, and commonly characterize redox processes which do not involve significant molecular reorganizations. 

As often underlined, one of the main targets of the electrochemical investigations on inorganic compounds is to ascertain their stability upon addition or removal of electrons. However, should the compounds undergo important molecular reorganizations as a consequence of such electron transfer processes, it is also important to ascertain the nature of such redox changes. 

Fig. 7. Principle of the electrochemically induced molecular motions in a copper(I) complex pseudorotaxane. The stable four-coordinate monovalent complex is oxidized to an intermediate tetrahedral divalent species. This compound undergoes a rearrangement to afford the stable five-coordinate copper(II) complex. Upon reduction, the five-coordinate monovalent state is formed as transient. Finally, the latter undergoes the reorganization process that regenerates the starting complex [the black circle represents Cu(I) and the white circle represents Cu(II)]...

Whether CT is possible depends on the polarity of the solvent, as measured by the dielectric constant. There are essentially two important dielectric constants one for slow processes or the static dielectric constant (Cj) and the other for very fast processes (faster than any reorganization process), referred to as or the dielectric constant at infinite frequency. of a compound can be obtained by measuring the capacitance of a condensator where the compound is used as a dielectricum. is obtained by measuring molecular polarizability. The higher the frequency of the applied electric field, the slower are the motions in the medium to follow the variations in the field. For example, a water molecule has a certain rotation time and when the field frequency is too fast, the water molecule no longer moves with the field. When the frequencies applied correspond to UV frequencies, (for all practical purposes) is measured. One may show that = n, where n is the refractive index. 

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