Delocalization energy of activation

As we have seen (p. 205), the relative rates of a series of related reactions are determined by the corresponding changes in the delocalization energy of activation i e., the difference in delocalization energy between the... 

The -cis and -trans conformations of 1,3-butadiene interconvert by rotation around the C-2—C-3 bond, as illustrated in Figure 10.5. The conformation at the midpoint of this rotation, the perpendicular conformation, has its 2p orbitals in a geometry that prevents extended conjugation. It has localized double bonds. The main contributor to the energy of activation for rotation about the single bond in 1,3-butadiene is the decrease in electron delocalization that attends conversion of the 5-cis or i-trans conformation to the perpendicular conformation. 

The hypothesis that aromatic reaction rates are controlled by the ring destabilization step can be tested by comparing the rates of hydro-genolysis and pyrolysis. If true, the rates of decomposition of a given aromatic compound should be identical for either process. Further, reaction rates and their associated activation energies should correlate with the delocalization energy of that compound. Sources of experimental information for the aromatic compounds of interest are listed in Table II along with associated reaction conditions. In each case, the data were processed by the usual methods to yield first-order rate constants (ku sec"1) as a function of temperature for the initial decomposition of the aromatic ... 

This effect is readily attributable to the very loose structure of the ion-pairs in the TS (also involving delocalization in the phenyl groups of the phosphine) and which are therefore far more polar than the initial ion-pairs in the GS. Furthermore, because tetraalkylammonium is a poor leaving group reacting under rather harsh conditions (high energy of activation), we are certainly concerned with a late TS very prone to MW effects. 

The delocalization energy of two active regions AEi and AE2 The number of detoxification region n... 

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