Delocalization parameters

The pi delocalization parameters of Table XXVII show X=p /p/ values which generally follow the classical sequence > X". There are several... 

In recent years Pagani and coworkers have made detailed studies of the problem. In the space available we can only outline their work and interested readers should consult the very detailed papers. The authors have developed special scales of substituent constants for dealing with contiguous functionalities 193. These new substituent constants are a (which seems to be related fairly closely to the ordinary a ), aIB (which bears some relationship to o/, but not that close), and (Tr-, a special delocalization parameter. It is claimed194 that these scales are appropriate for describing interactions between contiguous functionalities, as opposed to literature values which account for remote interactions . Various C—H acidities in gas phase and in solution were successfully correlated by means of multiple regressions on am and chemical shifts for the central carbon in the carbanions. 

A model was adopted in which the delocalizing power of the substituent was defined analogously to Fischer s increments (Fischer, 1964) and Arnold s o -scale (Arnold, 1986). Experimental delocalization parameters S"P were calculated according to (10). By definition, 5 is zero for the... 

Table 6 Delocalization parameters for a-substituted benzyl radicals CjHjCXY."...

Table 1 Energies and delocalization parameters for selected tautomers of m-ben-ziporphyrin (147c) and m-benziporphyrin (150c), and m-benziphlorin (148c)...

Here we have allowed the delocalization parameter in the broken symmetry state, B, to differ from that in the high spin state the Xa results reported below show that this indeed happens. Eigenvalues for the broken symmetry case are E 2 -(25/4)J 5B and E3 = -(15/4)J. 

Membrane potential and pH gradient are always determined separately. Since a membrane potential is a delocalized parameter for a given membrane, it follows that the membrane potential generated by the translocation of protons across the membrane will be felt by all ions distributed across the membrane. If an electrical uniport pathway exists for one of these ions, then it will tend to come to an equilibrium when its electrochemical potential gradient is zero ... 

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