ABSTRACT
Conversely, when the proton transfer rate is considerably faster than the backward electron transfer, the RDS is the forward electron transfer and the observed rate constant is then kr, as given in Eq. (46):
(46) It is thus seen that, in the first situation, although the thermodynamic interdiction
has been overruled, thermodynamic figures control the apparent rate constant observed. Indeed, Eq. (45) may be rewritten as in Eq. (47):
(47) Thus owing to the large magnitude of kH(103 - 106 M-1 s-1 [36b---c,38,40]), the rate constant in Eq. (47) remains appreciable even for largely endergonic electron transfers (for 1,2,4,5-tetramethylbenzene, Epe - m,rCH, < -0.6 V). Yet if the electron transfer is too endergonic, kap becomes too small for the reaction to proceed at a significant rate.
