Substitution approximation, electron-transfer

From the latter, it is seen that for n = 1 and room temperature, for example, E /2 shifts anodically by approximately 30 mV per unit of log k5 /D. As for the slow electron transfer case, Ei/2 is therefore not an acceptable substitute for E° since it incorporates kinetic contributions that then arise from the follow-up chemical reaction. 

They have compared the reaction energy profiles of five different reaction paths, including oxidative insertion, nucleophilic substitution, and single-electron transfer mechanisms involving radical species, both in the gas phase as well as using an electrostatic continuum model to include the effect of a solvent in an approximate fashion (Structures 3-5). 

Another example of self-assembly of porphyrin-containing polymer was illustrated by Li et al.73 Polyacetylene functionalized with fullerene and zinc porphyrin pendant groups were synthesized by polymerizing the corresponding fullerene/porphyrin substituted alkyne monomers with rhodium(I) norbomadiene catalyst (Scheme 5.5).74 Polymers with different ratio of C60 and porphyrin were synthesized. The polymers showed photocurrent response when the thin films were irradiated with white light, which was due to the electron transfer from the photo-excited porphyrin to the C60 units. In addition, the copolymers aggregated into ellipse-shaped nanorod structures with a diameter of approximately 100 nm and a length of... 

Rate constants for the reaction of substituted pyridines with the 4-methoxystyrene radical cations have also been measured (Table 6). The bulky 2,6-di-tert-butyl pyridine reacts with the two methyl-substituted radical cations with rate constants of approximately 10 M s , but is substantially less reactive towards 4-methoxystyrene. This reaction has been attributed to deprotonation since electron transfer would be endergonic by -0.7 V and since the effects of methyl substitution at the P-carbon are opposite to those observed for other nucleophilic additions. 2,6-Dimethylpyridine also reacts with the two methyl-substituted radical cations with rate constants of 10 M s, but is approximately I order of magnitude more reactive towards the 4-methoxystyrene radical cation. The latter reaction must be nucleophilic addition since this radical cation cannot undergo deprotonalion. Product studies have confirmed that the reaction of 2,6-dimethylpyridine with the p-methyl-4-methoxystyrene radical cation is deprotonation. The major product of irradiation of a mixture of 1,4-dicyanobenzene, 4-methoxystyrene, and 2,6-dimethylpyridine is the rearranged tautomer, 3-(4-methoxyphenyljpropene, formed by a deprotonation, reduction, protonation sequence as shown in Eq. 19. By contrast to these... 

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