Kinetics analysis of the idealized heavy hydrocarbon system comprising a reactant A1 = μ1H converting through a Rice-Herzfeld chain in the presence of a chain transfer solvent A2 = μ2H revealed the conditions and structural features of A2 for optimal rate enhancement E = r_(A1)(A1, A2)/r_(A1)(A1) = (1 + κSθ)/(1 + κS), where κ= k_(12)/k_(21) is the index of chain transfer and θ = k_(21)/k_(11) is the index of the kinetic effect of chain transfer. Imposition of the Evans-Polanyi relationship for these two hydrogen abstraction reactions rendered E a function of the μ2-H bond strength x for a given reactant A1. Qualitatively, κ decreases and θ increases with increasing values of x. For low values of S, the intuitive optimum is where the balance between these two dependencies is found. For higher values of S, the optimal value of x is defined by the condition dθ/(θ-1) = dκS/(κS(1+ κS)).
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