Self exchange reactions

Figure C3.2.11. Log of the ET rate (A) against (l/s p-l/E ) for tire bis(biphenyl) cliromium self-exchange reaction. From 1341.

Eree energy curves for the self-exchange reaction between two rubredoxins (Rdi and Rd2) were generated from MD simulations [86,87]. 

Marcus and Hush have developed a theory, which bears their names, that relates the value of kj2 to the rates (ku and 22) of the self-exchange reactions of the two... 

There is a very special case for self-exchange reactions in which the left side of the equation is identical to the right side. Accordingly, there is no free energy change in the reaction, and the equilibrium constant ( fn) must be unity (Eq. 9.29). 

We conclude with a consideration of a few other cobalt self-exchange reactions. The reaction in Eq. (9.33) is faster than that involving the ammine complexes (Eq. 9.30) because the water is a weaker-field ligand than ammonia. Thus, the activation energy for the formation of the electronically excited states is lower, as is the change in Co-ligand distances in the two oxidation states. 

The reduced poly-[Fe(II)TPP] porphyrin site now finds itself next to a fresh poly-[Fe(III)TPP(X)] site one polymer lattice unit further into the polymer. An electron hopping - or self exchange - reaction can then ensue, repeatedly, in successive layers and sites ... 

The reaction amounts to a vectorically directed current in the sense of occurring down a concentration gradient of reduced poly-[Fe(II)TPP] sites emanating from the reducing electrode/polymer interface. The magnitude of the current clearly conveys information about the rate of the poly-[Fe(III)TPP(X)] - poly-[Fe(II)TPP] self exchange reaction. 

Esr spectroscopy has also been used to study pure solvent dynamics in electron self-exchange reactions (Grampp et al., 1990a Grampp and Jaenicke, 1984a,b). When the systems are not linked by a spacer (i.e. TCNQ- /TCNQ (TCNQ = tetracyanoquinodimethane), the homogeneous bimolecular rate constants /chom are given by (10), with fcA the association constant and kET... 

A. Insights into the Mechanism of the Tl3+/ Tl+ Self-Exchange Reaction VII. Electrochemical Electron-Transfer Reactions... 

The reorganization energy of a self-exchange reaction is denoted A(0) (from the fact that AG° = 0) and is an important quantity in the Marcus theory, where it can be shown that the activation free energy of a self-exchange reaction, AG(0), is equal to X.(0)/4. It is also possible to measure rate constants of self-exchange processes experimentally and thus get access to (0) via this relationship. 

This rules out, I would think completely, a dominant outer-sphere mechanism for that system, because the observed rate is just too fast to be compatible with this. The self-exchange reaction must almost certainly proceed most favourably via an inner-sphere mechanism. More data of this kind are evidently needed. 

The significance of these quantities is analogous to that for the activation parameters for homogeneous self-exchange reactions. Thus, AH equals the activation enthalpy for conditions... 

Relationships having the same form as eq 14 can also be written for the enthalpic and entropic contributions to the intrinsic free energy barriers (10). Provided that the reactions are adiabatic and the conventional collision model applies, eq 14 can be written in the familiar form relating the rate constants of electrochemical exchange and homogeneous self-exchange reactions (13) ... 

Also, the observed rates probably refer to outer-sphere pathways, and the rate constants for the corresponding homogeneous self-exchange reactions are available or can be estimated from rate data for closely related cross reactions (15). These h ex... 

Rate Constants and Thermodynamic Parameters for Selected Electrochemical Exchange and Homogeneous Self-Exchange Reactions at 25°C. 

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