Experiment 4.6 Substitution Kinetics I—Determination

EXPERIMENT 4.6 SUBSTITUTION KINETICS I—DETERMINATION OF THE RATE OF FORMATION, kF, FOR THE REACTION BETWEEN [Fe(CN)5(H20)]3 AND AMINO ACIDS 

This experiment involves advanced theory of kinetics and mechanism. 

Continuing with this system, consider the anation reaction of the aqueous intermediate, [Co(NH3)5H20]3+, equation (4.10). This step is also expected to be dissociative in nature. Experimentation shows, however, a surprising dependence on the incoming Y the rate = kf [Co(NH3)5H203+][Y-]- How can we account for this dependence on Y- There are several possible mechanisms  

An Ia mechanism with direct attack of Y on the octahedral complex, equation (4.10). 

A D mechanism involving a preequilibrium with a five coordinate intermediate, equation (4.11). When fc2[Y ] k-i, a dependence on Y will be seen. 

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