Cleavage reactions formation kinetic parameters

The kinetic parameters for the bridge cleavage and formation reactions show a number of trends which in some cases parallel those... 

The previous analysis shown that the initial values of most of the kinetic parameters obtained from DFT calculations provide a good description of the reaction kinetics data collected over a wide range of conditions. The principal difference between the values of the final kinetic parameters used in the model and the initial values obtained from DFT calculations is that the fitted enthalpy changes for the formation of C2Ha transition states involved in cleavage of the C-C bond are lower than the initial values predicted from DFT calculations. This difference may be explained by the structure sensitivity of the system and/or by the inherent error of the DFT calculations. 

SCN-, or F ) has been studied using acidic perchlorate media. The rhodo ion yields Cr(NH3)5(H20)3 +, whereas the erythro ions yield both Cr(NH3)5(H20)3+ and the respective cis or trans isomers of Cr(NH3)4(H20)X(3 M,+. The kinetic data are consistent with a contribution from the uncatalyzed path (k0 in Scheme 3) alone, and yield the parameter values listed in Table XXV. Bond rupture in the unsymmetric species is assumed to occur at the Cr(NH3)4X fragment, since, when trans chloroerythro is cleaved in the presence of Cl- or Br, the halide is incorporated into the tetraammine fragment while the pentaammine fragment remains as Cr(NH3)5(H20)3+ (252). The cleavage of the cis aquaerythro ion in the presence of Cl- and Br-, respectively, has been studied (254), and both systems follow the rate law — d[dinuclear]/d< = (kx + A2[X])[dinuclear], where X = Cl- or Br-. In the reaction with chloride the products are Cr(NH3)5(H20)3 + and cis-Cr(NH3)4Cl(H20)2 +, and the formation of cis chloroerythro as an active intermediate was proposed. In contrast to this, the products in the bromide reaction are Cr(NH3)5(H20)3+ and cis-Cr(NH3)4(H20)23+. The enhancement of the cleavage rate by bromide has been explained in terms of ion-pair formation. 

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