Eyring parameters exchange

TABLE 6. Eyring activation parameters for allyhc exchange in allyl Grignards... 

The measurement of the exchange time xm may provide useful kinetic information on the system. Kinetic parameters for the dissociation process may be obtained by performing relaxation measurements as a function of temperature. If it is assumed that the dissociation of the ligand from the paramagnetic site is a first order kinetic process, the dissociation rate constant r 1 is given by the Eyring relationship... 

Most frequently dynamic NMR measurements are carried out in order to obtain activation parameters which are calculated from the temperature dependence of the exchange rates estimated from the spectra. The Eyring equation is usually employed to draw a straight line according to the least-squares fit ... 

The resulting three coupled density matrix equations 61 are solved for the required density matrix elements which are summed (equation 10) to give the 13C NMR line shapes. A similar procedure provides the 13C NMR line shapes for carbon bound 7Li. Comparison of observed and calculated NMR line shapes provides the Eyring activation parameters for bimolecular C—Li exchange listed in Table 13. 

Band-shape analysis can be a powerful mechanistic tool, affording exchange rates, from which activation parameters can be derived via Arrhenius and/or Eyring plots. Thus, possible exchange/reaction mechanisms can be distinguished. Care, however, is needed since ... 

Kinetic parameters for the amide f-H— 2H exchange for several ferrichrome analogues dissolved in D2O, pD 5.14 (59). The data are for the Al3+ chelates except in (a) where it refers to the Ga3+ complex of deferriferrichrome ( gallichrome ). AHt and ASt are the activation enthalpy and entropy values, respectively, as estimated from Eyring plots. AFt (25) and ti/2 (25) are the activation free energy and the reaction half time calculated from the AHt and ASt data at 25 °C. 

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