On the calculation of transition state activity coefficient and solvent effects on chemical reactions

Solvent effects, when the classical transition state theory (TST) holds, ca n be interpreted following the Bronsted equation. However, when calculating the activity coefficient of the transition state, gamma(not equal) it is i mportant to take into account that this coefficient is different from that of the precursor complex, gamma(PC). The activity coefficient of the latter is, in fact, that calculated in classical treatments of salt and solvent e ffects. In this paper it is shown how the quotients gamma(not equal)/gamma( PC) change when the reaction medium changes. Therefore, the conclusions tak en on the basis of classical treatments may be erroneous.