
TY  - JOUR
A1  - Linert, W 
A1  - Schmid, R 
A1  - Kudrjawtsev, AB 
T1  - Concerning the Problem of the Isokinetic Relationship. III. The Temperature-Dependance of the hammett Equation
JF  - Australian Journal of Chemistry
JO  - Aust. J. Chem.
Y1  - 1985
VL  - 38
IS  - 5
SP  - 677
EP  - 688
KW  - 
UR  - https://doi.org/10.1071/CH9850677 
N2  - It is shown that the temperature-dependence of the Hammett equation is, in contrast to tradition, both physically and experimentally better described by means of temperature-dependent &#963; and temperature- independent &#961; (termed &#961;o). The relationship between &#961;o and the customary (temperature dependent) &#961; is           &#961;T = &#961;o(1/T-1/Tbiso)/(1/T-1/Tbiso) where Tbiso , is the isoequilibrium temperature of the benzoic acid ionization, for which the present analysis suggests a value of -255 K, and T is 298 K. In these terms, the temperature variation of the Hammett equation can be evaluated by supplying merely E(u)a (the activation energy for the reaction of the unsubstituted reactant) and &#961;o, in that the &#963; value for the isokinetic  substituent , i.e., the abscissa of the common point of intersection in the Hammett plot, is        &#963;iso = (1/T-1/Tbiso)E(u)a/(2.303R&#961;o) = E(u)a/(2630po) Further, &#961;o I  related to energies &#961;o = E(u)a/(&#916;H&#176;u-&#916;H&#176;s(iso))where &#916;H&#176;u and &#916;H&#176;s(iso) are the ionization enthalpies of the parent benzoic acid and that bearing the isokinetic substituent , respectively. Analogous equations apply to thermodynamic reaction series when substituting E(u)a for &#916;H&#176;u(series). Along these lines the interpretation of the customary Hammett plot is advanced. 
ER  -

