LArSR equation

The Yukawa-Tsuno relationship expanded to include both the [Pg.210]

Relative activation enthalpies (Aif) in Table 2 were converted to o% kx k ) at 298 K, and were plotted against Hammett a constants. Here, we used enthalpies, because the size of the entropy and hence the free energy depend much on low frequencies, which are less reliable than higher frequencies, especially for compounds with weak interactions such as TS (8). The use of free energy (AG ) gave similar correlations with more scattered points. As for the Hammett o constant, we used dual-parameter o constants in the form of the Yukawa-Tsuno equation (LArSR equation) (9) as defined in eq 3. Here, the apparent a constant (aapp) has a variable resonance contribution parameter (r), which varies depending on the nature of the reaction examined for t-cumyl... 

Yukawa, Tsuno and their colleagues121 have made studies more specifically related to determining substituent constants, which have included both methylsulfinyl and methylsulfonyl groups. Hydroxyl chemical shifts were determined for a large number of m-and p-substituted phenols in DMF and in DMSO. The results were treated by the LArSR relationship121 (usually called the Yukawa-Tsuno equation, see Section II.B) ... 

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