Benzene derivatives, Yukawa-Tsuno

The Yukawa-Tsuno (YT) equation for 4-substituted benzene derivatives is approximately equivalent to the CR equation23,24. This observation has led to the development of a modified Yukawa-Tsuno (MYT) equation which has the form ... 

The Hammett equation traditionally combines 3-substituted and 4-substituted benzene derivatives into a single data set using the composite constants for the former and constants for the latter. This is justifiable only if p3 is equal to P4 (Ap 0). We have shown that this is generally not the case except when the geometry of XGY is comparable to that of the benzoic acids from which the and Op constants were defined. The Yukawa-Tsuno and related equations are based on the assumption that P3 is equal to p4 and are limited to applications in which this is at least approximately correct. They are briefly reviewed elsewhere. ... 

The magnitude of p is in accord with a reaction at a ring C atom. Winkler and Winkler have also reported equilibrium and rate constants (sets CR7 and CR8, Table 9). We described above a modified Yukawa-Tsuno (MYT) equation (equation 6) with a taking the value for 3-substituted benzene derivatives and <750 for 4-substimted benzene derivatives, while for substituents in the meta position is 0. For this application the appropriate value of was unknown and all three pure electrical effect parameters were used for the para substituents thus the MYT equation used was equation 37 ... 

Yukawa-Tsuno equation A multiparameter extension of the Hammett equation to quantify the role of enhanced RESONANCE effects on the reactivity of meta- and para-substituted benzene derivatives, for example,... 

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