Hansch relationship

Optimum Correlation Equations. Table XI gives the final best-fit Hansch relationships which mathematically describe the pre-emergence herbicidal activity of the 3- and 4-substituted TFMS compounds under all conditions examined in this study. The results and conclusions reached... 

It is evident from the statistical tabulation in Table XI that the TFMS herbicidal data for Foxtail, Cheat Grass, and Wild Mustard are well-correlated by the given Hansch relationships, both in the presence and absence of surfactant. The numbers in parentheses beneath the fit parameter coefficients in Table XI are the standard errors in those coefficients. Perusal of Table XI leads to the following observations ... 

A more complete interpretation and comparison of the Hansch relationships in Table XI are given in the Discussion section. 

In view of the data presented, both questions can now be answered in the affirmative. The best-fit Hansch relationships in Table XI can be used to predict and to explain variations in TFMS grass and broadleaf activity. Furthermore, the appropriate equations in Table XI can be used... 

Except for the Hansch relationship of Figure 3d which exhibits no dependence on a, all other Hansch relationships in Table XI have a fairly large, positive a coefficient. Hence, the value of the pa term will increase in a positive fashion with increasing a in all of these latter equations. With respect to the corresponding plots of Figures 2-4, this means that... 

One point should be clarified with reference to the plots of Figures 2, 3, and 4 and the Hansch relationships in Table XI. The appropriate equations and plots describing TFMS herbicidal activity in the absence... 

As an illustration of the use of the final Hansch relationships in Table XI in explaining biological activity differences between individual TFMS series members, we will examine the activity of 4-S02CH3-TFMS and 4-C1-TFMS against Foxtail, Wild Mustard, and Cheat Grass. Table XIII gives values of the individual terms in the Hansch equations of Table XI which are appropriate to the action of each herbicide on the three weed types. At a later point, we also examine the activity of 2,4-di-Cl- and 2,4-di-F-TFMS derivatives as predicted by the Hansch relationships in Table XI. 

Thus, term-by-term analysis of the Hansch relationships derived for each TFMS series in the presence and absence of Tween 80 (coupled with perspective plots of the corresponding herbicidal activity surfaces) permits one to account for activity differences between species in a fairly detailed though empirical manner. Indeed, whereas Trepka and coworkers (5) found it difficult to account for grass and broadleaf selectivity differences of the 4-C1- and 4-S02CH3-TFMS derivatives in a straight-... 

Di-Cl—TFMS and 2,4-Di-F-TFMS. Trepka et al. (5) found the 2,4-di-Cl— and 2,4-di-F—TFMS derivatives to be highly active against both grasses and broadleaves (see Table I). We may thus ask whether the appropriate Hansch relationships listed in Table XI for the mono-substituted TFMS derivatives can be used to predict the high activity of these disubstituted compounds. 

Using these Xtt and So- values in conjunction with the first, fifth, and ninth para Hansch relationships in Table XI, the grass and broadleaf activity in the absence of Tween 80 for the two disubstituted derivatives can be predicted as follows ... 

Hansch relationships satisfactorily predict the high grass and broadleaf... 

The above treatment demonstrates the utility of the Hansch relationships of Table XI in predicting the grass and broadleaf activity of several disubstituted TFMS compounds. It also demonstrates the dangers in-... 

Item d implies that in terms of the Hansch model of Equation 1, partitioning STEP 1 is the primary rate-controlling process characterizing the herbicidal action of the 3-TFMS compounds on Wild Mustard in the presence of Tween 80. Since all the other Hansch relationships in Table XI include fairly significant pa contributions, partitioning as well as other rate processes (possibly more intimately connected with the receptor site within the plant or seed) must be involved in determining overall herbicidal activity in these latter cases. One may speculate that the anomalous observations (a-c) above are the direct consequence of (d)—the lack of Hammett a dependence. If the pa term in the Hansch equation does indeed reflect rate or equilibrium events occurring at or near the herbicidal site of action within the plant or seed (as is often assumed but not... 

Methylthio-TFMS derivatives (3-SCH3-TFMS, 4-SCH3-TFMS) exhibit anomalous behavior and may be oxidized in vivo to methylsulfinyl (-SOCH3) or methylsulfonyl (-S02CH3) before reacting at the receptor site within the plant or seed. Alternatively, they may function by a mode of action different from the other TFMS pre-emergence herbicides tested. The parent TFMS (H-substituted) appears to function as a 4-substituted series member rather than as a 3-substituted derivative. The predictive capabilities of the derived Hansch relationships were demonstrated for several specific cases. 

Equations (51) and (55)). This suggests that many experimental results published in the literature should be revised especially in the anomalous cases. The new definition of partition constant will also modify the contribution of polarizability to the Hansch relationship in pharmacological chemistry [73],... 

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