Charton extended Hammett equation

A number of correlations of ionization potentials for substituted benzenes (40-42), benzyl (43), phenoxy (44), and alkyl (45) radicals and substituted pyridines (46) with the simple Hammett equation have been reported. Charton (47) has studied the application of the extended Hammett equation to substituted ethylenes and carbonyl compounds. The sets studied here are reported in Table II (sets 2-10 and 2-11). Results of the correlations are set forth in Table 111. The results obtained are much improved by the exclusion of the values for X = C2 H3, Ac, F, H and OAc from set 2-10 (set 2-lOA) and the value for X = H from set 2-11 (set 2-11 A). The composition of the electrical effect corresponds to that found for the Op constants as is shown by the pR values reported in Table IV. 

Ionization constants of czs-3-substituted acrylic acids have been correlated with the Hammett equation by Hogeveen (58) and by Charton (60). Charton has correlated ionization constants for a number of other c/s-vinylene sets with the Hammett equation (60). Charton and Charton have correlated some cw-vinylene sets with the extended Hammett equation [eq. (2)] (73). Sufficient data are available for twelve sets of cis-vinylene equilibria, of which four sets represent ionization constants of hydroxy compounds (sets 12-1 to 12-4) and eight sets represent ionization constants of carboxylic acids (sets 12-5 to 12-12). All sets have been correlated with eq. (24) and eq. (2). Sets studied are reported in Table XII. Results of the correlations are reported in Table XIII. Sets designated A were correlated with eq. (24), sets designated B were correlated with eq. (2). In the case of the second ionization constant of 2,3,5,6-tetrahydroxy-l,4-benzoquinone (set 12-3), it is uncertain which hydroxyl group ionizes therefore, the value for X = OH was excluded from the correlation. All of the sets 12-1 to 12-4 gave significant correlations with both eq. (24) and eq. (2),... 

Data for fra s-heterovinylene sets were first correlated with the extended Hammett equation by Charton and Charton (73). It must be noted that in frans-heterovinylene sets, the reaction sites and substituent are tram to each other. There are available in the literature data for three fraws-heterovinylene sets, all oximes. The sets studied are presented in Table XXVII (sets 27-1 through 27-3). Results of the codelations and values of are given in... 

Data for substituted cyclopropane rings can be conveniently arranged in five categories substituted cyclopropane sets, cyclopropylidene sets, trans-cyc o-propylene sets, cis-cyclopropylene sets, and reactions of cyclopropane rings. The correlation of data for cyclopropanes with the Hammett equation (19) and the extended Hammett equation (215) has been reported by Charton. 

A slightly different procedure for carrying out multiple regression on cr/ and og-type parameters employs the extended Hammett equation of Charton95, which may be written as in equation 9. For the substituent X, Q is the absolute value of the property to be correlated (logfc or logX in the case of reactivity), i.e. not expressed relative to X = H, h is introduced as the appropriate intercept term, and the regression coefficients are a and fi. (Charton has used various symbols at various times.)... 

Charton 152) has successfully applied the extended Hammett equation to these data and discussed the macroconstant, pA , in terms of the tautomerism... 

Charton (J52) has also applied the extended Hammett equation to the oxidation-reduction potentials of 5-substituted phenanthroline complexes of iron in various acidic media (95, 97, 651) and of bis-5- and 4,7-substituted phenanthroline complexes of copper in 50% dioxane (404). Thus, one should expect an overall similarity between the variations in pAa, stability constant, and oxidation-reduction potential data for the various ligands. The variations in a and )3 values found for various substitution positions and the tautomerism in the LH+ ions show that the correlation need not be good. A similar point may also be made about the comparison of data for the transoid bipyridylium ions and their cis complexes. Plots of A versus pA for various systems (95, 404) show a linear dependence to differing extents. As would be expected, the data for analogous complexes of iron (28), ruthenium (214, 217, 531), and osmium (111, 218, 220) show very good correlation. The assumption (152) that the effects of substituents are additive is borne out by these potential data, where the changes in potential on methyl substitution are additive (97). 

A slightly different procedure for carrying out multiple regression on aj d and cr/ -type parameters employs the extended Hammett equation of Charton, which may be written... 

This has been developed since 1986. The title letters stand for Localized Delocalized Response. The localized effect is Charton s preferred name for the inductive effect and delocalized effect is his preferred name for the resonance effect. Indeed, he would like to change the usual symbols from <7/ to 0/, and or to op for the purposes of the Extended Hammett (EH or LD) equation109. The response referred to is that of the substituent to the electronic demand of the site (i.e. reaction site in the correlation analysis of reactivity). Thus this equation, like the PSP equation, is concerned with the parametrization of substituent polarizability. 

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