Taft relationship slopes

The series 3-6 in Table II constitute a strong support for this approach to elimination mechanisms. The slopes of the Taft relationships p ) change with the nature of the catalysts and could be correlated with their other intensive properties, which were determined independently (Fig. 3). The... 

The structure effects on the hydrogenation rate of ketones also have been used for comparisons of catalysts. Simonikova, Ralkova, and Kochloefl 113) have pointed out that the slopes of the Taft relationships for series 91-93 for copper, platinum, and rhodium catalysts, together with the similar results of Iwamoto, Yoshida, and Anouma 112) for a nickel catalyst (series 90), exhibit an opposite trend from the d character of the metals. 

The broad applicability of LFERs for heterogeneous catalytic reactions has been demonstrated independently by Kraus (23) and Yoneda (24-27). The first author concentrated mostly on the established relationships such as the Hammett and Taft equations, whereas Yoneda has concentrated particularly on correlations with reactivity indices and other quantities. Since then, LFERs have been widely applied to heterogeneous catalytic reactions, and experience has been gained as to the suitability of each different type. An important step has been made toward an interpretation of the slopes of linear correlations (parameter a in Eq. 3) as the quantities that are closely connected with reaction mechanisms. 

Some information about structure effects on the rate of dehydrogenation of alcohols to aldehydes and ketones on metals is found in the older literature 129-132) from which it follows that secondary alcohols react more easily than the primary alcohols 129) and that the reactivity decreases with the length of the carbon chain 131). Some series can be correlated by the Taft equation using a constants (Ref. 131, series 103, Cu-Cr203 catalyst, 350°C, four points, slope 18 Ref 132, series 104, Cu catalyst, four points, slope 22). Linear relationships have been used in a systematic way by... 

Three main conclusions can be deduced from Fig. 15. One, the oxidation of all the monomers proceeds via the same mechanism as shown by their linear fit (with a slope of m = 0.80). The mechanism requires the removal of a tt electron from the aromatic thiophene unit. Two, the less electronegative the monomer, the more easily it will be oxidized as the substituent constant p has a positive sign. Three, substituents do not deviate significantly from a linear relationship, as can be directly observed from Fig. 15. Thus, the S term is not important. Therefore, the j8 substituents exert primarily an electronic effect, which is adequately described by the p a term in the Hammett-Taft equation. 

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