Hammett substituent constants for

Linear correlations between l(L) and Hammett substituent constants for substituted jr-cyclopentadienyl and 7r-arene ligands [69], for other substituted Kgands,... 

Quantitative relationships have been reported between the global electrophilicity index and the experimental rate coefficients for the reactions of thiolcarbonates and dithio-carbonates with piperidine. The validated scale of electrophilicity was then used to rationalize the reaction mechanisms of these systems. This scale also makes it possible to predict both rate coefficients and Hammett substituent constants for a series of systems that have not been experimentally evaluated to date.48... 

Table 2.2 Hammett substituent constants for some substituents...

A correlation has been made between the Hammett substituent constants for 9-substituted benzo[h]quinohzinium salts and the rate of cycloaddition113 this, and the measured Arrhenius parameters for the same... 

Benzoic acids containing electron donating substituents will have smaller Kx values than benzoic acid itself and hence the value of ax for an electron donating substituent will be negative. Substituents such as Me, Et, and Bu1 have negative a values. The Hammett substituent constant for H will be zero. 

More recently Zhu, Wang, and Liang [498] have used DFT and PCM cluster-continuum computations to estimate oxidation potentials, bond dissociation energies, and pK s of 118 hydroquinones and catechols in DMSO. The pK s and other properties were also found to correlate well with the Hammett substituent constants for the compounds. 

A linear correlation was found between the binding energies and the sum of the Hammett substituent constants for X-TAZ---Y complexes. Linear dependences between electron densities at BCP and the appropriate interatomic distances are satisfied, but the slopes of these lines are different, indicating variable sensitivity of the noncovalent interactions to the substituent effects (see Figure 6). 

Although the FMMF method dramatically reduces the number of substituent constants that one must consider, it suffers from the disadvantage that it is not possible to visually compare two reactions with a three-parameter equation, i.e., one cannot simply plot logs of rates or equilibrium constants against a single parameter as one does in the normal Hammett treatment. It is possible, however, to calculate Hammett substituent constants for any position using the FMMF parameters and the following relationship ... 

TABLE 1. Selected Hammett substituent constants, for silicon-based substituents resonance and field parameters... 

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