Electronic parameters in QSAR

The distribution of electrons within a molecule depends on the nature of the electron withdrawing and donating groups found in that structure. Hammett used this concept to calculate what are now known as Hammett constants (try) for a variety of monosubstituted benzoic acids (Equation (4.5)). He used these constants to calculate equilibrium and rate constants for chemical reactions. However, they are now used as electronic parameters in QSAR relationships. Hammett constants (crx) are defined as ... 

The advent of molecular graphics and other facets of computational chemistry has led to an increased use of steric and electronic parameters in QSAR studies, and these quantities can now be calculated more precisely and... 

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