THEORETICAL VERSUS EMPIRICAL MOLECULAR DESCRIPTORS IN MONOSUBSTITUTED BENZENES - A CHEMOMETRIC STUDY

Quantum chemical methods and molecular modeling techniques allow the definition of a large number of molecular and local quantities characterizing the reactivity, the shape and the binding properties of a molecule as well as of molecular fragments and substituents. This study is focused on a systematic comparison of the theoretical molecular descriptors with both empirical (Hammett's and Taft's substituent constants, hydrophobic parameter, Verloop's steric parameters etc.) and experimental (substituent induced chemical shifts, molecular weight and molecular refractivity) descriptors. Fifty selected monosubstituted benzenes, including some charged substituents have been computed in the AM1 framework. Several theoretical descriptors have been extracted from the AM1 electronic wavefunction as well as molecular modeling techniques and they have been analyzed by principal component analysis and the partial least squares method. The results obtained are consistent with previous principal component studies concerning empirical descriptors, and highlight the interdependencies among theoretical and empirical molecular descriptors.