Electron localization-delocalization matrices in the prediction of pKaʹs and UV-wavelengths of maximum absorbance of p-benzoic acids and the definition of super-atoms in molecules

An integration of chemical graph theory and the quantum theory of atoms in molecules (QTAIM) is proposed. QTAIM localization and delocalization indices organized as matrices are shown useful in the modeling of ground and excited state molecular properties. The pKaʹs of 14 para-substituted benzoic acids and the λmaxʹs of a subset of those are predicted with accuracy (pKa: r2 = 0.986, q2 = 0.982; λmax: r2 = 0.973, q2 = 0.944). ‘Super-atoms’ obtained by pruning the branches of the substituents’ graphs equalize the matrices of all molecules of the set. The pKa of p-dimethylaminobenzoic acid is found to be 5.02 rather than the reported value of 6.03.