Two classical tools, the intermolecular stretching force constants of H-bonded complexes and the molecular electrostatic potential are used to propose a nucleophilicity index evaluated for a series of pyridines. The model is validated against kinetic data recorded for the aminolysis of S-methyl 2,4-dinitrophenyl thiocarbonate. (c) 2006 Elsevier B.V. All rights reserved.