The reactivities of a series of molecules in a Michael addition reaction are analyzed on the basis of properties expressed in the Laplacian of the charge density distribution. The charge densities of structurally optimized acrylic acid (AA), methacrylic acid (MAA), acrylonitrile (ACN) and acrolein (ACR) have been calculated by ab-initio quantum mechanical methods with various basis sets. The relative reactivities of the activated double bond in the molecules toward a nucleophilic attack, predicted by the values of Laplacian of the calculated charge density at the corresponding critical point, are in accord with experiment. The change in atomic properties of two reactants, AA and MAA, upon the nucleophilic addition of F(sup 1-) are also derived from the Laplacian of the charge density. The changes in the properties provide a quantitative description of AAF(sup 1-) and MAAF(sup 1-) carbanion formation which is related to the size of the region of charge depletion on the attacked atom. (Copyright (c) 1989 American Chemical Society).