ABSTRACT. The theoretic foundations of the novel method for the comprehensive studies on the mechanism of the evolution of the electronic structure in a chemical reaction have been presented. Our method provides quantification for both the sequence of bond forming and breaking and the degree of bond (order) modifications along the chemical reaction path. The new Density Functional Connectivity Matrix has been introduced: its elements are the divergences of the Hellmann-Feynman forces for atoms in a molecule over the atomic displacements. They have been proved to describe to what extend atoms in a molecule are actually connected with chemical bonds or bonding interactions. The matrix provided foundation for the Reaction Fragility Method.