An anticipated, indirect relation between anharmonicity phenomenon and a chemical reaction has also been present in the unified reaction valley approach (URVA) by Kraka and collaborators. Their description of the chemical reaction mechanism is derived from the evolution of the normal modes (independent oscillators) along the IRC reaction path by the transformation to the diagonal force constant matrix K . Introduction of the adiabatic curvature coefficients tentatively assigned to bonds, as developed by these authors, allows for replacing the need of discussion of anharmonicity. Each step along the reaction path is described by the set of harmonic oscillators with different force constant at each step. One distinguished mode follows the reaction path (at 𝜉 = 0 it is a transition state mode), the rest 3N-7 modes are perpendicular to the reaction path and to each other. These normal modes undergo variation along the IRC path; the nonadiabatic curvature coefficients provide information on which mode drives the reaction and the Coriolis coefficients show which modes tend to exchange energy with each other. The authors have presented an ingenious approach to localization of the normal modes into a predefined molecular fragment: "the fragment motion is considered as a motion being obtained after relaxing all parts of the vibrating molecule but the fragment under consideration." The term local modes has been adopted for these adiabatic internal coordinate modes. The proof has been presented that the local stretching force constant for an AB entity reflects the intrinsic strength of the bond/interaction between atoms A and B. The local stretching force constants have been claimed to represent the "universal measure of the intrinsic strength of a chemical bond based on vibrational spectroscopy The important practical advantage of the Reaction Fragility method rests on simplicity of its numerical procedure: computation of the full Hessian matrix is the condition both necessary and sufficient for its implementation. Whenever a procedure exists for obtaining branches of the IRC path, then also the Hessian for each branch will be obtained straightforwardly, and the Reaction Fragility monitoring is possible for each branch of the bifurcation. The Reaction Fragility method also is not vulnerable to the trajectories of the second order transition states with two negative frequencies. For the Reaction Fragility method the reaction path is just a trajectory connecting points of variable molecular geometry and yet, the principal advantage of the method comes from the fact that it is exact.