The panorama of atomic participation in the eigenvectors presented in Fig. provides very instructive picture of the reaction mechanism. First, it becomes evident that the hydrogen atoms (H5, H6) serve as sensors for the actual changes introduced along the reaction path, even if they do not play directly a role in this process. Drifting H4 away from the N1 nitrogen is dramatically sensed by H5 and H6 atoms; docking H4 at O3 is manifested sharply by the distant H6 atom. Two heavy atoms (N1, C2) do not show dramatic alternation in their involvement in any of the atomic modes, despite the evident changes in their bond structure: