The molecular mechanism for the NH3 + LiH -> LiNH2 + H-2 reaction has been elucidated by the combined use of quantum theory of atoms in molecules (QTAIM) and noncovalent interactions (NCI) index. The topology of the electron density, obtained by QTAIM/NCI, is able to identify the evolution of strong and weak interactions, recovering the bonding patterns along the reaction pathway. Thus, the combination of these two techniques is a useful and powerful tool in the study of chemical events, providing new strategies to understand and visualize the molecular mechanisms of chemical rearrangements. Also, for the first time, the topology of the reduced density gradient has been analyzed, taking into account saddle points for the construction of bifurcation trees. This approach has demonstrated the ability of NCI to account for delocalized interactions, very often characteristic of transitions states.