Evolution of the atomic valence observed by the reaction fragility spectra on the reaction path

The computational fragility spectra of atoms on the reaction path are presented for a selection of canonical processes represented by an amino group rotation around the (X)HC-NH(Y) bond (X = O, S; Y=H, CH₃). Calculated spectra are found to very accurately describe the variation of atomic valence. Significant linear correlation is also demonstrated between the Wiberg bond indices and the corresponding elements of the connectivity matrix, instrumental for calculation of the spectra. Demonstrated atomic fragility spectra contain rich and subtle information on the variation of the bonding status of all atoms, including the weak interacting individual hydrogens. Correlation with the atomic valences confirm the earlier finding that the spectra contain a picture of the electron density flow upon a reaction.