Notably, this result for the reaction anharmonicity A  in eq. 31, is entirely localized in bonds/contacts between atoms. The new quantity, / AB AB a dC d =-  , has been introduced in previous works from this laboratory under the name "bond fragility". Relation of the bond fragility to the physical measures of anharmonicity can be demonstrated (eq. 32), with the atomic anharmonicity vectors introduced and discussed in our previous work . The role of DF Connectivity Matrix has been fully exposed, because the variations of its elements described by the bond fragilities AB a  have now been proved to indeed reflect the real chemical changes in a system.