A total of 20 specific bonds are changed in the entire reaction dataset although the total number of bonds possible with the combination among the five atoms is larger. The number of changes of each of the 20 specific bonds is depicted in Figure . In a bond between atom X, and Y, single, double, triple, and aromatic bonds are denoted by X s Y, X d Y, X t Y, and X Y A, respectively. For example, there are no bond changes in the reaction dataset involving the F atom. This is because F can only form a single bond, and in an A ↔ B type of reaction, changing the bond of F from one atom type to another did not occur in our reaction dataset. Furthermore, the change in the number of bonds involving non-C atoms is less than the ones involving C.