In either case, these represent a departure from a stereotropic process -nuclear fusion in the former case, or formation of a different constitutional isomer in the latter. Our worked example of the chiral silane demonstrated that changes in atom connectivity are idiosyncratic for the atoms involved. In general, there are four possible cases with these shown in Fig. . If both "fusing" B-atoms are chemically identical, a B2 unit will dissociate orthogonally at infinite distance (Fig. ). When the "fusing" B-atoms are distinct, a B2 unit can either dissociate collinearly at infinite distance (Fig. , Case B), one B-atom may remain bonded to the A-atom while the other dissociates to infinite distance (Fig. , Case C), or one B-atom may remain bonded to the A-atom while a B-B bond forms and a sequentially bonded linear A-B-B geometry results (Fig. ).