Quantum molecular similarity. Part 2: The relation between properties in BCP space and bond length

In previous work we introduced an abstract space of bond critical point properties, called BCP space, to measure the similarity between molecules. In this contribution we critically examine the dependence of properties in BCP space on equilibrium bond length, a topic which has been extensively investigated in the literature. For that purpose we have designed a data set of 57 molecules yielding 731 bond critical points. We confirm the existence of local linear relationships provided the bonds vary little in their chemical surroundings. Such relationships break down completely for larger subsets of bond critical points encompassing a wider variety of bonds. The patterns observed in the global picture show so little correlation that one may safely conclude that BCP properties cannot be trivially recovered or even predicted by knowledge of bond length alone.