Adjacent-DIM-Isoelectronic Molecules and Chemical Similarity II

In a previous paper (I ) i t was shown that same-period acyclic triatomic molecules which have equal C1+2C2+C3 g(C), where Ci is the number of valence electrons of atom i and where i = 2 is the middle atom, are at least as similar as isoelectronic molecules and are vastly more similar than are molecules chosen at random. In the present paper, g(C) is defined for three tetra-atomic molecular structures, and it is shown that molecules having the same structure and equal g(C) are at least as similar as isoelectronic molecules and are more similar than randomly chosen molecules. These adjacent Diatomics-in-molecules series thus join isoelectronic molecules and isovalent molecules as tools to determine chemical similarity. It is suggested again that a theoretical basis for the phenomenon might be constructed using a DIM or similar theory in which non-existent bonds are not replaced with diatomic molecules.