Two quantitative characterizations are compared for series, each of which consists of a central atom or molecule and successively attached functional groups. The vector index component V2 brings out the periodicity related to the central entity and to the ligands (if they are atoms) or brings out the periodicity related to the substituents (if they are atoms) put into an originating molecule. The Zenkevich parameters also show the periodicity seen in V2 but are valuable for treating data farther from linearity with respect to the number of attached groups provided that there is not an inflection point. An algebraic comparison shows that it is not possible to derive the vector index components from the Zenkevich parameters or visa versa except when the data are exactly linear.
Hefferlin, Ray, "Two Descriptors for Series of Congeneric Molecules" (2008). Faculty Works. 9.