ABSTRACT Carbon nanotubes are either single-walled (SWCNTs) or multiwalled, and the former attract more attention due to their unique electronic, optical, and spectroscopic properties. One of the main recognized structures of carbon nanotubes is the (5,5) armchair single-walled carbon nanotube. Endohedral metalofullerenes of the form M@C x were introduced as an important class of spherical fullerene group with unique properties. Formation of endohedral metallofullerenes is thought to involve the transfer of electrons from the encapsulated metal atom(s) to the surrounding fullerene cage. Two of these molecules are La@C82 (a) and Y@C82(b). To establish a good understand of structural relationship between the structures of the molecules La@C82, Y@C82, and SWCNT(5,5)-armchair-CnH20 (n = 20–190) (1–18), the number of carbon atoms (n) of the SWCNTs was used as one of the useful numerical and structural electrochemical properties of the unsaturated compounds. The relationships between this index and the first an...