Abstract: Recently, many scientists have been making appointments to encapsulate atom(s) or molecule(s) inside fullerenes. We calculated the structure and electronic properties of the endohedrally acetylene, ethylene and ethane doped(5,5) armchair single-walled carbon nanotube(SWNT) theoretically using B3LYP level of Density Functional Theory(DFT) on 6-31G(d) basis sets. The calculation results suggest that the formations of C₂H₂@(5,5)SWNT, C₂H₄@(5,5)SWNT and C₂H₆@(5,5)SWNT are endothermic; the frontier molecular orbital analysis shows that doping of hydrocarbon molecule made the increment of the HOMO-LUMO gap; the insertion of the hydrocarbon molecule in the center of the nanotube enlarge the diameter of the nanotube and the nanotube outside made the C—C and C—H bond lengths of hydrocarbon molecule compressed slightly and the bigger the dopant is, the tighter the compression is; a small quantity of electron transfer happens from(5,5) SWNT to the hydrocarbon molecule and the amount of the electron transfer in the three compounds is in the following sequence of C₂H₂@(5,5) SWNT<C₂H₄@(5,5) SWNT<C₂H₆@(5,5) SWNT.

Key words: Armchair single-walled carbon nanotube, Acetylene(ethylene, ethane), Charge transfer, Binding energy, Deusity Functional Theory