The Cartesian coordinates of the ground-state H-C18-H, H-C18-NO2, NH2-C18-H, and NH2-C18-NO2 are given in Tables , respectively, and their selected characteristic parameters are listed in Table . There is no imaginary frequency in all vibrational frequencies of the C18 derivatives studied, confirming that the optimized geometries are local minima on their respective potential energy surfaces (PESs). The average atomization energies (Ea) of the molecules were calculated to be 6.84 to 7.59 eV, which are large values indicating their high stability. similar long and short axes in length (d1 and d2), and their ovality factors (e) of C18 unit are distributed in a small range of 1.64-1.69. All C18 derivatives are C2v symmetric planar molecules. The line connecting the two functional groups of H-C18-NO2, NH2-C18-H, and NH2-C18-NO2, namely the molecular long axis, is their principal axis, while the principal axis of H-C18-H is its short axis, which means that the two carbon-chain bridges in the first three molecules are identical, while the bridges in the last one is not. We present the bond-length colored molecular structure of the derivatives in Figure , from which it can be observed that the carbon-atom skeleton of the derivatives, like the free C18, all still show a polyynic structure with alternating long and short C-C bonds.