The bond order (BO) is an important concept in chemical bonds analysis, which can quantify multiplicity or strength of bonds. Mayer, fuzzy, and Laplacian BOs of C 18 Br 6 were calculated and shown in Figure , together with corresponding bond lengths. There is a good correlation between the bond length and BOs of the molecule and the results of various BO analyses describing the bonding characters are consistent quantitatively. The C 18 Br 6 is shown to be a polyynic structure with alternating long and short C-C bonds like C 18 ring. Since its BOs of long and short bonds deviate significantly from the integer values of 1 and 3, respectively, the long and short bonds cannot simply be regarded as ideal single and triple bonds, which precisely indicates the existence of electron delocalization over C-C bonds in the molecule.