The MOs of C 18 -(CO) n can be considered as the result of mixing the MOs of the -CO and C 18 -fragments. The analysis of the interaction between the fragment MOs in As shown in the previous IRI- analysis and the subsequent electron delocalization analyses, after the combination of (CO) 2 and C 18 , the  in electron conjugation is destroyed around the junction region between the two fragments. Two underlying reasons are: (1) the introduction of the -CO groups causes obvious distortion on the C 18 structure, especially makes severe in-plane bending of the C-C-C angles in the carbon ring near the -CO groups, which leads to evident difficulty in  in electron conjugation over this region; (2) as can be seen in Fig. , the MOs of -(CO) 2 and the  in orbitals of C 18 -produce a significant mixing, resulting in new occupied MOs of C 18 -(CO) 2 clearly display the character of  bonds between the -(CO) 2 and C 18 -moieties. Since  electrons are well known to be strongly localized, the originally globally delocalized  in electrons in C 18 can no longer delocalize over the bonds where carbon ring binds to the two -CO groups.