The essential reasons for the differences in aromaticity of the three isoelectronic species deserve to be explored in depth. In order to investigate the utility of C atom in changing the aromaticity of the isoelectronic analogues of benzene, we analyzed the pre-natural atomic orbitals (PNAOs) of atoms of the three molecular rings, as shown in Figure . The degree of overlap of the PNAOs is closely related to strength of  interactions. One can see that the order of spatial extent of the 2pz atomic orbitals of the B, C, and N atoms is in the order of B atom > C atom > N atom. In other words, introducing the C atom is equivalent to building a bridge between the B and N atoms that promotes -electron delocalization, which greatly weakens the serious hinderance to electron conjugation caused by the huge electronegativity difference between the two elements. Similar conclusion has been obtained in the exploration of the aromaticity of isoelectronic species in C18. Atom color code: white, H; red, B; grey, C; blue, N.