All five of these structures are non-classical in the sense that their structures do not conform to the standard bonding concepts observed for the overwhelming majority of organic compounds. The evidence from theory and experiment, suggests that structures I, II, and III are the most likely to be the stable structures. All have a positive charge. Debate still exists as to what is actually being observed. The top number is the bond order, and the bottom number, in parentheses, is the bond length in Angstroms.
All structures have a positive charge.
These are shown in Fig. Clearly, there is not always a bond when the CC distances are close. This compares reasonably well with our calculated value. VI was calculated. The top number is the bond order, and the bottom number, in parentheses, is the bond length in Angstroms.