As a further argument, it is tempting to consider I4 2-also as a resonance hybrid between [I3 -•I -] and [I -•I3 -] situations (in agreement with the fact that ERMB cannot extend beyond 3 centers). In such a resonance hybrid, the 2-3 bond remains short in both limit formulas, and the 1-2 and 3-4 bonds must be longer, as experimentally observed.