The electron counting mnemonic we showed in the first part of the results section assumes complete electron delocalization, which is not justified in the neutral molecules. In the cations, the π-conjugation is inferred by the helical frontier MOs. Rather than be localized on a single linear double bond in allene and spiropentadiene, the helical MOs span the entire length of the molecule. The additional helical delocalization mediated by these frontier orbitals appear to be the controlling factor responsible for the JT distortion in allene and spiropentadiene radical cations.