In spiropentadiene the same clear trend emerges. We plot the torsion profile starting from the constrained C 2v and fully optimized D 2 minima in Figure . at 90 • , bond-length distortion splits SOMO and HOMO by around 1 eV (red), while they are near-degenerate in the D 2 structure (blue). In both cases torsion stabilizes the doubly-occupied HOMO and destabilizes the SOMO. This again correlates with torsion (de)stabilizing the MOs depending on their helicity (ESI Figure ). The frontier MO eigenvalues drive torsion towards a minimum at around 60 • . Like in the allene case, this minimum is higher in energy when there is bond-length alternation and the helical frontier MOs are thus stabilized by equal π-bond lengths. The frontier MO energies correlate closely with the total energy (Figure dichloroallene and 1,4-dichlorospiropentadiene have helical MOs in both neutral and cationic species due to their lower symmetry. Given the helical MOs seem to be a controlling factor in the structure of allene and spiropentadiene radical cations, we are encouraged to analyze if the helical topology of the π-MOs manifests itself in terms of electron delocalization. There is limited experimental work suggesting such delocalization in ionic species, which is somewhat in support of this hypothesis. To provide a qualitative measure, we assess topology of the electron density using LOL in order to visualize the delocalization patterns.