1,3-dichloroallene has C 2 symmetry and consequently it has helical frontier MOs. A helical orbital is (de)stabilized by torsion as it becomes more bonding if the helix is unwinding or less bonding if the helix is overwinding. This happens when the optimized cation is subjected to axial torsion in Figure . Starting from 90 • , torsion destabilizes the SOMO and stabilizes the doubly-occupied HOMO as shown in Figure . This change of the eigenvalues reduces the total energy until a minimum is reached at 122 • . The close relation between the change of the combined frontier MO energies and the total energy in Figure validates the naive picture of the frontier MOs as the driving force for the relaxation of the cation. Consequently, removing an electron from the linear π-MO of 1,1-dichloroallene gives pseudo-JT distortion of the bond lengths. On the contrary, removing an electron from the helical π-MO of 1,3-dichloroallene results in pseudo-JT distortion by torsion.