1,3-disubstituted allenes behave similarly to allene. The radical cation of 1,3-dicholoroallene relaxes by torsion into a structure where the equal bond lengths are retained. In a constrained optimization where the 90 • dihedral angle is fixed, the molecule relaxes into a higher energy structure with bond-length alternation (Figure ). However, the 1,1-dichloroallene radical cation is different, and bond-length distortion is preferred over torsion. The cation retains the C 2v symmetry of the neutral molecule when optimized. If the bond lengths are constrained to equal lengths, the cation relaxes with torsion into a higher energy structure (Figure ). These two substituted allenes each prefer one of the two possible relaxation routes of the parent allene. We therefore examine them as model systems for the JT distortion in allene. Both neutral and cationic 1,1-dichloroallene are C 2v symmetry structures, therefore their frontier MOs are rectilinear π-MOs. The two double bonds have different lengths due to the polar nature of the substituents. Shown in Figure , the HOMO and SOMO are split by around 1 eV at 90 • torsion due to the bondlength alternation. We compare the torsion profile of the eigenvalues and the total energy in Figure and. Torsion only marginally stabilizes the doubly-occupied HOMO eigenvalue of the cation. Consequently, torsion is not energetically favorable for the total energy nor the combined frontier MO energies as plotted in Figure .