The structural adjustment from neutral to radical cation in allene and spiropentadiene (Figure ) are part of a series of systematic changes from the neutral into the dicationic species. Let us start by examining an intuitive description of the structures of linear molecules. In allene, the two double bonds are traditionally assigned into each of its planes to account for its perpendicular end-groups. Alternatively, a coarctate orbital system can be assigned as defined by Herges. We make this model of linear molecules starting from the Möbius-Hückel concept by Zimmerman. This complementary description assumes extensive delocalization in linear molecules, but does not contest the logic offered by traditional bonding and orbital models.