3 Existence of the polycations of linear and cyclic conjugated hydrocarbons In the following, we will treat the dissociation of the two classes of hydrocarbons with extended π-systems as examples: linear polyenes (C 2n H 2n+2 ) and monocyclic Hückel annulenes (C 4n+2 H 4n+2 ), see Figure . We will consider the molecules up to 22 carbon atoms, comprising 11 linear polyenes (n = 1, . . . , 11) and 5 annulenes (n = 1, . . . , 5). For the polyenes, the all-trans conformations were taken. The computational results (structures and energies) can be found in the SI.