of the unmodified molecule and the one exhibiting the (5, 7)–member ring defect. Coronene and pyrene are amongst the smallest PAHs which may exhibit such ring defects. This implies that the internal heat quantity taken by other parts after a hit is the smallest in these molecules, and therefore the probability of reaching the energy of the barrier is high. In this study we represented the boundaries in terms of the size of the PAHs. The minimal energy pathways between the ground and (5, 7)–member ring defected states exhibit minimum activation barriers of 8.21 eV for pyrene and 8.41 eV for coronene for the transformation. The corresponding reverse barriers are 5.92 eV for pyrene and 6.10 eV for coronene, which agrees well with the results of Yu et al. [@yu]. The size of the PAH molecule seems to have no influence on the energy required to build (5, 7)-ring defects. Whereas pyrene retains some of its symmetry due to the symmetry exhibited by the Stone-Wales defect itself, coronene loses much more of its symmetry. The formation of these (5, 7)-ring defects in PAHs may be well supported in AGB stars or PNe. Those environments strongly enable the transition from the 