Calculated dissociation energies and molecular bending barriers of tetracene (C₁₈ H₁₂), pentacene (C₂₂H₁₄), hexacene (C₂₆H₁₆), and heptacene (C₃₀H₁₈). The dissociation energy for removing a terminal side hydrogen atom from these molecules is about 4.8 eV. The molecular bending barrier decreases from ~6.7 to ~4.2 eV as the length of the molecule increases. Following the transition states (shown in red), closed hollow carbon structures can be formed. The blue circles highlight the region where the reactions take place.