On the aromaticity and stability of benzynes in the ground and lowest-lying triplet excited states

Update for Isomerization Stabilization Energies: The Fulvenization Approach

An alternative approach for calculating aromatic stabilization energies is proposed based on transforming an (anti)aromatic ring into a fulvene isomer. This fulvenization process gives a value of 34.05 kcal·mol-1 for benzene in the singlet state and a value of -17.85 kcal·mol-1 in the triplet state. Additionally, it is possible to use experimental values (as long as they exist) for the calculation as the gas-phase formation enthalpies of benzene and fulvene, whose difference is 33.72 kcal·mol-1. On the other hand, this same approach has been evaluated on several six-membered rings, including those persubstituted, biradicals, azines, and inorganic analogues, giving results in agreement with those reported in the literature using different criteria. Additionally, it is possible to differentiate the aromaticity of the rings in polycyclic aromatic hydrocarbons according to Clar's rules. Assigning the (anti)aromatic character in various nonbenzenoid rings (neutral and charged), except for five- and seven-membered rings, is also possible. The construction of the fulvene isomers in PAHs is set such that nonaromaticity-related effects are not considered. The results show that the fulvenization approach is an effective and efficient approach that can serve as an alternative or complement to existing tools.