where 𝜃 𝑖 and 𝜃 𝑖 0 are the bond angles in the cyclic and strain-free species, respectively, and 𝑘 𝑖 𝜃 is the force constant associated with the bond angle . Alternatively, RSE can also be calculated as the energy difference in a homodesmotic reaction where one side of the reaction includes the ring structure, and the other side contains a reference counterpart . This homodesmotic reaction is usually balanced using simple molecules like methyl groups or ethane to ensure that the number of atoms and bond types are equivalent on both sides . In either case, it is necessary to find the optimal 3D structure, compute the energies, and then determine the RSE as the energy difference .