Experimentally, RSE can be determined from the difference in the heat of formation between the cyclic molecule and an appropriately chosen strain-free counterpart. Although the heat of formation of common molecules can be estimated using the additivity rules with a group equivalent scheme, experiments are necessary for complex molecules . Theoretical estimation of RSE can be achieved via ring bond angles and ring bending force constants, i.e., 𝑅𝑆𝐸 = ∑ 𝑘 𝑖 𝜃 (𝜃 𝑖 -𝜃 𝑖 0 )