where Ropt is the optimal bond length for a reference aromatic bond, n the total number of bonds within the ring, and ⍺ serves as a normalization factor 60 to scale the result to a value between 1 and 0, where 1 indicates perfectly aromatic benzene and 0 represents the hypothetical Kekulé structure of a nonaromatic 1,3,5-cyclohexatriene ring. The Ropt and ⍺ values for CC, CN, CO, CS, NN, and NO bonds were taken from the literature. For the NS bond, the optimal bond length Ropt = 1.61 Å was also taken from the literature, 61 whereas the 𝛼 (71.875 Å -2 ) was calculated according to standard procedures. 58