Chiroptical structure-property relations in cyclo[18]carbon and its in silico hydrogenation products

The anisotropy of the optical activity of cyclo[18]carbon (C₁₈), fully hydrogenated C₁₈ (C₁₈H₃₆), and 26 hydrogenated compounds of intermediate composition, C₁₈H_2n, n = 1,2…17, were computed. These compounds were selected because they resemble loops of wire. The maximum gyration for acetylenic and cumulenic subgroups of compounds was linearly proportional to the product of the geometric area over which the charge can circulate, multiplied by the largest separation between carbon atoms on opposing sides of the loops. These geometric quantities can be likened to transition magnetic dipole moments and transition electric dipole moments, respectively, that can be generated in electronic excitations and which contribute in the main to nonresonant optical activity. The correlation between a computed geometric product of distance and area, and a quantum chemical property, establishes that chiroptical structure-activity relationships can be well established for judiciously chosen series of comparatively large compounds.