ABSTRACT Cyclo n carbons, pure carbon rings with two orthogonal π systems (in‐plane and out‐of‐plane), have recently become experimentally accessible, offering a rare opportunity to investigate double‐π aromaticity. We conduct a systematic DFT study on cyclo n carbons ( n = 6–26), using structural, delocalization, and magnetic‐response descriptors to establish a consistent aromaticity map. A clear odd‐even oscillation and size dependence emerge: rings with (4 n + 2) π electrons in both manifolds ( n = 6, 10, 14, 18, 26) show strong double‐π aromaticity, while 4n systems ( n = 12, 16, 20) exhibit pronounced antiaromaticity. Cyclo13carbon lies near the aromatic–antiaromatic crossover. These behaviors originate from size‐dependent bond‐length alternation and π‐delocalization pathways, which determine the strength and direction of induced ring currents and associated shielding effects. Our results provide a unified framework for understanding double‐π (anti)aromaticity in carbon nanorings and offer practical guidance for interpreting experiments and tuning their electronic properties via ring size or electron count.
Sun et al. (Sun,) studied this question.