Aromaticity of charged cyclocarbon radicals (Cn± = 6–30)

Abstract

Aromaticity of charged cyclocarbon radicals (С_n^±=6–30) have been studied computationally at density functional level of theory based on the magnetically induced ring-current calculations. It was found that the M06-2X functional correctly reproduces the radical structure of charged cyclocarbons, while the BHandHLYP and wB97XD functionals tend to have spin contamination problems. Charged cyclocarbon (n = 6–20) radicals have a pronounced difference in the BLA between n = 4k/n = 4k +2 structures. Charged cyclocarbons (n = 6–22) are characterized by an alternating aromaticity satisfying the n = 4k/4k +2 rule. This rule breaks down in predicting the aromaticity of cyclocarbons with n ≥ 24, where the difference in the BLA between n = 4 k/4k + 2 structures disappears.