<i>Per</i>iodoannulenes: A Generalized Annulene-within-an-Annulene Paradigm for Combined ? and ? Ring Currents

Periodoannulene molecules and ions CxIxq in planar geometry offer examples of systems with the potential for outer ? inner ? ring-current double aromaticity, given a sufficient overlap tangential p?-orbital manifolds on large atoms cycle. Previous theoretical work indicated concentric diatropic currents dication C6I62+. Ab initio ipsocentric calculations support an account terms frontier-orbital selection rules current contributions C6I62+ (and radical C6I6+, implicated recent experimental oxidation periodobenzene). A ?/? analogue annulene-within-an-annulene model is applied here to periodo based cyclooctatetraene. Model species C8I8q charges q = 0, +1, +2, +4, -2 structures constrained D4h symmetry exhibit maps all combinations con- counter-rotation, comprising global ring iodine perimeter central carbocycle. All can be rationalized by separate application tropicity two subsystems, whether singlet or triplet states.