Aromaticity Hidden in Magnetically Antiaromatic Macrocycles
Year: 2026
Type: preprint
Abstract: Global paratropic ring currents give norcorrole and rosarin a familiar antiaromatic label and account for their characteristic pattern of deshielded inner and shielded outer protons. Translating that magnetic picture into a perimeter of alternating double bonds, however, assigns the occupied 𝜋 electrons to a bonding pattern that the current pathway alone does not determine. Here we ask how much of the ground-state bonding the magnetic response actually reveals. For a diaza[16]annulene model series and for free-base and metal-coordinated porphyrinoids, we compare occupied bonding domains, resolved with the electron density of delocalized bonds and the bond delocalization function, with orbital-resolved magnetic response. A global paratropic pathway persists when the model bonding changes from a delocalized 16𝜋 perimeter to localized double bonds or two pyrrolic sextets. In norcorrole and rosarin, fixed sextets give way to migrating patterns upon coordination, again without changing the paratropic classification. Orbital decomposition reveals local diatropic contributions beneath the global response. Isomerizations involving the pyrrolic units of norcorrole cost more than the rim control, although their energies also contain structural and stereochemical effects. A paratropic ring current is therefore not, by itself, a bonding formula. Annulene-based aromaticity assignments should retain Hückel’s energetic logic, with electron counts and magnetic or spectroscopic fingerprints interpreted through the complete molecular electronic structure rather than substituted for appropriate energetic and, where relevant, thermodynamic characterization.
Source: ChemRxiv
Language: English
Subfield: Organic Chemistry
Field: Chemistry
Domain: Physical Sciences
Open Access status: green
OpenAlex ID: W7223171742