Electronic Structure and Aromaticity of an Unusual Cyclo[18]carbon Precursor, C Br.

Herein, the electronic structure and bonding character of the stable cyclo[18]carbon (C ) precursor, C Br , are thoroughly characterized by molecular orbital (MO), density of states (DOS), bond order (BO), and interaction region indicator (IRI) analyses. The delocalization characters of out-of-plane and in-plane π-electrons (labeled as π - and π -electrons, respectively) in bonding regions were examined using localized orbital locator (LOL) and electron localization function (ELF). The aromaticity was investigated, studying the molecular magnetic response to external magnetic field by computing the magnetically induced current density (J ), iso-chemical shielding surface (ICSS), anisotropy of the induced current density (AICD), and the induced magnetic field (B ). All these analyses indicate that C Br is a globally aromatic species with lower aromaticity than C , and the blocking of in-plane π-conjugation (labeled as π -conjugation) by the presence of -Br substituents in it is the underlying cause for the weakening of molecular aromaticity.