Electronic Structure and Aromaticity of an Unusual Cyclo[18]carbon Precursor, C18Br6

Herein, the electronic structure and bonding character of the stable cyclo[18]carbon (C-18) precursor, C18Br6, 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 pi-electrons (labeled as pi(out)- and pi(in)-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(ind)), iso-chemical shielding surface (ICSS), anisotropy of the induced current density (AICD), and the induced magnetic field (B-ind). All these analyses indicate that C18Br6 is a globally aromatic species with lower aromaticity than C-18, and the blocking of in-plane pi-conjugation (labeled as pi(in)-conjugation) by the presence of -Br substituents in it is the underlying cause for the weakening of molecular aromaticity.

Automated summary

In this study, the electronic structure and bonding characteristics of C18Br6, a stable precursor of cyclo[18]carbon (C-18), were characterized using MO, DOS, BO, and IRI analyses. The delocalization of pi(out)- and pi(in)-electrons in bonding regions was examined using LOL and ELF. The aromaticity was investigated through magnetic response analysis, which demonstrated that C18Br6 has lower aromaticity than C-18 due to the blocking of pi(in)-conjugation by the -Br substituents.