Graphical understanding of electron delocalization and aromatic characteristic of unusual cyclo[18]carbon precursor, C18Br6

The stable precursor C18Br6 is of more practical significance than the refreshing but elusive cyclo[18]carbon (C18) at present, and molecular aromaticity caused by π-electron delocalization is an important issue of interest for this unusual molecule. In this paper, the electronic structure and bonding character of the 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 π-electrons (πout- and πin-electrons) in bonding regions are examined using localized orbital locator (LOL) and electron localization function (ELF). The response properties of the molecule to external magnetic field including induced ring current and magnetic shielding characteristic are carefully explored with the anisotropy of current-induced density (ACID), iso-chemical shielding surface (ICSS), and gauge-including magnetically induced current (GIMIC). All these analyses showed graphically that the C18Br6 is less aromatic than C18 and the blocking of πin-conjugation system by the presence of -Br substituents is the underlying cause for the weakening of molecular aromaticity.