NICS values scan in three-dimensional space of the hoop-shaped π-conjugated molecules [6]8cyclacene and [16]trannulene

Abstract

Usually, the NICS values at 1.0 Å above the center serve as the NICS probe to estimate the aromaticity of planar or nearly planar π-conjugated molecules. How does one judge the aromaticity of hoop-shaped π-conjugated molecules? In this work, [6]₈cyclacene and [16]trannulene are used as representative molecules to further study the aromaticity from a new research perspective by using the NICS values scan in three-dimensional space methodology. A huge difference of aromaticity has been observed in three-dimensional space through the method. The main ring current of [6]₈cyclacene has been located on the stacked [16]trannulene, the distance of which is 0.8 Å to the edge. The main ring current of [16]trannulene has been located on the center cross-section, the distance of which is 1.4 Å to the edge. This demonstrates that the detailed NICS values scan method is more reasonable to describe the aromaticity than a single NICS value. The method is not only helpful in understanding the internal magnetic field structure of hoop-shaped π-conjugated molecules but also of other planar or spherical aromatic structures. In addition to this, the methodology successfully helps us to clearly understand the aromaticity of any point in three-dimensional space and confirm the main ring current position inside a molecule.