Understanding Aromaticity in [5]Helicene-Bridged Cyclophanes: A Comprehensive Study

Abstract

This study explores the aromaticity of doubly [5]helicene-bridged (1,4)cyclophane and triply [5]helicenebridged (1,3,5)cyclophane via calculations of the magnetic response and of electronic aromaticity indices. The primary objective is to assess the π-electron delocalization to determine whether they sustain global ring currents associated with π aromaticity. The molecules show local ring currents in the presence of an external magnetic field. The ring currents flow diatropically in the stacked six-membered rings and in the helicene arms. However, these π currents are not interconnected due to the discontinuity of the π delocalization at the C−C single bonds connecting the central six-membered rings to the helicene arms. Electronic indices suggest that the helicene-arm systems have significantly smaller electron delocalization than benzene. The reduction in the delocalization does not compromise their ability to exhibit ring currents in the presence of an external magnetic field. The analysis provides further evidence that the magnetic criteria yield a different degree of aromaticity for the helicene arms than obtained in the calculation of the electronic aromaticity indices. However, both approaches confirm that the studied molecules are not globally aromatic.

Multiconfigurational actinide nitrides assisted by double Möbius aromaticity

“…It has been well recognized that the NICS has limitations for assessing aromaticity in heavy metal clusters 84–88 and even in organic molecules. 89 In this regard, the negative NICS values for Ac 2 N 2 may just be a coincidence. In contrast, the global diamagnetic induced ring-current is believed to be a more reliable criterion for aromaticity in heavy metal clusters, 90–93 and has been well-validated in a comprehensive theoretical work by Orozco-Ic et al very recently.…”