Magnetic Anisotropic Effects in Charged Aza[10]annulene Analogs with a Non‐planar Carbon Framework

Abstract

Classically, aromaticity portrays the unique stability and peculiar reactivities of cyclic planar conjugated systems with (4n+2) π electrons. Understanding the electronic environments in new chemical frameworks through experimental and theoretical validation is central to this ever‐expanding theme in chemical science. Such investigations in curved π‐surfaces have special significance as they can unravel the variations when the planarity requirement is slightly lifted. In this report, we discuss the synthesis, spectroscopic and theoretical studies involving a new group of cyclazine analogs having a charged aza[10]annulene periphery, centrally locked through a sp3 carbon. Magnetic anisotropic effects arising from electron delocalization through its curved π‐surface were mapped through a specific set of chemical groups introduced through this sp3 carbon. The nucleus‐independent chemical shift calculations revealed negative chemical shift values, indicating the aromatic nature of the aza[10] annulene rim. This is corroborated by a clockwise diatropic ring current, evident from anisotropy‐induced current density analysis. Variations in the chemical shift of NMR signals in these systems were also computationally examined through isotropic chemical shielding surface analysis.