Aromaticity of N‐heterocyclic carbene and its analogues: Magnetically induced ring current perspective

Abstract

AbstractThe N‐heterocyclic carbene, imidazole‐2‐ylidene, and its main group (13‐15) analogues contain cyclically conjugated 6π electrons. Experimental 1H nuclear magnetic resonance (NMR) spectra suggest an increase in aromaticity along a period from left to right. Whereas the order along a group is as follows: period 2 > period 5 > period 4 > period 3 due to change in structure. To understand the order of aromaticity, the magnetically induced ring currents of the molecules are calculated using aromatic ring current shielding, gauge‐including magnetically induced currents (GIMIC) method and Stanger's σ‐model applying the gauge‐including atomic orbitals NMR technique. It is found that GIMIC best describes the order of aromaticity especially along a group where current‐profile changes on the bivalent atom down a group due to change in electron density. Moreover, the GIMIC provides the visualization of current by sign modulus and the anisotropy of the induced current density plots.