NICS-XY-Scan Predictions of Local, Semi-Global, and Global Ring Currents in Annulated Pentalene and s-Indacene Cores Compared to First-Principles Current Density Maps.

Abstract

The magnetic response of a set of 20 molecules, their dications and their dianions has been studied by the NICS-XY method, and the results have been compared with first principles current density maps. The molecules have been built from pentalene and s-indacene by single and double annulation of cyclobutadiene, benzene and benzocyclobutadiene in an alternate fashion on both sides of the molecules. The prediction of tropicities obtained by the NICS-XY method are overall consistent with the current density maps. A literal code, developed to give a compact description of the tropicities of currents flowing around rings and bonds cut by the scan trajectory shows that, in most cases, the NICS-XY method leads to an exact match with the current density analyses. Mismatches are generally due to small circulations out of the scan trajectory, and they do not correspond to misinterpretations of the overall tropicities. The dataset provides several cases where the prediction of the overall antiaromatic/aromatic response by the 4n/4n+2 count of π electrons fails.