Comment on 'Origin of the Nonplanarity of Tetrafluoro Cyclobutadiene,C4F4'

摘要

In a recent paper,Seal and Chakrabarti claim that the origin of the nonplanarity of tetrafluoro cyclobutadiene (1) is aroma-ticity and a second-order Jahn-Teller effect.The claims for aromaticity rest on NICS(O) and NICS(1)_(zz) values.However,it had been shown that a single NICS value may fail in assigning aromaticity,and the NICS-scan method was introduced.This was demonstrated specifically for derivatives of cyclopentadiene that were erroneously characterized as being aromatic or antiaromatic on the basis of single NICS values.4 These investigations further revealed that simple NICS parameters may indicate diatropic and paratropic ring currents,but they do not necessarily signalize aromaticity or antiaroma-ticity,as evidently there are systems that show diatropic ring currents but are not aromatic.