An ab initio study of the NMR properties (absolute shieldings and NICS) of a series of significant aromatic and antiaromatic compounds

The absolute shieldings of protons and the nuclear independent chemical shifts of six aromatic and antiaromatic hydrocarbons have been calculated at the GIAO/B3LYP/6-31G∗ level. In general, the results are in agreement with the experiment ones except in the case of 1,5,9-tridehydro[12]annulene 7. Three possible explanations have been tested for this compound concluding that the anomaly (∼14 ppm!) probably lies on the use of a DFT approach.