CHEMICAL-SHIFTS OF THE [N]PHENYLENES AND RELATED-COMPOUNDS

Proton chemical shifts and nucleus-independent chemical shifts (NICS) have been computed for [N]phenylenes and related compounds using the G IAO/HF method. Proton chemical shifts calculated in the 6-31G basis a gree with measured values, where available, within similar to 0.3 ppm. NICS values were calculated at the HF/3-21G level using B3LYP/6-31G geometries. Both proton chemical shifts and NICS values show attenuati on of aromatic and antiaromatic character in the six- and four-membere d rings, respectively, in a manner dependent upon the positions of the se rings in the molecule. These effects are greater in angular than in linear phenylenes. The central ring of a branched phenylene is found to be only slightly aromatic. The protons of the cyclic phenylenes res onate at slightly higher field than their angular counterparts. Both N ICS and proton shifts of antikekulene suggest only slight additional a ntiaromatic character.