text: The paramagnetic ring current resulting from the electron delocalization in antiaromatic compounds can be observed by NMR. This ring current leads to a deshielding (downfield shift) of nuclei inside the ring and a shielding (upfield shift) of nuclei outside the ring. [[Cyclododecahexaene|[12]annulene]] is an antiaromatic hydrocarbon that is large enough to have protons both inside and outside of the ring. The chemical shift for the protons outside its ring is 5.91 ppm and that for the protons inside the ring is 7.86 ppm, compared to the normal range of 4.5-6.5 ppm for nonaromatic alkenes. This effect is of a smaller magnitude than the corresponding shifts in aromatic compounds.
  Many aromatic and antiaromatic compounds (benzene and cyclobutadiene) are too small to have protons inside of the ring, where shielding and deshielding effects can be more diagnostically useful in determining if a compound is aromatic, antiaromatic, or nonaromatic.  Nucleus Independent Chemical Shift (NICS) analysis is a method of computing the ring shielding (or deshielding) at the center of a ring system to predict aromaticity or antiaromaticity. A negative NICS value is indicative of aromaticity and a positive value is indicative of antiaromaticity.