At most pH values, the C spectra display a triplet fine structure due to secondary isotope shifts induced by the randomly distributed O nuclei (see figure ). A representative C equilibrium spectrum of O-enriched 1,2-13 C 2 squarate at 16.5 T and pH = 14.0 is shown in figure . The spectrum displays three sharp peaks. The two outer peaks are separated by ≃ -15.0 ppb and ≃ +15.0 ppb from the central peak. The integrated intensities of the three peaks are in the approximate ratios of 1.2 : 2.0 : 1.0.