Figure 1.

a) Molecular structure of the naphthalene derivative ¹³C₂-I. Black filled circles indicate the ¹³C₂ labeling sites. b) ¹³C spectrum of I in [D₆]acetone solution, acquired at 9.4 T with 512 transients. The two peaks separated by 0.06 ppm indicate the resonances of the inequivalent ¹³C nuclei. c) The ¹³C spectrum of ¹³C₂-I acquired at 9.4 T with a single transient shows a single peak with a full-width-at-half-height of 1.5 Hz.