[18]-Annulene exhibits a 1H NMR spectrum that is unusual in that in addition to a peak at ? 8.8 ppm, it contains a second peak having a chemical shift ? of - 1.9 ppm. A negative value for the chemical shift ? indicates that the protons are more shielded than those of tetramethylsilane. This peak is 1.9 ppm upfield from the TMS peak. The high-field peak has half the area of the lowfield peak. Suggest an explanation for these observations.

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[18]-Annulene