[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 δ of -1.9 ppm. A negative value for the chemical shift δ indicates that the protons are more shielded than those of tetramethylsilane.
This peak is 1.9 ppm up field from the TMS peak. The high-field peak has half the area of the low field peak. Suggest an explanation for these observations.

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[181-Annulende