please help wirh explaining this!!

In the IR spectra of the molecules below, the C=C signals do not appear at the same wavenunber. The C=C for the molecule on the left is shifted to a lower cm (moved to the right in the spectrum by 8 cm *), relative to the molecule on the left. Explain. For this molecule, the C=C appears at a lower wavenumber (is shifted 8 cm 1 to the right in the spectrum)