Final answer:
The configurational change from all-trans-lycopene to 13-cis-lycopene catalyzed by iodine can be detected by a shift in UV-Vis spectral peaks, as the extended conjugated pi system's HOMO-LUMO gap changes, affecting light absorption.
Step-by-step explanation:
When iodine catalyzes the isomerization of all-trans-lycopene to 13-cis-lycopene, a configurational change occurs. This change can be detected as a shift in the UV-Vis spectral peaks associated with the molecule. Molecules like lycopene with extended conjugated pi systems have narrow HOMO-LUMO energy gaps, which allows them to absorb light in the visible spectrum range.
A change from the all-trans form to the cis form can be indicated by a shift in the wavelength of maximum absorbance (λmax) because the two forms have different energy profiles and interact differently with light. In the case of all-trans-lycopene, the spectral peaks might shift toward a different wavelength as the pi-bond conjugation is affected by the configurational change, altering the molecules' interaction with light and therefore how it absorbs.