Final answer:
The compound that absorbs the highest wavelength of UV light among the choices given is 1,4,7-octatriene (c), due to its extended system of conjugated double bonds. Option C is the correct answer.
Step-by-step explanation:
The student asked which compound absorbs a higher wavelength of UV light, given the options of 1,3-butadiene, 1,3,5-hexatriene, 1,4,7-octatriene, and ethene. To answer this, we need to understand that as conjugated pi systems in molecules become larger, the energy gap for a π - * transition becomes increasingly narrow, meaning that the wavelength of light absorbed gets correspondingly longer.
1,3-butadiene, with two conjugated double bonds, absorbs UV light at 217 nm. The rule of thumb is more extensive conjugation, longer wavelength absorption. 1,3,5-hexatriene, which has three conjugated double bonds, shows absorption at a longer wavelength of 258 nm. 1,4,7-octatriene would have an even longer conjugated system compared to 1,3,5-hexatriene, therefore it would absorb light at a wavelength longer than 258 nm. Ethene, with only one double bond, has the shortest wavelength absorption at 165 nm due to a π - * transition.
Therefore, 1,4,7-octatriene absorbs the highest wavelength of UV light compared to the other compounds listed. This is due to its extended system of conjugated double bonds, which lowers the energy gap associated with electronic transitions.
The correct option is c. 1,4,7-octatriene.