The HOMO-LUMO gap in alkenes H-(HC=CH)n-H decreases as n increases. Hence, there is a red-shift in the absorption of the polyenes. Ethene, butadiene, hexatriene and octatetraene absorb at 165, 217, 256 and 290 nm. Find the eigenvalues of the HOMO and of the LUMO of ethene, butadiene, hexatriene and octatetraene and compare the HOMO-LUMO gaps.