Absorbance maxima of polyenes [closed]








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Can anyone tell me how to approach this question from USNCO 2013? 




The question boils down to: which molecule has the longest conjugated $\pi$-system? The answer is (A). For such a system, the particle-in-a-box model is a decent approximation and one can show that larger systems absorb at lower energies, i.e. longer wave-lengths.


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