The electronic structure of phenylalanine

Just as the particle in a box gives us some imderstanding of the distribution and energies of n electrons in linear conjugated systems, the particle on a ring is a useful model for the distribution of k electrons around a cyclic conjugated system. 

This energy separation corresponds to an absorption frequency of 1409 THz and a wavelength of 213 nm the experimental value for a transition of this kind is 260 nm. 

Even though the model is primitive, it gives insight into the origin of the quantized 7i-electron energy levels in cyclic conjugated systems, such as the aromatic side chains of phenylalanine, tryptophan, and tyrosine, the purine and pyrimidine bases in nucleic acids, the heme group, and the chlorophylls. 

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