Features of UV spectra

The spectra of saturated heterocycles show amine n— j absorptions and transitions associated with sulfur. Saturated ethers are usually transparent down to 210 nm. 

The effects of substituents on UV spectral maxima are illustrated in Table 19. The effects are greatest when conjugation is significantly increased, e.g. for strong electron donor substituents in the pyridinium cation. 

The non-aromatic but fully conjugated 1,4-dioxin and its sulfur analogues show absorption at quite long wavelengths. 

Structure of Six-membered Rings Table 18 UV Spectral Maxima (nm) for Benzazines [XmaI (log e)] 

Substituents Position Pyridine (neutral) Pyridine (cation) Pyridine 1-oxide Pyridazine Pyrimidine Pyrazine 

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