Electronic spectra of small-ring heterocyclic compounds

1 Electronic spectra of small-ring heterocyclic compounds 

Saturated three- and four-membered heterocyclics absorb little in the readily accessible regions of the UV spectrum. Sulfur-containing rings are an exception, as can be seen in Table 9, Despite the lack of absorption of most parent compounds, there is a wealth of photochemistry of small heterocyclics. Light absorption by substituents, and energy transfer from photoexcited molecules present in the photoreactive system make photoconversion of the heterocycles practical. On the other hand, the lack of substantial absorption of their own can be exploited in the preparation of small heterocycles, by designing the system to be unsuitable for destructive energy transfer. 

The introduction of a second heteroatom (other than sulfur) does not drastically change the absorption characteristics of small heterocycles. Oxaziridine and diaziridine are still transparent to light of wavelengths above 220 nm (CHEC 5.08.2.3.2). 

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