Electronic spectra of large-ring heterocyclic compounds

2 Electronic spectra of large-ring heterocyclic compounds 

Many 1,2-diazocines, including the parent (12) (79JOC1264) and its 3,8-diaryl-4,7-dichloro derivatives, are yellow (85CJC1829). However, the color is quite sensitive to substituents, as replacing one or both chlorines in the 4 and 7 positions by nitrogen or sulfur substituents, leads to colorless compounds (87BCJ731). 

The parent 1,4-dioxocin (15) is colorless, with its major absorption band well into the ultraviolet [238 nm (3.86)] and a weak shoulder at 285 nm (2.50), a spectrum similar to that of 1,3,6-cyclooctatriene (72AG(E)935). 

The ultraviolet spectra of l,5-dithia-2,4,6,8-tetrazocines (16 R=Ph) (klllM 306.5 nm) and (16 R = NMe,) ( mH 229nm) reflect the unusual structural dependence on substitution that exists for these compounds (81JA1540). Whereas the former compound has perfectly planar eight-membered ring, the 3,7-bis(dimethylamino) derivative was folded about an axis drawn through the two sulfur atoms as shown in (17) (see also Sec. 2.5.4.2.2). 

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