Heterocycles saturated, sulfur containing

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. 

Saturated three- and four-membered heterocycles absorb little in the readily accessible UV regions. Sulfur-containing rings are an exception, as can be seen by inspection of Table 7. The UVVis spectra of dithiiranes reveal an absorption maximum in the range 435455 nm due to the SS bond <1995TL1867, 2003JOC1555, CHEC-III(1.14.3.1.2)649>, and this has been used to monitor the decomposition of dithiiranes <1995TL1867>. 

The best-known cyclic sulfur imides are saturated sulfur-nitrogen heterocycles, which are derived from cycler Ss by the replacement of one or more sulfur atoms by an amido (NH) group. Derivatives containing adjacent NH groups are not found. Thus, the members of this series consist of S7NH (70), three diimides 1,3-, 1,4- and 1,5-S6(NH)2, two triimides 1,3,5- and 1,3,6-85(NH)3, and S4N4H4 (71). 

Calorimetric and computational study of sulfur-containing six-membered rings including saturated S- and O-heterocycles 05CSR347. 

Antioxidative Activity of Thiazoiidine and 1,3-Ditiiiolane. Saturated cyclic sulfides represent another common class of sulfur-containing heterocyclic compounds formed in model systems and cooked foods. We have selected thiazoiidine and 1,3-dithiolane as model compounds for which to evaluate the antioxidative activity of this class of compounds and the results are shown in Figure 6. 1,3-Dithiolane appears to exhibit slightly higher activity than that of thiazoiidine. Both, however, inhibit heptanal oxidation for a longer period than do the thiophene derivatives presumably due to their different structural characteristics and hence potentially different mechanisms of antioxidative action. 

Figure 1 Saturated heterocycles containing oxygen or sulfur atoms in the 1,2,3-positions.

The species which are unknown and have not been identified as one of the major chemical lump such as alkanes, phenols and aromatics are lumped together as unidentified. However, the species in this lump include saturated and unsaturated cycloalkanes with or without side chains, which resembles the naphthenes, a petroleum refinery product group. A number of well known species in coal liquid are not mentioned in this lumping scheme. Such as heterocyclic compounds with sulfur, nitrogen or oxygen as the heteroatom, and other heteroatora containing species. Some of these compounds appear with aromatics (e.g. thiophenes, quinolines) and with phenols (e.g. aromatic amines), and most of them are lumped with the unidentified species lump. 

Coke-oven tar is an extremely complex mixture, the main components of which are aromatic hydrocarbons ranging from the monocyclics benzene and alkylbenzenes to polycyclic compounds containing as many as twenty or more rings. Heterocyclic compounds containing oxygen, nitrogen, and sulfur, but usually only one heteroatom per ring system are present. Small amounts of paraffinic, olefinic, and partly saturated aromatic compounds also occur. 

This chapter and the next two will revisit the ring theme, but the rings will all be heterocycles rings containing not just carbon atoms, but oxygen, nitrogen, or sulfur as well. It may seem strange that this rather narrowly defined class of compounds deserves three whole chapters, but you will soon see that this is justified both by the sheer number and variety of heterocycles that exist and by their special chemical features. Chapters 43 and 44 cover heterocycles that are aromatic, and in this chapter we look at heterocycles that are saturated and flexible. Some examples, a few of which may be familiar to you, are shown below and overleaf. 

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