Oxygen sulfur rings

The organic chemical structural types believed to be characteristic of coals include complex polycyclic aromatic ring systems with connecting bridges and varied oxygen-, sulfur-, and nitrogen-containing functionalities. 

Calculation of group increments for oxygen, sulfur and nitrogen compounds has allowed the estimation of conventional ring-strain energies (CRSE) for saturated heterocycles from enthalpies of formation. For 1,3-dioxolane, CRSE is about 20 kJ mol . In 2,4-dialkyl-l,3-dioxolanes the cis form is always thermodynamically the more stable by approximately 1 kJ mol" . 

This section treats seven-membered ring systems with maximum unsaturation containing within the ring two or more oxygen, sulfur or nitrogen atoms, or a combination of these.1... 

A number of lower sulfur oxides have been described. Most of these oxides are derived from cyclic sulfur polymorphs and were usually prepared by oxidation of these molecules by organic peroxo acids. The oxides have the general formula SraO and n may vary from 5 to 10. For n = 7 even the dioxide S702 is known.4 Not all of these phases were characterized by X-ray diffraction, but the molecular structures are certain with respect to vibrational spectroscopy. The oxygen atom is in exo position with respect to the sulfur ring as it has been shown by X-ray diffraction for SgO and S70, respectively (Figure 2).5,6... 

CARBON-NITROGEN-OXYGEN/SULFUR-METAL RINGS... 

Ring Synthesis of Fused Pyridazines, Pyrimidines, and Pyrazines with Oxygen, Sulfur,... 

In Scheme 1, all the ring systems belonging to this chapter are depicted. The six-membered rings can be oxazine, thiazine, pyridazine, pyrazine, and pyrimidine, whereas the five-membered fused ring can contain oxygen, sulfur, selenium, phosphoms, and nitrogen atoms in various arrangements. 

Reactivity of ring oxygen and ring sulfur atoms 912... 

Synthesis of Ring Systems Implying Also Oxygen, Sulfur, or Phosphorus Atoms 913... 

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