Unsaturated Sulfur-Nitrogen Rings

Tt-Electron-rich compound a compound in which the number of tt-electrons exceeds the number of atoms Heterocyclothiazene an unsaturated sulfur-nitrogen ring system containing another element... 

Some of the newer compounds may contain both saturated and unsaturated rings, heteroatoms such as oxygen, nitrogen, or sulfur, and halogen substituents. Others, such as synthetic pyrethroids, may have one or more chiral centers, often needing stereospecific methods of synthesis or resolution of isomers (42). Table 4 Hsts examples of some more complex compounds. Stmctures are shown ia Eigure 1 (25). 

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... 

Chromatography has also been used to separate the unsaturated phos-phorus(V)-nitrogen-sulfur ring systems 3.4—3.6. " The six-membered ring... 

Figure 12 Six-membered monocyclic systems containing multiple nitrogen, oxygen, and/or sulfur atoms (names shown correspond to rings with maximum unsaturation).

A heterocycle is a compound with a ring that has more than one kind of atom. Nitrogen, oxygen, and sulfur are often found along with carbon in heterocyclic rings. Saturated heterocyclic amines, ethers, and sulfides usually have the same chemistry as their open-chain analogs, but unsaturated heterocycies such as pyrrole, furan, and thiophene are aromatic. All three are unusually stable, and all three undergo aromatic substitution on reaction with electrophiles. 

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