Trivalent atoms, isosterism

The substitution of —CH= by —N= in aromatic rings has been one of the most successful applications of classical isosterism (see Section III.D.). Interchange of trivalent atoms are found also in non aromatic rings. For example the 4-dimethylamino-antipyrine and its carba-isostere are about equally active as antipyretics (Figure 15.7). 

Equally important isosteric replacements involve trivalent atoms and groups. These include -N= and -C=, especially in ring compounds, and they will be discussed in the appropriate chapters. 

---