Imidazoles steric aspects

Secondary amines also yield linear polypeptides, when their nucleophilicity is not reduced by steric hindrance (e.g., dimethylamine or piperidine). Imidazole is an exception mainly yielding cyclic polypeptides. Cyclic polypeptides are also formed by sterically hindered secondary amines and by tertiary amines. Thermal polymerizations also yield cyclic polypeptides. Mechanisms and preparative aspects of aU these polymerizations are discussed in Chap. 15. 

---