The effect of ring size in N-benzoyl saturated heterocyclic amides

The structures of the N-benzoyl derivatives of aziridine, azetidine, pyrrolidine, piperidine, hexamethyleneimine and heptamethyleneimine in solution have been investigated by 13C n.m.r. spectroscopy. In conjunction with literature crystal structure and dynamic intramolecular exchange data, it has been concluded that N-benzoylaziridine and N-benzoylazetidine possess pyrimidal nitrogen atoms in solution. The N-benzoyl derivatives of pyrrolidine,  piperidine, hexamethyleneimine and heptamethyleneimine have planar or near planar nitrogen atoms.