Intramolecular noncovalent force in cyclic amidines: nonbonded interaction between carbon atoms and heteroatoms

A set of four new cyclic amidines has been synthesized and characterized. A novel intramolecular noncovalent force between carbon atoms of the aromatic ring and heteroatoms of cyclic amidines has been demonstrated and established by X-ray structural analysis and ab initio calculation at B3LYP/6-31G* level. This new noncovalent force is presumably caused by an orbitalic overlap between the σ* or π* orbital of one aromatic carbon–carbon bond and one lone pair of electrons of the involved heteroatom. The generality of these interactions in organic compounds has been corroborated exploring the Cambridge Structural Database.