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.