Association of diphenylguanidine and quantum-chemical calculations of the structure of its cyclic dimers

The frequencies and intensities of the two tautomeric structures of the N,N'-diphenylguanidine monomer and its hydrogen-bonded cyclic dimers were calculated for structure elucidation of the monomer and dimer forms of this compound and identification of the stretching vibration band vNH of this molecule in solution. Ab initio HF/3-21G and B3LYP/6-31G(dp) calculations of DPG monomers and cyclic associates suggest that the asymmetric tautomer is dominant, proving that the dimer structures with two C=(Ph)N...H-NPh hydrogen bonds prevail in solution. An assignment of IR absorption frequencies of DPG in solution is suggested.