Infrared spectra and configurations of alkylurea derivatives: Normal vibrations on N, N′-dimethyl- and tetramethylurea

Normal coordinate analyses of N, N′-dimethylurea and tetramethylurea were carried out employing a Urey-Bradley force field. The majority of the bands observed in the infrared spectra of alkylurea derivatives arise from mixed vibrations just as in secondary amides. Dialkylureas show evidence for the presence of rotamers with NH bonds cis and trans with respect to the carbonyl oxygen. The perturbations of the mixed vibration bands of alkylureas in charge-transfer as well as metal complexes are discussed.