Association structures of N-methylacetamide in solution studied by infrared electroabsorption spectroscopy

Aggregated structures of N-methylacetamide in 1,4-dioxane solution have been studied using infrared electroabsorption spectroscopy. Predominance of two structures, the monomer and dimer, is demonstrated. For the monomer, angles α between the permanent dipole moment and the transition dipole moments are determined to be 6°±9° for the amide A, 0°±13° for the amide I, 62°±4° for the amide II modes, respectively. For the dimer, the experimental results are explained very well by assuming a head-to-tail structure, which has the permanent dipole moment twice as large as that of the monomer and similar α values as those of the monomer.