Conformational behavior of N-methylformamide in the gas, matrix, and solution states as revealed by IR and NMR spectroscopic measurements and by theoretical calculations

The cis–trans isomerism of N-methylformamide has been reexamined by IR and NMR spectroscopic methods with the help of relatively high level DFT calculation. The occurrence of the cis-form in the amide molecule has been verified undoubtedly and the abundance of the cis-form as a minor component was determined to be about 5% in the gas phase at room temperature. The IR spectral features have been characterized by using a reliable set of force constants given by the DFT calculation. The evidence for the existence of the aggregation in low-temperature matrix and even in the gas phase has been given, and a preliminary consideration on the conformations of the dimers has been made. The concentration dependence of the NMR chemical shifts has been analyzed, and we found that the cis-form persists in solution at any concentration.