Why N-methyleneformamide, CH2N-CHO, prefers gauche-conformation? A DFT/NBO study

Three possible stable conformations of N-methyleneformamide were studied using Weinhold's Natural bond orbital method. Wavefunctions for the NBO analysis were obtained using B3LYP hybrid functional with 6-311+G(d,p) extended basis set. gauche conformation was predicted to be more stable than trans conformation by ≈2.3 kcal/mol in agreement with earlier studies. At the same time it was found that this preference is due to the strong πC1-N2↔πC3-O4 and σC3-H5↔nσN2 repulsive interactions in the planar conformations, and additional conjugative stabilization of the gauche conformation.