Planarity of N,N-Dimethylacetamide, (CH₃)₂NC(O)CH₃

Abstract

The molecular structure of N,N-dimethylactamide, (CH3)2NC(O)CH3, was determined by gas electron diffraction (GED). A rigid model results in a vibrationally averaged structure with nonplanar configuration at nitrogen and with the sum of the nitrogen bond angles ∑αN = 354.1(17)°. The GED intensities can be fitted equally well with a dynamic model with either a quartic potential (planar equilibrium structure) or a very flat double-minimum potential (pseudoplanar structure) for the out-of-plane motion. Theoretical calculations predict either planar (HF/3-21G and B3PW91/6-311G(2d)) or slightly nonplanar equilibrium structures (HF/3-21G(*), MP2/6-31G*, and MP2/6-311G*). The following skeletal parameters (uncertainties are 3σ values) were derived from the GED analysis: C1O = 1.226(3) Å, C1−C2 = 1.527(6) Å, N−C1 = 1.368(5) Å, N−C3 = N−C4 = 1.453(3) Å, N−C1=O = 121.0(7)°, N−C1−C2 = 115.9(9)°, C1−N−C3 = 123.8(13)°, C1−N−C4 = 117.8(11)° (C3 and C4 are anti and syn to oxygen, respectively, and the N−C3 and N−C4 bond lengths were assumed to be equal).