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

The molecular structure of N,N-dimethyiactamide, (CH3)(2)NC(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 Sigma alpha(N) = 354.1(17)degrees. 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 3 sigma values) were derived from the GED analysis: C1=0 = 1.226(3) Angstrom, C1-C2 = 1.527(6) Angstrom, N-C1 = 1.368(5) Angstrom, N-C3 = N-C4 = 1.453(3) Angstrom, N-C1=O= 121.0(7)degrees, N-Cl-C2 = 115.9(9)degrees, C1-N-C3 = 123.8(13)degrees, C1-N-C4 = 117.8(11)degrees (C3 and C4 are anti and syn to oxygen, respectively, and the N-C3 and N-C4 bond lengths were assumed to be equal).