The molecular structure of N-methylsuccinimide studied by gas-phase electron diffraction (GED) and quantum-chemical methods

The molecular structure of N-methylsuccinimide was studied by the GED method at a nozzle temperature of 69–73°C. Anharmonic vibrational corrections to thermal-average r _a bond lengths, Δ(r _a − r _e), were calculated using the quadratic and cubic force constants from B3LYP/6-31G(df, p) calculations. The molecular skeleton was found to be planar within measurement errors. Some structural effects were likely caused by the conjugation of the N atom with two C=O bonds. The equilibrium geometric parameters derived from the experimental data and those from MP2/cc-pVTZ(seg-opt) calculations were in close agreement.