The conformation of ethylenurea from microvawe spectroscopy and ab initio computations

The conformation of ethyleneurea has been investigated using microwave spectroscopy and ab initio computations. The molecule is found to have a C2 symmetry equilibrium conformation with a non-planar ring and non-planar geometries at the nitrogen atoms. Both the inertial data and ab initio computations show that the amide hydrogen atoms occupy equatorial positions. The observation of inversion splittings on ground vibrational state ?aQ-branch lines indicates an inversion barrier of ~6-8 kJ mol-1. The computed energy difference between the planar ring molecule and the equilibrium conformation is 7.2 kJ mol-1 using a 6.31 G** orbital basis. A second conformer with Cs symmetry is computed to have an energy of 0.2 kJ mol-1 less than that of the planar ring molecule.