ROTATION INVERSION STUDY OF THE AMINO GROUP IN ETHYLAMINE/

Using the HF, MP2, and DFT methodologies in the GAUSSIAN 94 set of qua ntum chemistry codes with a 6-311G* basis set, we examine theoretical ly the internal rotation and inversion of the amino group in ethylamin e. An analytical potential energy surface corresponding to energy as a function of phi, the dihedral angle of the lone-pair of electrons on the amino group, and tau, the angle between the amine plane and the C- N axis, for these motions is generated by fitting the energy determine d at 109 geometries to sums of products of Bessel functions of the fir st kind, J(m), and cos(m phi). The surface depicts several special poi nts: the minimum energy trans conformer, the two gauche conformers, th e three first-order transition states for internal rotation of the ami no group about the C-N bond, the two first-order transition states for the inversion of the amino group, and the three second-order transiti on states also for the inversion motion. The results of a related stud y on the internal rotation of the ammonium group about the C-N bond in the ethylammonium ion are also interspersed in this report. Both nond euterated and several deuterated isotopomers of both ethylamine and et hylammonium ion are considered.