Rotation/Inversion Study of the Amino Group in Ethylamine

• Published in: The journal of physical chemistry. A, Molecules, spectroscopy, kinetics, environment, & general theory Molecules, spectroscopy, kinetics, environment, & general theory, 1998-08, Vol.102 (32), p.6571-6579
• Main Authors: Zeroka, Daniel, Jensen, James O, Samuels, Alan C
• Format: Article
• Language: English
• ISSN: 1089-5639; 1520-5215
• DOI: 10.1021/jp982031a

Using the HF, MP2, and DFT methodologies in the GAUSSIAN 94 set of quantum chemistry codes with a 6-311G** basis set, we examine theoretically the internal rotation and inversion of the amino group in ethylamine. An analytical potential energy surface corresponding to energy as a function of φ, the dihedral angle of the lone-pair of electrons on the amino group, and τ, the angle between the amine plane and the C−N axis, for these motions is generated by fitting the energy determined at 109 geometries to sums of products of Bessel functions of the first kind, J m, and cos(mφ). The surface depicts several special points:  the minimum energy trans conformer, the two gauche conformers, the three first-order transition states for internal rotation of the amino group about the C−N bond, the two first-order transition states for the inversion of the amino group, and the three second-order transition states also for the inversion motion. The results of a related study on the internal rotation of the ammonium group about the C−N bond in the ethylammonium ion are also interspersed in this report. Both nondeuterated and several deuterated isotopomers of both ethylamine and ethylammonium ion are considered.