COMPUTATIONAL STUDY OF THE ROTATIONAL PATHWAYS OF THE AMINO GROUP IN 2-CHLOROANILINE, AZINES AND FORMAMIDE: ONE OR TWO ROTATIONAL BARRIERS?

Abstract

Rotation of the amino group in five different molecular systems, 2-aminopyridine, 2-aminopyrimidine, 2-chloroaniline, N-methylamino-1,3,5-triazine, and formamide, has been studied at B3LYP/6-3 11++G(2d,2p), MP2/6-311++G(2d,2p), and CCSD(T)/6-311++G(2d,2p)//B3LYP/6-311++G(2d,2p) levels of density functional, MP2, and coupled cluster theories. To this end, detailed rotation energy profiles for the above amino systems were obtained in two different ways: (1) by computing the energy-values as a function of only one torsion angle; and (2) by taking into account that the pyramidal nature of the NH2 group changes as rotation progresses so that energy profiles should be defined by two torsion angles. In the first case, saw-toothed energy profiles exhibiting two rotational barriers were always obtained. Conversely, by using two torsion angles as reaction coordinates smooth pathways were found where a rotation cycle can be completed passing only through the lowest energy barrier. Implications of these conflicting pathways are discussed