Ab initio Studies on Hydrazines: 1H-Pyrrol-1-amine (N-Aminopyrrole)

Abstract

The geometries of four stationary structures of 1H-pyrrol-1-amine have been optimized with the 3-21G and 3-21G(N*) basis sets. The lowest- energy and only equilibrium structure is the 'perpendicular' C_S form (4) in which a pyramidal NH₂ group is bisected by the plane of the pyrrole ring. The transition structure for inversion at the NH₂ group is the perpendicular C_2V form (2). After zero-point vibrational -energy corrections, it lies 24.5 kJ mol^-1 [3-21G(N*)] above (4). The transition structure for rotation about the N-NH₂ bond is the 'parallel' C_S form (3) in which a plane of symmetry bisects both the pyrrole ring and the attached pyramidal NH₂ group; it lies 26.5 kJ mol^-1 above (4). The planar C_2V structure (1) is a second-order saddle point lying 69.4 kJ mol^-1 above (4). The spacing of NH-stretching frequencies calculated for the equilibrium structure (4) of 1H-pyrrol-1-amine is in the range for normal primary amines, unlike that for 1,1-dimethylhydrazine.