Conformations of 2-aminoindan in a supersonic jet: the role of intramolecular N-H...pi hydrogen bonding.
Laser-induced fluorescence (LIF), dispersed fluorescence (DF), mass-resolved one-color resonance enhanced two-photon ionization (RE2PI) and UV-UV hole-burning spectra of 2-aminoindan (2-AI) were measured in a supersonic jet. The hole-burning spectra demonstrated that the congested vibronic structures observed in the LIF excitation spectrum were responsible for three conformers of 2-AI. The origins of the conformers were observed at 36931, 36934, and 36955 cm(-1). The DF spectra obtained by exciting the band origins of the three conformers showed quite similar vibrational structures, with the exception of the bands around 600-900 cm(-1). The molecular structures of the three conformers were assigned with the aid of ab initio calculations at the MP2/6-311+G(d,p) level. An amino hydrogen of the most stable conformer points toward the benzene ring. The stability of the most stable conformer was attributed to an intramolecular N-H...pi hydrogen bonding between the hydrogen atom and the pi-electron of the benzene ring. The other two conformers, devoid of intramolecular hydrogen bonding, were also identified for 2-AI. This suggests weak hydrogen bonding in the most stable conformer. The intramolecular N-H...pi hydrogen bonding in 2-AI was discussed in comparison with other weak hydrogen-bonding systems.
Iga
Hiroshi
H
Department of Chemistry and Materials Science, Tokyo Institute of Technology, 2-12-1 Ohokayama, Meguro-ku, Tokyo 152-8551, Japan.
Isozaki
Tasuku
T
Suzuki
Tadashi
T
Ichimura
Teijiro
T