Conformational study of benzene-fused ring compound 1,2,3,4-tetrahydronaphthalene using vibrational laser spectroscopy

Abstract

The infrared, Raman, and jet-cooled laser-induced fluorescence excitation spectra of 1,2,3,4-tetrahydronaphthalene have been recorded and analyzed. The observed vibrations have been assigned to understand the conformational behaviors in its electronic ground (S-0) and excited (S-1) states. Ab initio at the HF/6-31G** level and molecular mechanics (MM3) force field calculations have been carried out to generate the complete normal mode frequencies of the molecule in its So state. The vibrational frequencies calculated from the ab initio method show a better agreement with the observed infrared and Raman frequencies than those calculated from the MM3 method. In several cases, the normal mode calculations were very helpful to clarify some ambiguities of previous assignments. In addition, the ring inversion process between two twisted conformers of 1, 2,3,4-tetrahydronaphthalene has been reexamined utilizing ab initio calculation. The results show that the ring inversion energy is in the range of 3.7-4.3 kcal/mol which is higher than the previously reported AM1 value of 2.1 kcal/mol.