Vibrational analysis of ethylamines: Trans and gauche forms |
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Authors: | Yoshiaki Hamada Kazuko Hashiguchi Akiko Y Hirakawa Masamichi Tsuboi Munetaka Nakata Mitsuo Tasumi Shigeki Kato Keiji Morokuma |
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Institution: | Faculty of Pharmaceutical Sciences, University of Tokyo, Hongo, Bunkyo-ku, Tokyo 113, Japan;Department of Chemistry, Faculty of Science, University of Tokyo, Hongo, Bunkyo-ku, Tokyo 113, Japan;Institute for Molecular Science, Myodaiji, Okazaki 444, Japan |
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Abstract: | Starting from force constant values calculated by an ab initio MO method (), and by adjusting the diagonal elements, a practical force constant matrix (F) has been reached which could explain the observed infrared and Raman spectra (in the frequency range lower than 2000 cm?1) of the gauche form of the ethylamine CH3CH2NH2 molecule and five isotopic species CH313CH2NH2, CH3CH215NH2, CH3CD2NH2, CH3CH2ND2, and CD3CD2NH2. The F matrix for the trans form of ethylamine was constructed by transferring ab initio values and by revising diagonal elements with conversion factors whose values are equal to the corresponding values of gauche form. A nearly complete set of assignments was achieved of the vibrational bands of ethylamines, observed so far in the spectral range 2000–100 cm?1. In matrix isolation spectroscopy, two bands assignable to the NH2 wagging vibrations of gauche and trans forms have been found at 775 and 782 cm?1, respectively, for CH3CH2NH2. They are at 768 and 774 cm?1, respectively, for CD3CD2NH2. From the intensity changes of these bands observed on changing the nozzle temperature in the matrix formation, the energy difference ΔE (gauche-trans) of these two conformers has been estimated to be 100 ± 10 cm?1. |
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