15min:

TAIGO UZUYAMA, YUGO TANAKA AND YOSHIYUKI KAWASHIMA, Department of Applied Chemistry, Faculty of Engineering, Kanagawa Institute of Technology, Atsugi, Kanagawa 243-0292, JAPAN; EIZI HIROTA, The Graduate University for Advanced Studies, Hayama, Kanagawa 240-0193, JAPAN.

We have investigated two butanols, normal (1-butanol) and iso (2-methyl-1-propanol), by Fourier transform microwave spectroscopy, focusing attention mainly to internal motion and rotational isomerism. We anticipate that n-butanol exists in fourteen rotational isomers with the combination of the following conformations: trans (T) and gauche (G) with respect to the CH₃CH₂-CH₂CH₂OH bond, trans (t) and two gauche's (g, g') to the CH₃CH₂CH₂-CH₂OH bond, and two or three potential minima in the internal rotation of OH, and that isobutanol in five. We scanned the frequency region from 7 to 25 GHz using a heated nozzle, and detected six and three isomers for n-butanol and isobutanol, respectively: three with Ar as a buffer gas and three with Ne instead of Ar for n-butanol, whereas Ar was employed for isobutanol. The observed spectral lines were assigned by comparing the experimental moments of inertia and the observed spectral intensities with those calculated by ab~ initio MO at the MP2/6-311++G(d,p) level. We thus concluded that five conformers detected for n-butanol are T-form and one G-form and that three observed isomers of isobutanol are gauche with respect to the H(CH₃)₂C-CH₂OH bond and one isomer lacking a-type spectra to trans to the CH₂-OH bond.