Internal rotation of the hydroxyl group in isopropanol and the chirality of the gauche form: Fourier transform microwave spectroscopy of (CH3)(2)CHOD

The rotational spectrum of the deuterated isopropanol (CH3)(2)CHOD has been observed by Fourier transform microwave spectroscopy and analyzed to yield tunneling splitting of 4431.4613 (17) MHz, between the antisymmetric and t he symmetric gauche forms, which is much larger than the 2400 MHz estimated from the internal-rotation potential function reported in the literature. The potential function for the OH internal rotation has been examined in vi ew of the discrepancy between the observed and estimated tunneling splittin g, and it was accounted for by taking into account isotope effects on the p otential constants. The deuterium quadrupole coupling effect has been inclu ded together with the Coriolis terms in the off-diagonal block of the Hamil tonian matrix for the gauche form. The deuterium quadrupole coupling consta nts obtained for the trans form were employed to calculate the components o f the coupling constants as functions of the internal-rotation angle. and t he components at around 120 degrees were compared with the values observed for the gauche form, thereby leading to unambiguous determination of the si gns of the constants in the off-diagonal block; the signs are not obtainabl e from an ordinary anal;sis of the rotational spectra. The chirality of the gauche form was discussed by placing special emphasis on the effect of int ermolecular interactions between two chiral molecules. (C) 2001 Academic Pr ess.