The microwave and far-infrared spectra and the geometry of 8-oxabicyclo[3.2.1]octane

The structure of 8-oxabicyclo[3.2.1]octane was calculated by abinitio means at the STO-3G level, and the structural data used to assign the microwave spectrum of the title compound in the range of 26.5 to 40 GHz fitting 144 lines up to J = 48 by adjusting the rotational and three centrifugal distortion constants in the Watson A reduction. Structural parameters were deduced from the rotational constants by allowing all bond lengths and angles to vary in a least-squares manner. These parameters were in good agreement with those calculated at the STO-3G and 3-21G levels. Of many satellite lines observed, only the most intense could be utilized for locating the two lowest fundamental vibrations, estimated to occur at 190 and 240 cm−1. The far-infrared spectrum is reported in the region of 80 to 300 cm−1, exhibiting only one distinct sequence of Q branches at 264 cm−1. On the basis of unsealed abinitio force fields at both levels of the theory the corresponding fundamentals are assigned, respectively, to a twisting (A″) and a bending (A′) of the cycloheptane ring. Keywords: 8-oxabicyclo[3.2.1]octane, microwave and far-infrared spectra, abinitio STO-3G and 3-21G geometries.