Vibrational spectra and structure of small ring compounds–XXII

Abstract

The i.r. spectra of cyclopentanol, α-cyclopentanol-d1 and β,β,β',β'-cyclopentanol-d4 in the liquid and gaseous states have been recorded from 300–4000 cm−1. The far-i.r. spectra of gaseous cyclopentanol, cyclopentanol-O-d, and cyclopentanol-d4 have been measured down to 33 cm−1. The i.r. spectra of polycrystalline cyclopentanol and cyclopentanol-O-d have been recorded from 33–300 cm−1. The Raman spectra of each species have been recorded and depolarization values measured for the normal molecule. The 42 fundamental vibrations have been assigned on the basis of group frequency correlations, isotopio shift ratios, and relative band intensities. The O-H torsional and radial modes were centered at 260 and 188 cm−1, respectively, in the spectrum of the isolated molecule but shifted to 737 and 258 cm−1 in the spectrum of the solid. Although no pseudorotational transitions were observed for gaseous cyclopentanol, a band at 122 cm−1 in the spectrum of the solid was assigned to this low frequency ring-puckering fundamental. If a frequency shift upon condensation similar to that observed for the radial mode is postulated for the pseudorotational fundamental, the 1 ← 0 transition for the isolated molecule must be lower than 50 cm−1. Such a low frequency, of course is consistent with a relatively small barrier to pseudorotation.