Pseudorotation pathway and equilibrium structure from the rotational spectrum of jet-cooled tetrahydrofuran

Abstract

Articles you may be interested inRotational spectra of rare isotopic species of fluoroiodomethane: Determination of the equilibrium structure from rotational spectroscopy and quantum-chemical calculations Internal dynamics features in the free jet rotational spectrum of the acetaldehyde-Kr molecular complexThe rotational spectrum of jet-cooled tetrahydrofuran has been investigated in the 8-18 and 60-78 GHz frequency ranges. Only the four lowest vibrational levels remain populated in the jet conditions. Two pseudorotation vibrational spacings have been measured directly to be ⌬E 01 ϭ21 307.71(3) MHz and ⌬E 23 ϭ61 205.69(3) MHz. They have been used, together with the lowest 10 measured far infrared transition frequencies and with the effective moments of inertia of the ground state and their shifts upon excitation observed in this work, to determine the potential energy function for pseudorotation and the associated structural relaxations. The potential energy barriers are 45 cm Ϫ1 at the envelope conformation of the oxygen and 16 cm Ϫ1 at the twisted conformation of the C ␤ -C ␤ Ј bond relative to the C ␣ OC ␣ Ј plane. The four symmetrically equivalent equilibrium structures are close to the envelope conformations of the CH 2 groups next to the oxygen atom. While the C-O bond lengths and the local CH 2 angles appeared to remain unaffected by pseudorotation, significant changes found for the diagonal O•••C distances as well as for the C-C and C-H bond lengths are of interest as possible effects of hyperconjugation.

Extension of the Karplus Relationship for NMR Spin-Spin Coupling Constants to Nonplanar Ring Systems: Pseudorotation of Tetrahydrofuran

“…However, microwave studies by Engerholm and co-workers [20] carried out in the late 60ies and recently repeated and extended by Meyer and co-workers [21] suggest a fourfold pseudorotational potential (V 4l coefficients dominate the CES function (5) rather than the V 2l coefficients) with equivalent minima at φ = 0 ± 52.5…”

“…Because of its importance as a model for ribofuranose, THF has been extensively investigated by various experimental techniques ranging from far-infrared spectroscopy [18,19] and microwave spectroscopy [20,21] to electron diffraction [22], X-ray [23], and neutron diffraction techniques [24]. In addition, there are several quantum chemical investigations [25,26] and molecular mechanics (MM) studies [27,28], which have focused on the conformational features of THF.…”

Valence orbital response to pseudorotation of tetrahydrofuran: A snapshot using dual space analysis

“…However, a general consensus about the minimum energy structure of this molecule has not been achieved yet. While Engerholm et al 12 and Meyer et al 13 proposed a potential function for pseudorotation in THF with four equivalent minima 14 and Melnik et al 8 reported that the twisted ␤ T ␤ Ј ͑C 2 ͒ and ␤ T ␤Ј ͑C 2 ͒ conformations represent two equivalent global minima structures for THF. The previous work illustrates the enormous difficulties associated with the conformational analysis of the THF.…”

“…The previous work illustrates the enormous difficulties associated with the conformational analysis of the THF. Indeed, after about 40 years of both theoretical and experimental research, 6,8,[12][13][14] the question of the equilibrium geometry of THF has not been resolved.…”

“…6,8,9,[12][13][14][15][16] Rayón and Sordo 7 stressed the fact that since the energy differences between the involved structures are so small, special care should be exercised when choosing an appropriate computational level to deal with the extremely difficult conformational problem of pseudorotation in THF.…”