Pseudorotation motion in tetrahydrofuran: An ab initio study

Abstract

The use of different models based on experimental information about the observed level splitings, rotational constants, and far-infrared transition frequencies leads to different predictions on the equilibrium geometry for tetrahydrofuran. High-level ab initio calculations [coupled cluster singles, doubles (triples)/complete basis set (second order Moller-Plesset triple, quadrupole, quintuple)+zero-point energy(anharmonic)] suggest that the equilibrium conformation of tetrahydrofuran is an envelope C(s) structure. The theoretical geometrical parameters might be helpful to plan further microwave spectroscopic studies in order to get a physical interpretation of the measurements.

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

“…19 They found the most populated conformer of this molecule in the gas phase under the experimental conditions to be the C s conformer, in agreement with the high level ab initio predictions. 7 In the present work, we extend previous studies on THF by reporting the results of comprehensive quantum mechanics ͑QM͒ orbital MD simulations of the individual outer valence orbitals of this molecule. As some of the orbital MDs of THF are not yet fully resolved by experiment, 18 the present study will provide additional information that might well help to complement the experimental work.…”

“…Hessian calculations showed that both C s and C 2 structures have all positive frequencies, suggesting that they could be characterized as minimum configurations on the PES. 7,18 The C 1 conformation resulted in negative frequencies, 18 indicating that it is a transition structure connecting the C s and C 2 minima structures. The 6-311+ + G ** basis set was chosen because it appears to give good geometric properties in combination with DFT models, whereas reduced bases, such as Pople's standard 6-31G * basis set, seem not to be appropriate in some cases.…”

“…5 Since geometrical changes and energy variations accompanying conformational motions for a given molecule can be rather small, determination of the most stable structure can become an extraordinarily difficult task. [6][7][8] This is indeed the case for tetrahydrofuran ͑THF͒, a heterocyclic fivemembered ring which can be regarded as a prototypical structural unit of, say, carbohydrate and biological molecules. 9 Thus, for example, a derivative of THF, azidothymine, is commonly recognized as the first anti-AIDS drug used in antiviral chemotherapy and prophylaxis in the United States.…”

“…Because of the complexities and subtleties associated with obtaining and analyzing position space ͑energy͒ information, 7 it has been shown to be beneficial to examine the problem in a different way. To that end, information from momentum space ͓momentum distributions or ͑MDs͔͒ can be very valuable.…”

“…More recently, a theoretical study, in which geometry optimizations were carried out at the MP2/aug-cc-pVTZ level, has been published. 7 The energy predictions were estimated through CCSD͑T͒/cc-pVTZ single-point calculations, extrapolated to the complete basis set ͑CBS͒ limit 17 by means of a series of MP2/cc-pVXZ ͑X = T , Q ,5͒ calculations and consideration of anharmonic contributions ͓CCSD͑T͒ / cc-pVTZ//MP2 / cc-pVTZ+ CBS͑MP2-TQ5͒ + ZPE͑anharmonic͒ level͔. Such a high level ab initio methodology predicted a PES like the one presented in Fig.…”