The microwave spectrum and OH internal rotation dynamics of gauche-2,2,2-trifluoroethanol

Abstract

Articles you may be interested inStructure and tunneling dynamics in a model system of peptide co-solvents: Rotational spectroscopy of the 2,2,2trifluoroethanolwater complex A comparison of the properties of 2,2,2-trifluoroethanol and 2,2,2-trifluoroethanol/water mixtures using different force fieldsThe microwave spectra of CF 3 CH 2 OH and CF 3 CH 2 OD have been investigated from 5 to 26 GHz with a pulsed-nozzle Fourier-transform microwave spectrometer and from 26 to 42 GHz with an electric resonance optothermal spectrometer. Tunneling of the OH proton between the two isoenergetic gauche conformations splits the observed transitions into two tunneling components. An effective rotation-tunneling Hamiltonian is used to fit the a-and b-type pure rotational and c-type torsional-rotational transitions for both isotopomers to better than 5 and 13 kHz for the OH and OD forms, respectively. The tunneling splittings determined from the fits for the OH and OD isotopomers are 5868.6952͑16͒ and 208.5037͑42͒ MHz, respectively. A structural analysis using the moments of inertia of the OH and OD isotopomers determines that the hydroxyl hydrogen is directed toward the fluorine with a F•••H separation of 2.561͑1͒ Å and a dihedral angle of ͑CCOH͒ϭ68.97͑6͒°. The observed tunneling splittings are fit to a double-minimum potential, giving gauche-gauche tunneling barriers of 763 and 720 cm Ϫ1 and OH torsional fundamental frequencies of 364 and 271 cm Ϫ1 for CF 3 CH 2 OH and CF 3 CH 2 OD, respectively. The uncertainties shown in parentheses throughout the paper are one standard deviation.

Chirality Recognition between Neutral Molecules in the Gas Phase

“…The monomer oscillates between the two enantiomeric gauche forms with a 170 ps period, which is much slower than for ethanol [195] but orders of magnitude faster than MFE because the process is largely limited to hydrogen atom motion. Two different hydrogenbond topologies can be realized in the dimer.…”

Transition State for β-Elimination of Hydrogen from Alkoxy Groups on Metal Surfaces

“…The favored conformations of the fluoroethanols all have oxygen synclinal with a fluorine, again in conformity with experiment, with the O-H hydrogen directed toward a fluorine. [17][18][19] …”

“…The favored geometry of gaseous trifluoroethanol, for instance, brings the O-H group close to one of the fluorine atoms, with a hydrogen-fluorine distance of 2.56 Å. 9 The analogous structure does not seem realistic for a trifluoroethoxy group adsorbed on a surface. Imposition of appropriate conformational constraints on the gas-phase ethanols reveals a correlation between the ∆H rxn for gas-phase dehydrogenation and the ∆E act for -hydrogen elimination in ethoxy groups.…”

Conformational stability, r 0 structural parameters, barriers to internal rotation, ab initio calculations, and vibrational assignment for 2,2-difluoroethanol

“…For comparison of the structural parameters obtained in this study for 2,2-difluoroethanol, we first tried the reported [20] values for gauche 2,2,2-trifluoroethanol but soon found that the assumed parameter for the C-C bond was much too short by at least 0.020 Å since it was transferred from the carbon-carbon distance for 1,1,1-trifluoroethane [21]. With the OH group placed on the other end of the CF 3 CH 3 molecule, the CC bond of trifluoroethanol is expected to be much longer.…”

“…[4]; calculated values from structural parameters in Table 4 c Experimental rotational constants Ref. [20]; calculated values from structural parameters in Table 9 Fig in frequency but with an A(55%)/C(40%) hybrid band and a predicted intensity of 28.3 km/mol. There appears to be one band at 489 cm -1 with either a B/C or A/C contour but the intensity is significantly larger than 8.4 km/mol as predicted for the Gg form so it is most reasonable to assign it as arising from both conformers although there is a relatively weak C-type band at 515 cm -1 , which could be m 17 for the Tg conformer.…”