Alternating 1-Phenyl-2,2,2-Trifluoroethanol Conformational Landscape With the Addition of One Water: Conformations and Large Amplitude Motions

The 1:1 adduct of 1-phenyl-2,2,2-trifluoroethanol (PhTFE), a chiral fluoroalcohol, with water was investigated using chirped pulse Fourier transform microwave spectroscopy and computational methods. 'While PhTFE itself was predicted to have three minima, I (gauche+), II (trans), and III (gauche-), only I and II were stable and only I was observed experimentally. A systematic search of the PhTFE center dot center dot center dot H2O conformational landscape identified 110 stable minima, 14 of which are within a 15 kJ mol(-1) energy window. Rotational spectra of the two PhTFE center dot center dot center dot H2O conformers along with several deuterium and O-18 isotopologues were assigned, and the isotopic data were used to verify the corresponding structures. In the two observed monohydrate conformers, one contains PhTFE I where the water subunit is inserted into the existing intramolecular OH center dot center dot center dot F contact of I, and the binary adduct is stabilized by two intermolecular contacts: OH center dot center dot center dot O-w and H-w center dot center dot center dot F, whereas the other contains PhTFE II where the water subunit interacts with both the alcohol hydrogen and phenyl ring of II, demonstrating that interaction with water sufficiently stabilizes II for its observation in a jet expansion. Interestingly, the predicted electric dipole moment components at the identified minima deviate considerably from the experimental ones. Such deviations were analyzed in terms of dynamic effects associated with the large amplitude motions of the unbound H-w. In addition, tunnelling effects associated with the exchange of the bonded and nonbonded H-w were also discussed.