| Abstract
| - Theoretical studies are performed on enflurane (CHFCl−CF2−O−CHF2) to investigate the conformationalproperties and vibrational spectra. Calculations are carried out at the B3LYP/6-31G(d) level along with anatural bond orbital (NBO) analysis. Experimental infrared spectra are investigated in carbon tetrachloridesolution at room temperature and in argon matrix at 12 K. In agreement with previously reported data (Pfeiffer,A.; Mack, H.-G.; Oberhammer, H. J. Am. Chem. Soc. 1998, 120, 6384), it is shown that the four most stableconformers possess a trans configuration of the C−C−O−C skeleton and a gauche orientation of the CHF2group (with respect to the central C−O bond). These conformations are favored by electrostatic interactionbetween the H atom of the CHF2 group and the F atoms of the central CF2 group. Hyperconjugation effectsfrom the O lone pairs to the antibonding orbitals of the neighboring C−H and C−F bonds also contribute tothe stability of the four conformers. The vibrational frequencies, infrared intensities, and potential energydistributions are calculated at the same level of theory for the most stable conformers. On the basis of thetheoretical results, these conformers are identified in an argon matrix. The influence of the concentration onthe ν(CH) vibrations suggests the formations of higher aggregates in solution. Theoretical calculations arecarried out on the enflurane dimer. The results show that the dimer is formed between two enflurane conformershaving the largest stability. The dimer has an asymmetric cyclic structure, the two enflurane molecules beingheld together by two nonequivalent C−H···F hydrogen bonds, the C−H bond of the CHFCl group acting asa proton donor, and one of the F atoms of the CHF2 groups acting as a proton acceptor. The theory predictsa contraction of 0.0014−0.0025 Å of the two CH bonds involved in the interaction along with a blue shiftof 30−38 cm-1 of the corresponding ν(C−H) bands, in good agreement with the blue shifts of 35−39 cm-1observed in an argon matrix.
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