A cryospectroscopic study of the blue-shifting C–H⋯O bonded complexes of pentafluoroethane with dimethyl ether-d6, acetone-d6 and oxirane-d4

The infrared spectra of solutions of pentafluoroethane, CHF2CF3, and dimethyl ether-d6, acetone-d6, or oxirane-d4 dissolved in liquid krypton were investigated, at temperatures between 118 and 168 K. In all spectra, evidence was found for the formation of C–H⋯O hydrogen bonded complexes that are characterized by a blue shift in the C–H stretching fundamental. The shifts were found to be +15.1 cm−1 (dimethyl ether-d6), +24.3 cm−1 (acetone-d6) and +20.3 cm−1 (oxirane-d4), while the corresponding intensity ratios εcom/εmon were derived to be 0.35(1), 0.42(5) and 0.54(2). Using spectra recorded at different temperatures the complexation enthalpy ΔexpH∘ΔexpH∘ for the complexes were determined to be −12.1(1), −12.9(1) and −12.6(1) kJ mol−1, respectively. The results are compared with theoretical data obtained by combining ab initio complexation energies with thermal and solvent corrections obtained from statistical thermodynamical calculations and Monte Carlo-Free Energy Perturbation simulations. The results are also compared with experimental and theoretical data obtained for the complexes formed between the same proton acceptors and fluoroform.