Hydrogen bonding in the gas phase. Infrared spectroscopic investigation of hydrogen fluoride alcohol–heterodimers

Abstract

For the first time, an infrared investigation of gas phase hydrogen bonded complexes formed by hydrogen fluoride with alcohols has been made, Evidence has been given for the formation of 1 : 1 heterodimers ROH HF and the vibration wavenumbers Y(F-H) have been estimated. The wavenumber displacements of the HF stretching vibration on H bond formation provide a measure of the electron donating abilities in the free alcohols. The electron donating power of the oxygen atom is increased by increasing methylation at the oxygen atom, as indicated by the constant increase of 75 cm-' in AGF along the series H 2 0 HF, CH30H HF, (CH3)ZO HF. A similar but attenuated increase occurs on increasing methylation of the carbon atom in methanol as indicated by steps of about 25 cm-I in A ~H F for complexes formed by CH30H, CH3CH20H, (CH,),CHOH and (CH&COH. On the other hand, the electron donating ability of the oxygen atom is decreased by the presence of the electron attracting groups CH2Cl, CH2F and CF3. We confirm that where the vapour pressure of a component is a limitation on observing dimer formation in the gas phase, as is the case in most alcohols, it is advantageous to work at higher temperatures.

Electron Photodetachment Spectroscopy of Solvated Anions: RO·HF-or ROH·F-?

“…Analyzing the shifts in the stretching vibrations Thomas predicted that the methanol-HF and the ether-HF bonds are stronger than the H 2 O‚HF bond. From infrared experiments Legon 60 suggests that the ROH‚HF binding energy is stronger than the binding energy in H 2 O‚HF. Based on the analysis given above we believe that the ROH‚HF binding energy is equal to or greater than 10.3 kcal mol -1 ; we use 10.3 kcal mol -1 in our subsequent analysis.…”