Blue shifting hydrogen bonding in the complexes of chlorofluoro haloforms with acetone-d(6) and oxirane-d(4)

Mixtures of haloforms of the type HCClnF3-n (n = 0-3) with oxirane-d4 and acetone-d6 have been studied in liquid krypton, using infrared spectroscopy. Analysis of the spectra shows that a small fraction of the monomers is transformed into 1:1 complexes in which the haloform C-H bond is hydrogen bonded to the oxygen atom of the base. For all complexes, the haloform CH stretch is blue shifted, with the shift increasing from chloroform to fluoroform, while the ratio of the infrared intensities of the C-H stretching bands of complexed and free C-H bonds changes from a value well over 50 for the chloroform to a value near 0.1 for the fluoroform complexes. These observations have been corroborated by ab initio calculations using CP-corrected gradient techniques.