Exploring a hydrogen-bond terminus: spectroscopy of eucalyptol-alcohol clusters

Abstract

The influence of eucalyptol, a bicyclic ether, on the hydrogen bond aggregation of methanol (MeOH) and 2-methyl-2-propanol (BuOH) is investigated by ragout-jet FTIR techniques. O-H stretching bands of supersonic jet cooled binary complexes are identified and compared to spectra of liquid mixtures and quantum chemical predictions. Experimental O-H stretching wavenumber shifts of mixed alcohol-eucalyptol dimers exceed those of the corresponding alcohol dimers by 76 cm(-1) (MeOH) and 27 cm(-1) (BuOH). Harmonic predictions of the wavenumber shifts at B3LYP level are found to be inconsistent among the various dimers. Experimental evidence for the cyclic nature of alcohol tetramers is presented. A microscopic explanation for the positive deviations from Raoult's law in alcohol-ether mixtures is given. Ethers are shown to be useful as hydrogen-bonded ring strain detectors and as hydrogen bonded chain termini.