Conformational Equilibria in Adducts of Alcohols with Ethers: The Rotational Spectrum of Ethylalcohol-Dimethylether

The rotational spectra of two conformers of the molecular complex ethylalcohol-dimethylether were measured with pulsed-jet Fourier transform microwave spectroscopy. Both trans and gauche conformations of ethylalcohol are preserved in the complex, originating two conformations with dimethylether as the proton accepting unit. A switch of the conformational stability of ethyl alcohol is observed upon complexation with dimethyl ether, with the gauche form becoming the global minimum. The investigation of the O-D deuterated species allowed observing quantitatively the Ubbelohde effect, which is the shrinkage of the O center dot center dot center dot O distance of about 6 m angstrom upon H -> D isotopic substitution of the hydroxylic hydrogen participating in the O-H center dot center dot center dot O hydrogen bond.