Conformation and stability of the hydrogen-bonded complex 6-oxabicyclo[3.1.0]hexane center dot center dot center dot HCl

The hydrogen-bonded complex between 6-oxabicyclo[3.1.0]hexane and hydrogen chloride was investigated by microwave spectroscopy in a super sonic jet. A dual flow pulsed valve was used to preclude chemical reaction between the monomers. Only the equatorial conformer was observed and the spectra of thr ee isotopomers, (C5H8O, (HCl)-Cl-35), (C5H8O, (HCl)-Cl-37) and (C5H8O, (DCl )-Cl-35), were measured. The derived structure of the complex has C-s symme try with the hydrogen chloride pointing to the domain of the equatorial lon e pair of electrons at the oxygen atom. The three atoms involved in the hyd rogen bond adopt a bent arrangement with a O ... H distance of 1.77(4)Angst rom, a (O ... H-Cl) angle of 115(4)degrees, and a deviation of 15.4(14)degr ees of the hydrogen bond from collinearity. In agreement with the ex perime ntal results, ab initio calculations predict the equatorial form to be the most stable one.