The conformation of the hydrogen bonded complex cyclohexene oxide/HCl: A rotational study

Cyclohexene oxide and its hydrogen bonded complex cyclohexene oxide/HCl have been investigated using a molecular beam Fourier Transform microwave spectrometer. The spectra of the parent species of cyclohexene oxide and its 13C and 18O isotopomers have been measured in their natural abundances. This has allowed obtaining the substitution and effective structures of the monomer heavy atom skeleton. A fast mixing nozzle has been designed to generate the complex preventing the reaction between the components. Only the equatorial conformer of the complex has been detected and its 35Cl and 37Cl isotopic species have been measured in their natural abundances. From the spectroscopic data the hydrogen bond structural parameters were obtained assuming that the structures of the monomers do not change upon complexation. HCl lies in the COC bisecting plane forming a non-linear hydrogen bond to the equatorial non-bonding electron pair at oxygen. The geometries of the axial and equatorial conformers have been optimized at MP2/6-311CCG(d,p) level of theory predicting the equatorial conformer as the most stable one. The non-observation of the axial form is discussed. q 2005 Elsevier B.V. All rights reserved.