ELECTRON-DIFFRACTION STUDY OF THE MOLECULAR-STRUCTURE OF O-CHLOROANISOLE USING A DYNAMIC NONPARAMETRIZED MODEL

The geometrical parameters of the o-chloroanisole molecule were determ ined by gas phase electron diffraction in terms of the dynamic model u sing vibrational spectroscopy data and quantum chemical calculations. A new approach based on Tikhonov's regularization method is used to ex plicitly define the internal rotation potential of the methoxy group. It was found that the nonparametric internal rotation potential has tw o minima one of which corresponds to the planar (phi = 0 degrees) and another to orthogonal (phi = 90 degrees) orientation of the O-CH3 bond relative to the plane of the benzene ring. The difference between the energies of Be orthogonal and planar conformers is 0.9-1.0 kcal/mole, and the height of rotation barriers at phi congruent to 65 degrees is 1.4-1.6 kcal/mole, which confirms the results of quantum chemical cal culations, indicating that the orthogonal conformer is present in subs tantial amounts (similar to 30%). The following basic geometrical para meters were found (r(a) in Angstrom angle(alpha) in deg, the error equ als 3 sigma): r(C-C)(ave) = 1.398(4); r(O-C-Ph) = 1.358(36); r(O-C-Me) = 1.426(21); r(C-Cl) = 1.733(4); r(C-H)(Ph) = 1.086(6); r(C-H)(Me) = 1.095(6); angle CCOCCl = 118.7(2.2); angle COCC = 119.9(2.5); angle CO CClC = 121.5(1.1); angle COC = 117.6(2.6); angle COCCl = 119.1(2.1); a ngle CCO = 124.7(1.2). The results ate compared with the data for rela ted compounds. Stereochemical features of o-anisoles that are responsi ble for the orthogonal conformer are discussed.