Structures and Conformational Analysis of Monosubstituted Cyclopropanes of the Type: c-Pr-XY3 and c-Pr-CH2-XY3 (X = Si, Ge; Y = H, F, Cl)

The molecular structures of various cyclopropanes of the type C3 H5-XY3 and C3 H5 -CH2 –XY3 have been investigated by means of electron diffraction, vibrational spectroscopy and ab initio computations. Interesting systematical structural changes have been observed as a result of the variation of the substituent group XY3. Among these are the disparity of the ring C-C bond lengths, the shortening of the Cring -X bond and the increase of the positive tilt of the XY3 group upon XH3/XF3 substitution. A dynamical scheme for the treatment of the torsional vibration of the SiF3 group as a large amplitude motion has been used. The potential barrier for the XY3 moiety was determined. A conformational analysis of the C3H5-CH2-SiH3 and its fluorinated counterpart with respect to the Cring -CH2 and the CH2-Si axis has been performed. Whereas only the gauche conformer in the former compound is stable, the latter one exists in two stable forms, the cis, 55%(10), and the gauche, 45%(10). Vibrational mean square amplitudes and harmonic corrections for converting the ra into rα distances were calculated from ab initio force fields.