Molecular structure of tetravinylmethane from gas-phase electron diffraction

The molecular structure of tetravinylmethane has been investigated by gas-phase electron diffraction. Four C-C bonds may be axes of torsion in this molecule, hence a priori, an enormous number of conformers are possible. Preliminary analysis of the experimental radial distribution allowed the reduction of the number of conformations to be considered to four. Subsequent least-squares refinement indicated the presence of one conformational isomer only. This conformation is similar to that obtained by X-ray crystallography. The all-carbon frame of the molecule may be characterized by a carbon tetrahedron standing on three C=C legs out of one of the sides (2-3-4) of this tetrahedron, of approximately C(3) symmetry. The fourth C=C bond is positioned as if it were a handle of the tetrahedron, approximately eclipsing one of the C-C bonds. Some fragments of the carbon skeleton display further approximate local symmetries, such as a twofold axis of the C7-C3-C1-C5-C9 chain and a symmetry plane of the C8-C4-C1-C5-C9 chain. The following bond lengths (r(g)), bond angles, and dihedral angles characterize this structure: C-H 1.101 +/- 0.002 Angstrom; C=C 1.336 +/- 0.003 Angstrom; C-C 1.522 +/- 0.003 Angstrom; C-C=C 127.0 +/- 0.2 degrees; C=C-H 123.7 +/- 0.7 degrees; C-C-C 109.5 degrees (assumed); C-C-H 117.0 degrees (assumed); Z-C1-C2=C6 24.8 +/- 1.5 degrees; Z-C1-C3=C7 - 121.7 +/- 2.7; Z-C1-C4=C8 - 68.6 +/- 1.8 degrees; Z-C1-C5=C9 39.8 +/- 2.4 degrees, where C1 is the central carbon atom and Z is the bisector of the C2-C1-C3 angle. A torsional angle is zero in the eclipsed position. Any clockwise torsion, closest to us, out of the eclipsed position is positive. (C) 1998 Elsevier Science B.V.