Electronic and Molecular Structure of Simple 3,3'-Bicyclopropenyls. Photoelectron Spectroscopy and Model Calculations

Article abstract of DOI:10.1002/hlca.19820650329

The electronic and molecular structure of 3,3'-bicyclopropenyl (1) and its alkyl derivatives 3,3'-dimethyl-3,3'-bicyclopropenyl (2), dispiro<2.0.2.3>nona-1,5-diene (3), dispiro<2.0.2.4>deca-1,5-diene (4), dispiro<2.0.2.5>undeca-1,5-diene (5), and dispiro<2.0.2.6>dodeca-1,5-diene (6) are studied by means of photoelectron spectroscopy and model calculations. 'Through-bond' effects in model compound 1 are analyzed in detail, illustrating a general difficulty with NDO models.Low-energy photoelectron bands of 2-6 can be assigned to ejection of electrons from cyclopropenyl ?- and Walsh-orbitals.Strong 'through-bond' coupling leads to splitting of the ?-bands in the range 1.0-1.5 eV, while the strongly conformation-dependent splitting of the Walsh-bands allows conclusions concerning the preferred torsional angles.The preference of gauche-conformation is predicted for 2 in the gas phase.