Electronic and Molecular Structure of Simple Bicyclopropyls. Photoelectron Spectroscopy and Model Calculations

Article abstract of DOI:10.1021/jo00137a011

The electronic and molecular structure of bicyclopropyl (1), 1,1'-dimethylbicyclopropyl (2), dispiro<2.0.2.3>nonane (3), dispiro<2.0.2.4>decane (4), dispiro<2.0.2.5>undecane (5), dispiro<2.0.2.6>dodecane (6), dispiroheptane-3',1''-cyclopropane> (7), dispirooctane-3',1''-cyclopropane> (8), cis- and trans-tricyclo<5.1.0.0^2,4>octane (9 and 10), cis- and trans-tricyclo<6.1.0.0^2,4>nonane (11 and 12>, and trans-tricyclo<7.1.0.0^2,4>decane (13) have been investigated by means of photoelectron (PE) spectroscopy (2-6 and 11-13), model calculations, and empirical correlation procedures.Low-energy PE bands of 1-13 can be assigned to ejection of electrons from the bicyclopropyl Walsh orbital system and are conveniently discussed in terms of a simplified "Linear Combination of Walsh Orbitals" (LCWO) model, allowing tentative prediction of conformational features from the PE data.In the case of the mobile species 1 and 2, the PE spectra are best understood under the assumption that the observed maxima in the low-energy region correspond to the gauche conformer, implying that contributions from the trans conformer are either weak or broad and featureless.This assumption is at variance with previous interpretations but is supported by a consideration of torsional amplitudes and the results of LCWO and all-valence-electrons calculations.