Through-space interaction in non-conjugated acyclic dienes studied by photoelectron spectroscopy

The He (I) PE-spectra of the non-conjugated acyclic dienes 1 (n), n = 5, 6, 7, 8, 9 are reported. The π-level splitting in the molecules amounts respectively to 0·34, 0·46 (or 0·31), 0·41, 0·21 and 0·14 eV. Arguments based on the observed fine structure of the first two bands suggest there is no crossing of the π-levels, and EHT calculations on different conformations of 1 (5) and 1 (6), as well as comparisons with other available data, indicate a through-space dominated interaction throughout the series 1 (n).