Interactions in 2,8,9‐trifunctional [3.3.3] propellanes

The He(I α ) photoelectron (PE) spectra and electronic spectra of the 2,8,9‐trifunctional [3.3.3]propellanes 3, 6, 8 , and 9 together with the corresponding 2‐mono‐ and 2,8‐difunctional species have been recorded. The PE investigations reveal a small split between the π bands in the PE spectra of 2 and 3 and the n‐lone pair bands in those of 7 and 9 . This is rationalized by assuming a small through‐space interaction among the functional groups. A considerable π‐n splitting is found in the case of 5, 6 , and 8 . This splitting is due to a fairly strong interaction of n and σ orbitals with the σ frame of the corresponding propellane. The first band of the electronic spectra of 6, 8 , and 9 is assigned to π* ← n transitions on the basis of CNDO/s‐CI calculations. These investigations suggest a small split among the lowest unoccupied π* orbitals.