Electronic interactions in 2-(ethylsulphonyl) ketones studied by ultraviolet photoelectron spectroscopy

The bands present in the low ionization energy region (EI <= 12 eV) of the (He I and He II) photoelectron spectra of some aromatic (R = NO2C6H4, 4; C6H5, 5; MeOC6H4, 6; n= 1) and aliphatic (R = Me, and n= 1, 2; or 2, 3) ethylsulphonyl ketones, RC(O)(CH2)nSO2Et, have been assigned to the corresponding molecular orbitals by comparison with the assignments reported for simpler related molecules. The comparison has been assisted by the determination of the geometric structure of 6. (by X-ray diffraction) and of the model compounds HC(O)CH2SO2H and p-C6H4C(O)CH2SO2CH3(by semiempirical calculations). Oppositely charged atoms of the carbonyl and ethanesulphonyl groups are separated by distances shorter than the sum of the van der Waals radii, allowing crossed charge-transfer interactions. Low symmetry allows a deep through-space and through-bond mixing among the various group orbitals, as indicated by experimental Ei values and theoretical calculations.