UV photoelectron and ab initio study of intramolecular interactions in alpha-diethoxyphosphoryl carbonyl derivatives

Information on the geometric and electronic structures of alpha -diethoxyph osphoryl carbonyl derivatives, (RO)(2)P(O)CH2C(O)X, (1-5, X = CH3 1, CH3CH2 O 2, CH3CH2S 3, C6H5 4, (CH3CH2)(2)N 5), is obtained by W photoelectron spe ctroscopy and ab initio calculations. At the HF level, the CH2-P bond is ga uche to the carbonyl group except in 5. However, at the DFT and MP2 levels, the gauche conformation prevails for all the derivatives, in agreement wit h the spectroscopic data. This conformation is dictated by the interplay of the electronic interactions between the XC(O) and (RO),P(O) groups with tw o short contacts between pairs of oppositely charged atoms. The negatively charged carbonyl oxygen and one of the oxygen atoms bonded to phosphorus li e at distances shorter than (or close to) the sum of the corresponding van der Waals radii from the positively charged phosphorus and carbonyl carbon atom, respectively. The presence of through-space interactions in the groun d and ionised states is confirmed by eigenvector analysis and by the shifts in the MO energies with respect to those of reference compounds. In the gr ound state the non-bonded interactions are weaker than the corresponding in teractions in beta -carbonyl sulphones, RSO(2)CH2(C)(O)X, because of the le ss suitable geometry of the PO3 group, with respect to the SO2R group, for interaction with the P-carbonyl group. In the ionised state, however, the n egative charge on the oxygens of the phosphoryl group has a greater capacit y to relax toward the ionised XC(O) group thus reducing the ionisation ener gy values. (C) 2001 Elsevier Science B.V. All rights reserved.