Journal of Physical Chemistry A, Vol.114, No.50, 13189-13197, 2010
Theoretical Proton Affinity and Fluoride Affinity of Nerve Agent VX
Proton affinity and fluoride affinity of nerve agent VX at all of its possible sites were calculated at the RI-MP2/cc-pVTZ//B3LYP/6-31G* and RI-MP2/aug-cc-pVTZ//B3LYP/6-31+G* levels, respectively. The protonation leads to various unique structures, with H+ attached to oxygen, nitrogen, and sulfur atoms; among which the nitrogen site possesses the highest proton affinity of -Delta E similar to 251 kcal/mol, suggesting that this is likely to be the major product. In addition some H-2, CH4 dissociation as well as destruction channels have been found, among which the CH4 + [Et-O-P(=O)(Me)-S-(CH2)(2)-N+(iPr)=CHMe] product and the destruction product forming Et-O-P(=O)(Me)-SMe + CH2=N+(iPr)(2) are only 9 kcal/mol less stable than the most stable N-protonated product. For fluoridization, the S-P destruction channel to give Et-O-P(=O)(Me)(F) + [S-(CH2)(2)-N-(iPr)(2)](-) is energetically the most favorable, with a fluoride affinity of -Delta E similar to 44 kcal. Various F- ion-molecule complexes are also found, with the one having F- interacting with two hydrogen atoms in different alkyl groups to be only 9 kcal/mol higher than the above destruction product. These results suggest VX behaves quite differently from surrogate systems.