Molecular orbital calculations on the P-S bond cleavage step in the hydroperoxidolysis of nerve agent VX

Eric V. Patterson, Christopher J. Cramer

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26 Scopus citations

Abstract

The P-S bond cleavage process in the hydroperoxidolysis of a model system for the nerve agent VX was studied using ab initio and semiempirical molecular orbital methods. Aqueous solvation effects were included through single-point calculations using the semiempirical SM5.2PD/A continuum solvation model and geometries optimized at the HF/MIDI! level of theory. The predominant pathway for P-S bond cleavage involves pseudorotation of a low-energy trigonal bipyramidal intermediate followed by apical ligand ejection. In aqueous solution, the free energy barriers for these processes are found to be 14.3 and 4.6 kcal mol-1, respectively, with electronic energies calculated at the MP2/cc-pVDZ//HF/MIDI! level of theory. By comparison with another continuum model of solvation (PCM), it is concluded that the SM5.2PD/A model performs well even for hypervalent phosphorus species, in spite of not having included any such molecules in the model's parameterization set.

Original languageEnglish (US)
Pages (from-to)232-240
Number of pages9
JournalJournal of Physical Organic Chemistry
Volume11
Issue number4
DOIs
StatePublished - Apr 1998

Keywords

  • Hydroperoxidolysis
  • Molecular orbital calculations
  • Nerve agent VX
  • P-S bond cleavage

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