Conformational studies have been carried out on the two different enantiomers of tabun at the density functional and second order Moller-Plesset perturbation levels of theory to generate low energy potential energy surfaces in the gas phase as well as in aqueous environment. The structures of the low energy conformers together with their molecular electrostatic potential surfaces have been compared with those of the non-aged acetylcholinesterase-tabun complex to locate the active conformer of this molecule. (c) 2006 Elsevier B.V. All rights reserved.