The potential energy surface for the solvent-free thioacetate hydrolysis reaction has been characterized by high level ab initio calculations of B3LYP/6-31++G(d,p). These calculations reveal that the approach of an OH ion leads to the formation of ion-molecule complex. The MS1 species with the hydroxide ion bound to acetyl and alkyl sides of thioacetate by C-H-O interactions. There are two reaction pathways to generate ethylthio anion and acetic acid products. One of the pathways reacts to Ethylthio anion, ketene and water complex intermediate structure, and the other reaction pathway leads to a famous intermediate structure, tetrahedral structure. We compared all the energies with other calculation theory to obtain the best theory for our study. Quantum calculations also predict that the transition states and intermediate structures for s-proply thioacetate and s-isoproply thioacetate.

(1) Lowry, T. H. r., K. S. Mechanism and Theory in Organic Chemistry, third edition ed.; Harper and Row: New York, 1987.
(2) McMurry, J. Organic chemistry : a biological approach; Thomson Brooks/Cole: Belmont CA., 2007.
(3) Li, P.; Zhao, K.; Deng, S. X.; Landry, D. W. Helv. Chim. Acta 1999, 82, 85.
(4) Bowden, K.; Battah, S. J. Chem. Soc.-Perkin Trans. 2 1998, 1603.
(5) Zhan, C. G.; Landry, D. W.; Ornstein, R. L. J. Am. Chem. Soc. 2000, 122, 2621.
(6) Sherer, E. C.; Yang, G.; Turner, G. M.; Shields, G. C.; Landry, D. W. J. Phys. Chem. A 1997, 101, 8526.
(7) Zhan, C. G.; Landry, D. W.; Ornstein, R. L. J. Am. Chem. Soc. 2000, 122, 1522.
(8) Williams, A. Enzyme mechanismsBurlington: London.
(9) Jencks, W. P. Catalysis in chemistry and enzymology; Dover.: New York
(10) Bakowies, D.; Kollman, P. A. J. Am. Chem. Soc. 1999, 121, 5712.
(11) Turner, G. M.; Sherer, E. C.; Shields, G. C. “A COMPUTATIONALLY EFFICIENT PROCEDURE FOR MODELING THE FIRST STEP IN THE ALKALINE-HYDROLYSIS OF ESTERS”, 1995.
(12) Sherer, E. C.; Turner, G. M.; Shields, G. C. “INVESTIGATION OF THE POTENTIAL-ENERGY SURFACE FOR THE FIRST STEP IN THE ALKALINE-HYDROLYSIS OF METHYL ACETATE”, 1995.
(13) Haeffner, F.; Hu, C. H.; Brinck, T.; Norin, T. Theochem-J. Mol. Struct. 1999, 459, 85.
(14) Stein, R. L.; Strimpler, A. M.; Hori, H.; Powers, J. C. Biochemistry 1987, 26, 1301.
(15) Stein, R. L.; Strimpler, A. M.; Hori, H.; Powers, J. C. Biochemistry 1987, 26, 1305.
(16) Vencill, C. F.; Rasnick, D.; Crumley, K. V.; Nishino, N.; Powers, J. C. Biochemistry 1985, 24, 3149.
(17) Weingarten, H.; Martin, R.; Feder, J. Biochemistry 1985, 24, 6730.
(18) Ye, Q. Z.; Johnson, L. L.; Hupe, D. J.; Baragi, V. Biochemistry 1992, 31, 11231.
(19) Douglas, K. T. Accounts Chem. Res. 1986, 19, 186.
(20) Staunton, J.; Weissman, K. J. Nat. Prod. Rep. 2001, 18, 380.
(21) Wong, B. J.; Gerlt, J. A. J. Am. Chem. Soc. 2003, 125, 12076.
(22) Benning, M. M.; Taylor, K. L.; Liu, R. Q.; Yang, G.; Xiang, H.; Wesenberg, G.; DunawayMariano, D.; Holden, H. M. Biochemistry 1996, 35, 8103.
(23) Jones, G. I. L.; Lister, D. G.; Owen, N. L.; Gerry, M. C. L.; Palmieri, P. J. Mol. Spectrosc. 1976, 60, 348.
(24) True, N. S.; Bohn, R. K. J. Am. Chem. Soc. 1976, 98, 1188.
(25) True, N. S.; Silvia, C. J.; Bohn, R. K. J. Phys. Chem. 1981, 85, 1132.
(26) Deerfield, D. W.; Pedersen, L. G. Theochem-J. Mol. Struct. 1995, 358, 99.
(27) Romano, R. M.; Della Vedova, C. O.; Downs, A. J. J. Phys. Chem. A 2002, 106, 7235.
(28) R. A., v. S., Matthew Neurock Molecular Heterogeneous Catalysis: A Conceptual and Computational Approcah; Wiley-VCH, 2006.
(29) Hammer, B.; Norskov, J. K. Theoretical surface science and catalysis - Calculations and concepts. In Advances in Catalysis, Vol 45; Academic Press Inc: San Diego, 2000; Vol. 45; pp 71.
(30) Lambert, R. M. P., G. Chemisorption and Reactivity on Supported Clusters and Thin Films; Kluwer, 1997.
(31) March, N. H., Lundqvist, S. Theory of the Inhomogeneous Electron Gas; Plenum Press, 1983.
(32) Slater, J. C. Quantum Theory of Molecular and Solids Vol 4 : The Self-Consistent Field for Molecular and Solids; McGraw-Hill: New York, 1974.
(33) Becke, A. D. Phys. Rev. A 1988, 38, 3098.
(34) Lee, C. T.; Yang, W. T.; Parr, R. G. Phys. Rev. B 1988, 37, 785.
(35) Miehlich, B.; Savin, A.; Stoll, H.; Preuss, H. Chem. Phys. Lett. 1989, 157, 200.
(36) Becke, A. D. J. Chem. Phys. 1993, 98, 5648.
(37) Foresman, J. B. exploring chemistry with electronic structure methods:a guide to using Gaussian; Gaussian, 1993.
(38) Guan, J. G.; Duffy, P.; Carter, J. T.; Chong, D. P.; Casida, K. C.; Casida, M. E.; Wrinn, M. J. Chem. Phys. 1993, 98, 4753.
(39) Chen, X.; Brauman, J. I. J. Phys. Chem. A 2005, 109, 8553.
(40) NIST webbook http://webbook.nist.gov/chemistry/
(41) Jorgensen, W. L.; Blake, J. F.; Madura, J. D.; Wierschke, S. D. Acs Symposium Series 1987, 353, 200.
(42) Pranata, J. J. Phys. Chem. 1994, 98, 1180.