A THEORETICAL-STUDY ON THE DECOMPOSITION MECHANISM OF BETA-PROPIOLACTONE AND BETA-BUTYROLACTONE

The reaction mechanism associated with the decomposition of P-propiola ctone and P-butyrolactone in the gas phase to form carbon dioxide and ethylene or propene, respectively, has been theoretically characterize d by using analytical gradients at the B3LYP/6-31G*, B3LYP/6-31++G**, MP2/6-31G* and MP2/6-31++G** calculation levels, as well as by singl e point calculations at QCISD(T)/6-31++G*//MP2/6-31++G**. A detailed analysis of the results points out that the reaction pathway can be de scribed as an asynchronous concerted process. The geometrical paramete rs and the components of the transition vector are weakly dependent on the computational method. By applying transition state theory, a good agreement between theoretical and observed values for the rate coeffi cient points out the validity of the theoretical methods. (C) 1998 Els evier Science B.V. All rights reserved.