Amidine decomposition mechanism. A theoretical study

Abstract

The unimolecular decomposition of the most simple amidine (formamidine) was examined by means of ab initio molecular orbital calculations. The Hartree-Fock method in the linear combination of atomic orbitals approximation with the 4-31G basis set was used. A complete potential hypersurface was established and the stationary points representing the reactants (R), transition state (TS) and products (P) were located. An analysis of the results shows that formamidine decomposition is an asynchronous process. The TS can be described as a four-membered ring. Following these results we decided to investigate a more complex system (acetamidine) and to examine the relevance of different basis sets. For acetamidine decomposition the calculations were carried out using the 3-21G, 4-21G, 4-31G, 6-31G, 6-311G, 6-31Gs* and 6-31G ∗∗ basis sets and the stationary points R, P and TS were located. It was found that the 4-31G basis set reproduces well the results obtained with more sophisticated calculations of energies and other quantum chemical indices. The structure of the TS was found to be relatively independent of the basis set used.