Unimolecular decomposition of the anionic form of N-chloro-alpha-glycine. A theoretical study

The molecular mechanism for the unimolecular decomposition of the anionic form of N-chloro-alpha-glycine in its singlet and triplet electronic states has been theoretically characterized by using analytical gradients and AM1 and PM3 semiempirical procedures as well as the ab initio RHF and UHF methods at 4-31G, 6-31G*, and 6-311+G* basis set levels. Correlation effects were included by using the perturbational approach at the MP2/6-31G* level. The global potential energy surfaces have been further studied, and the stationary points were localized and characterized. The geometry, electronic structure, and the transition vector associated with the transition structures have been analyzed. The dependence of these properties upon theoretical methods is analyzed and discussed. The topological analysis of the fundamental singlet and tripler PESs shows the existence of a quadratic flat region that plays a fundamental role in the description of the nature of the molecular mechanism. The decomposition process takes place in the singlet electronic state. The geometry and electronic structure for TSs in singlet and triplet states correspond to antiperiplanar conformations, possessing a productlike character. The unimolecular decomposition mechanism is a concerted and slightly asynchronous process.