Ion pairs of lithium salts based on three organic anions, namely Tf-, TFSI-, and TFSM-, have been studied by ab initio quantum-chemical methods. These calculations allowed us to draw the conformational energy diagram for TFSM- and TFSI-. Geometries and binding energies have been evaluated at the restricted Hartree−Fock (RHF) level using standard basis set (3-21+G* and 6-31+G*). For the reference Tf-−Li+ , electron correlation effects have been determined at the MP2 level. Wave function analyses have been performed by the natural bond orbital (NBO) method. Bidentate structures involving two oxygen atoms (one of each SO2 group in the TFSI-,Li+ and TFSM-,Li+ systems) are preferred. The affinities of these anions for the lithium cation are strong and lie in the range 120−145 kcal·mol-1, arising essentially from the electrostatic interaction. Charge transfer contributions are less important, only 14−17% of the electrostatic interaction.

We have performed a detailed study of the title reaction, which is the key step of one of the most realistic processes suggested for the prebiotic synthesis of amino acids. From a methodological point of view, our results confirm the reliability of the integrated computational tool formed by the B3LYP density functional model and the polarizable continuum model for the description of solvent effects. From a more chemical point of view, the reaction is quite unlikely in the gas phase due to the presence of significant reaction barriers, whereas the aqueous medium leads to a more feasible mechanism thanks to the preferential solvation of zwitterionic transition structures. Both specific and bulk solvent effects play a role in determining the overall mechanism.