Theoretical study on structure, conformation, stability and electronic transition of C4 and C5 anions of ascorbic acid stereoisomers

The structures, stabilities, conformational analysis and electronic transitions of l-ascorbic acid anions (four stereoisomers) were studied theoretically. These anions are produced from the de-protonation of C4–H and C5–H sites of l-ascorbic acid stereoisomers. The geometries of these anions were fully optimized in gas phase and aqueous phase in order to determine their relative stabilities. It was observed that the de-protonation at C5 site of two stereoisomers leads to the ring opening in both phases. Isomerization of the l-form to one of the d-form was observed during the optimization of the anions at C5. Conformational analysis (potential energy surface scan) of the opened ring anions was performed in search of energy minima and/or maxima. The absorption electronic transitions of the anions in the UV region were calculated using Time-Dependent Density Functional Theory (TD-DFT).