Vitamin C is an essential component for organisms and is responsible for various functions in the human body. Its structure is in a way that suffering significant structural changes during storage. Despite extensive previous studies on degradation process of vitamin C, there are still facing many complexities and ambiguities. Herein, the stability of vitamin C in water at various thermal (room and 90 °C) and atmospheric (oxygen and argon) conditions were monitored by optical rotation changes as a function of time intervals. Results indicate that raising temperature and oxygen atmosphere increase the rate of degradation. The obtained reaction mixtures were analyzed by FT-IR, 1 H-NMR, and GC-MS techniques. Comparison of the obtained results of these analyses implies the formation of some similar degradation products in different applied conditions. In the theoretical studies section, the nature of inter- and intramolecular interactions of vitamin C were discussed. High content of hydroxyl group in vitamin C (VC) structure leads to a wide range of inter- and intramolecular interactions. The nature of intramolecular interactions within the various vitamin C conformers was studied in view of interacting quantum atom (IQA) approach. Complete IQA analysis of atomic and interatomic interaction energies indicated hydrogen bonds formation was responsible for the stability of most of the local minima in the potential energy surface. In these conformers, tandem participation of interactions was operating in a way of two- or three-centered (bifurcated) cooperative networks. To providing better understanding of the complex behavior of vitamin C in living systems, the intermolecular interactions of vitamin C with L-alanine (as the simplest chiral amino acid) were studied. The complexes are formed via two hydrogen bond interactions, which result a ring-like hydrogen bonded networks. The nature of intermolecular interactions was characterized in terms of natural bond orbital (NBO), natural energy decomposition analysis (NEDA), natural resonance theory analysis (NRT), and quantum theory of atoms in molecule analyses (QTAIM).
