Quantum chemistry calculations of phosphorous and methylphosphorous acids in dimethylformamide
Studies of solutions is one of the major tasks of modern physical chemistry as the understanding of processes occurring in them is necessary for a successful decision of many scientific and practical problems. To research the character of intermolecular interactions in solutions requires the establishment of initial molecules and complexes structure. Therefore, quantum chemistry methods of calculations appear rather suitable to decide such problems.
Proton acids solutions (phosphorous H3PO3 and methylphosphorous CH3H2PO3 acids) in organic solvents with basic properties are of special interest for studies since the formation of both hydrogen-bonded molecular complexes and ionic pairs capable of dissociating are quite possible in similar systems. DMFA was revealed to be one of such solvents.
Knowledge on structural and energy characteristics of investigated systems allows developing the theory of acid-base interactions involving weak acids. Moreover, it helps to form a clear view of intermolecular interactions mechanisms and proton transfer in non-aqueous environment.
Solutions of weak proton acids in DMFA can be used to obtain proton- conducting electrolytes as strong acids destroy DMFA. Furthermore, proton- conducting electrolytes are, in turn, used in fuel cells. Therefore, it is possible to develop fuel cells with improved characteristics on the basis of new proton- conducting electrolytes.
The characteristics of the molecules and molecular complexes under study were calculated using Gaussian-09 package.
DFT/B3LYP method with basis 6-31+G (d) was used to optimize geometrical parameters of molecules and complexes.
Initial configurations of molecules were obtained with program GaussView, symmetry restrictions being not used by optimization. Every optimized structure corresponded to the global minimum on the potential energy hypersurface and had no negative frequencies in a spectrum. The hydrogen bonds were studied by natural bond orbital analysis.
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