Solvent effect on proton transfer in the complexes of N,N-dimethylformamide with sulfuric and phosphoric acid: A DFT investigation

• An ab initio study of the proton transfer reaction is performed.
• The gas phase PES has two potential wells only for (H2SO4)2–DMF.
• In the DMF the proton transfer occurs for all complexes.
• The solvent effect favors a formation of ionic pairs.

Ab initio quantum-chemical calculations of structure and energies of the complexes of N,N-dimethylformamide (DMF) with sulfuric (H2SO4) and phosphoric (H3PO4) acids have been carried out. It has been found that the hydrogen bond between H2SO4 and DMF molecules is a little shorter and stronger than that between H3PO4 and DMF. The H-bond strength is different both in acid–acid and (acid)n–DMF complexes for n = 1, 2. The polar solvent effect is taken into account by using the CPCM approach. The differences of geometric parameters of the H-bonds in the gas phase and DMF are analyzed. The potential energy surface (PES) of the proton transfer reaction in acid–DMF and (acid)2–DMF complexes was calculated. The calculations have shown that the gas phase PES has a single distinct minimum (with the exception of the (H2SO4)2–DMF). In DMF, the proton transfer reaction takes place in all complexes, if OACID … ODMF distance is constrained. The solvent effect favors a proton transfer from sulfuric acid to oxygen atom of DMF molecule and formation of stable ionic pairs.

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