Theoretical investigation on the effect of additional hydrogen bonded network on the ground state double proton transfer of 2-aminopyrazine-H₂O compound

The ground state double proton transfer (GSDPT) process of 2-aminopyrazine (APz) complex bonded with one bridged water molecule was investigated in detail at the M06-2X/6-31G(d, p) level. The extra hydrogen bonded (H-bonded) network formed between APz and 1 ~ 3 extra water molecules was drawn into APz-H₂O complex to form APz-(H₂O)_n+m (n = 1, m = 1–3) complexes, and its effects on GSDPT process in APz-H₂O were explored systematically. Based on the analyses of structural parameters and correlation plots, we found that the GSDPT reaction occurred in a concerted but asynchronous protolysis or solvolysis pattern depending on the location and number of the extra water molecules. The energy barrier of GSDPT process was also affected by the location and number of the extra water molecules.