Intramolecular double proton transfer from 2-hydroxy-2-iminoacetic acid to 2-amino-2-oxoacetic acid.

The double intramolecular proton transfer process which transforms 2-hydroxy-2-iminoacetic acid into 2-amino-2-oxoacetic acid is analyzed. The MP2 and DFT calculations were performed for different tautomers and conformers of these species. Pople style (6-311++G(d,p), 6-311++G(3df,3pd)) and Dunning type (aug-cc-pVTZ) basis sets were applied. O-H...O, N-H...O, and O-H...N intramolecular hydrogen bonds were also analyzed with the use of Quantum Theory of "Atoms in Molecules" (QTAIM) as well as Natural Bond Orbitals (NBO) method. Different criteria of the hydrogen bonding existence were applied here for intramolecular interactions. It was found that some of N-H...O hydrogen bonds may be treated as blue-shifting ones.