Abstract:
Quantum-chemical modeling of intermolecular proton exchange in dimers of aminoacetic acid was carried
out using an unempirical unrestricted Hartree-Fock method using the 3–21G basis set. Three main structural
isomers of dimeric molecules of aminoacetic acid have been quantum-chemically identified. For these isomers,
the search for the structure of the transition state of the proton exchange reaction was carried out using
the quadratic synchronous transit QST2 (Quadratic Synchronous Transit Approach) procedure. The symmetrical
structure of the transition state for the dimer of aminoacetic acid is noted, in the formation of hydrogen
bonds of which two carboxyl functional groups are involved. The kinetics and mechanism of intermolecular
migration of a proton in the dimer of aminoacetic acid have been studied using the internal IRC (Intrinsic Reaction
Coordinate method) method. Curves are obtained for the dependence of the total energy of the reaction
system under consideration on the internal coordinate of the reaction. The activation energy of proton exchange
in dimers of aminoacetic acid is estimated as the difference in the total energies of the transition and
initial states of the reaction system. The minimum value of the activation energy (26 kJ/mol in the forward direction
and 34 kJ/mol in the reverse direction) was obtained for the intermolecular proton exchange reaction
in the dimer of aminoacetic acid, in the formation of the hydrogen bonds of which two carboxyl functional
groups are involved. The maximum value of the activation energy (244 kJ/mol in the forward direction and
236 kJ/mol in the reverse direction) was obtained for the intermolecular proton exchange reaction in the dimer
of aminoacetic acid, in the formation of hydrogen bonds of which two amino groups are involved.
