On the question of hydrogen bond proton transfer

A simple relation is found that connects the proton displacement value along the line of an H-bond X-H…Y at its formation with the proton transfer barrier to the acceptor Y. The fulfillment of the relation is verified by quantum-chemical calculations at the B3LYP/6-31+G(d, p) level of a series of H-bonded molecular complexes at different interatomic distances X…Y. With the aim to analyze the accuracy of this relation, calculations of model complexes were also performed with different basis sets. The effects of the basis set extension and electron correlation on the calculated values of the proton transfer barrier and the length of the X-H covalent bond in the molecular complex are considered. Using the suggested formalism for problems of proton transfer in H-bonded systems is discussed. A criterion of the barrierless transfer is introduced.