Influence of proton transfer on the geometry of the donor and acceptor in NHN super(+) hydrogen bonds

The correlation between distances X-H and H-Y in hydrogen bonds has been studied extensively but it is difficult to determine experimentally individual changes in the internal structure of the molecules involved in the hydrogen bonds. In the present study the influence of proton transfer on the geometry of donors and acceptors in NHN super(+) hydrogen bonds has been investigated by theoretical calculations at the B3LYP/6-31++G** level of theory using the Gaussian03 system. The selected compounds provide examples of both inter- and intramolecular hydrogen bonds. Typically, the largest changes are in the bonds involving the closest neighbors to the NHN bridge atoms, but in certain cases the geometrical features of parts that are more remote from the bridge atoms are also affected, and can result in significant changes of the conformation of the molecules.