Spectroscopic studies of proton transfer in hydrogen bonding: adenine complexed to HCl

The H-bond interaction of the adenine with HCl is investigated using the combined matrix-isolation FT-IR and theoretical density functional theory. Theoretical calculations indicate that three closed complexes of the type III (proton transfer or ion pair H-bond), each containing two hydrogen bond, i.e., N1+–H⋯Cl−⋯H–NH; N3+–H⋯Cl−⋯H–N9 and N7+–H⋯Cl−⋯H–NH, have been obtained. The experimental spectra are consistent with this prediction.