Short intramolecular hydrogen bonds: Proton-NMR and IR spectra as a function of O - - - O distance

Infrared absorption frequencies and ¹H NMR chemical shifts have been measured as a function of O - - - O distances in compounds with short intramolecular hydrogen bonds. Two types of molecules were investigated, those with intramolecular O-H-O bonds within chelate or constrained systems having no degree of rotational freedom along the O-H-O axis, and molecules possessing symmetry-restricted or unrestricted hydrogen bonds with complete rotational freedom along the O - - H - - O axis. While electronic factors are most important for the nature of the short hydrogen bond in the latter compounds (such as dimeric hydronium ions of pyridine-N-oxides), steric constraints play a dominant role for the former (such as metal glyoximates). ¹H MMR chemical shifts δ(O-H-O) (ppm) and IR absorption frequencies v(O-H-O) (cm^-1) as a function of the O - - - O distance are discussed.