An empirical correlation between stretching vibration redshift and hydrogen bond length

A correlation is found between the magnitude of the redshift (Δv = 20 to 2500 cm^-1 relative to the free molecule) of the stretching mode of H- bonded A-H groups in an A-H···B complex, and the length of the H-bond (r(H···B) = 0.28 to 0.12 nm). The correlation is based on both new spectral data for narrow decoupled H-bands in cold isotopically diluted carbohydrate crystals with known H-bond distances and on literature spectral and structural data from a total of 36 systems. Once established, additional data for H-bonded crystals (hydrates, acid salts of carboxylic acids) and for gas phase dimer systems also fit this correlation quite well. Hydrogen bond enthalpies in the range of -ΔH = 10-80 kJ mol^-1 correlate with the inverse third power of the H-bond length. Literature experimental data on -ΔH and r(H···B) of ten gas phase dimers confirm this relationship.