An empirical correlation between stretching vibration redshift and hydrogen bond length
A correlation is found between the magnitude of the redshift (Δν=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 (rH···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 rH···B of ten gas phase dimers confirm this relationship.