Intermolecular Hydrogen Bonding of Enantiomers of Pantolactone Studied by Infrared and 1H-NMR Spectroscopy

Intermolecular associations of the enantiomers of pantolactone in carbon tetrachloride solution have been studied by infrared and 1H-NMR spectroscopic methods. The spectroscopic data have been analyzed by the least squares method to obtain the association constants and thermodynamic parameters. It was found that pantolactone takes a cyclic dimer structure by dint of hydrogen bonding. The association constant for homochiral dimerization was obtained to be 8.9 mol−1 dm3 at 26°C and the enthalpy and entropy changes were −35 kJ mol−1 and −97 J K−1 mol−1, respectively. The association constant for heterochiral dimerization is just twice as large as that for homochiral dimerization, that is, no selective association exists between enantiomers.