Is hydrogen bonding the reason for differences in vapour pressure and vaporisation energetics of optically active and racemic compounds?

Abstract

This work is a contribution to understanding of the thermodynamic properties of chiral compounds at the molecular level. The absolute vapour pressures of (RS)-2-amino-1-butanol, (S)-2-amino-1-butanol, (R)-2-amino-1-butanol, S-ethyl-lactate, and (RS)-1-methoxy-2-propylamine were measured by the transpiration method. The standard molar vaporisation enthalpies of these compounds were derived from vapour pressure–temperature dependences. The differences between vapour pressures and vaporisation enthalpies of racemates and enantiomerically pure isomers have been demonstrated and discussed. It was hypothesized that the intramolecular hydrogen bonds of the studied species in the gas phase are the reason for the observed differences.