Position-Specific C Fractionation during Liquid-Vapor Transition Correlated to the Strength of Intermolecular Interaction in the Liquid Phase.

The relationship between the strength of the intermolecular interaction in liquid and the position-specific C fractionation observed during distillation was investigated. A range of molecules showing different intermolecular interactions in terms of mode and intensity were incorporated in the study. Although it had previously been suggested that during evaporation the diffusive C isotope effect in the thin liquid layer interfaced with vapor is not position-specific, herein we show that this is not the case. In particular, the position-specific effect was demonstrated for a series of alcohols. Our hypothesis is that intermolecular interactions in the liquid phase are the source of position-specific C fractionation observed on the molecule. A clear trend is observed between the C isotope effect of the carbon bearing the heteroatom of chemical function and the relative permittivity, the solvent hydrogen bond acidity, and the solvent hydrogen bond basicity, while only a weak trend was observed when using the C content of the whole molecule. Furthermore, two families of products appeared when using the hydrogen bond acidity parameter for the correlation by distinguishing H-acceptor and H-donor molecules from those H-acceptors only. This strongly reinforces the hypothesis of an important role of the C positioned close to the interaction center.