Comment on “Local, solvation pressures and conformational changes in ethylenediamine aqueous solutions probed using Raman spectroscopy” by M. Cáceres, A. Lobato, N. J. Mendoza, L. J. Bonales and V. G. Baonza, Phys. Chem. Chem. Phys., 2016, 18, 26192

Abstract

Liquid ethylenediamine contains both trans and gauche conformers, but there are conflicting claims in the literature that the relative abundance of gauche conformers is either completely quenched (J. Mol. Struct., 1999, 482, 639–646) or enhanced (Phys. Chem. Chem. Phys., 2016, 18, 26192–26198) in 1 M aqueous solutions. Density-functional-theory spectra predictions are employed here to resolve the conflict. In both the 1999 and 2016 reports, the effects seen were misinterpreted, and are instead due to loss of direct amine–amine H-bond interaction upon dilution, which appears to be complete at ∼0.66 mole fraction of water. Both trans and gauche conformers of ethylenediamine are concluded to be present, in both liquid and aqueous phases, with as yet no solid evidence for a shift in conformer ratio.