A density functional theory study of the conformational properties of 1,2-ethanediamine: protonation and solvent effects

The structures and the conformational energies of nonprotonated, monoproton ated and diprotonated 1,2-ethanediamine have been investigated through dens ity functional theory. The relative performance of local and gradient-corre cted functionals is discussed. The existence of hydrogen-bond formation has been determined with electron localisation function calculations. Proton a ffinities for nonprotonated and monoprotonated 1,2-ethanediamine have been calculated and are in agreement with experimental data. The influence of so lvation has been accounted for through the self-consistent isodensity polar isable continuum model. The results for the nonprotonated conformers show t hat solvation stabilises those conformers which have the lone pair in an an tiperiplanar conformation. Solvation of the monoprotonated conformer stabil ises significantly the "anti" conformation, which is unstable in the gas ph ase. For the di-protonated species, solvation stabilises slightly the gauch e conformer, which is unstable in the gas phase.