A DFT study of the properties of substituted pyrrolidines and phospholanes in gas and in aqueous phase

Properties of nitrogen-containing organic molecules and their phosphorous analogs are studied theoretically both in gas phase and in aqueous phase with the use of density functional calculations. In the aqueous phase calculations, both a pure continuum (PCM) and a supermolecular/continuum model was used. Particular emphasis is put on the changes of the properties due to the systematic replacement of nitrogen atoms by phosphorous atoms. The properties include the relative energies of different tautomers and isomers, their dipole moment, and their free energy of solvation. Both from gas phase and from pure PCM calculations, for the nitrogen-containing compounds the most stable structures are characterized by strong intramolecular hydrogen bonds formed with the nitrogen atoms and the hydrogen atoms located outside the ring. When replacing the nitrogen atoms by phosphorous atoms this formation of hydrogen bonds is strongly affected which, in turn, leads to changes in the relative energies of different iso- and tautomers. Intermolecular hydrogen bonds between the solute and (explicit) water molecules of the solvent are responsible for the stability in the supermolecular/continuum calculations, whereby stronger hydrogen bonds with the water molecules are formed for the nitrogen-containing molecules. (C) 2011 Elsevier B.V. All rights reserved.