High pressure study on molecular conformational equilibria of n-pentane

The n-pentane molecule has the basic conformations, TT, TG, and GG. It is important for understanding the conformational behavior of chain molecules. We have studied the effect of pressure on the conformations of n-pentane in the condensed phase by using high pressure infrared spectroscopy with a diamond anvil cell up to 28.9 kbar. Compression of liquid n-pentane increases the concentration of the more globular conformers, while the TT conformer only exists as a high pressure solid. The volume changes for TT to TG, TG to GG, and TT to GG forms are −1.0±0.2, −1.1±0.3, and −2.1±0.3 cm3/mol, at 20 °C, respectively. The conformational volume changes in liquid n-alkanes are discussed in terms of the solvent-excluded volume.