Structural properties of perfluorinated linear alkanes : a 19F and 13C NMR study of perfluorononane

Liquid perfluorocarbons exhibit unique physical-chemical characteristics such as extraordinary stability, combined hydrophobia and lipophobia, low surface tension and a capacity to carry large quantities of gas. They have found widespread use in industry, medicine and biology even though the molecular origin of these properties is not fully understood. The objective of the present work was to elucidate the physical behavior of perfluorinated linear alkanes by investigating their intramolecular electronic environment using 13C and 19F NMR techniques in combination with theoretical calculations of molecular orbitals. Particular advantage was taken of 19F-19F through-space couplings, which led us to propose a molecular model in which delocalized p-electrons of the fluorines cover the entire surface of the molecule in two pairs of intertwined helices. Experimental data are presented for n-perfluorononane and supported by corresponding measurements with shorter and longer perfluorinated alkanes.