Theoretical studies on the all-anti zigzag geometries of perfluoro-n-alkyl chains

Theoretical investigations were conducted on the gas phase all-anti zigzag geometries of C~3~ through C~7~ perfluoro-n-alkanes and the perfluoro-n-octanoate anion using various semiempirical, density functional theory, and composite method approaches. The major theoretical methods are in agreement that the gas phase zigzag geometry of >=C~3~ perfluoro-n-alkyl chains is a transition state between the left and right handed helical/twisted global minima. For the C~3~ perfluoropropyl group, a slightly twisted (about 1 to 2 degree central F-C-C-F dihedral angle) near zigzag conformation exists as a global minimum, whereas helical global minima are obtained for C~4~ and longer perfluoroalkyl chains. The left to right handed helix inversion activation energy for C~4~ and C~5~ perfluoroalkyl groups is estimated at between 1 and 2 kcal/mol