The epitaxial growth of ultrathin organic films (alkane thiolates) on single crystalline metal surfaces is investigated via low energy electron diffraction (LEED) with special emphasis on nonane [CH3(CH2)(8)SH] molecules, vacuum deposited on Au(111) surfaces. As a function of increasing coverage, the unit cells of nonane thiol can be described by c(21 x root 3) and p(5 x root 3), In between and without further change in coverage, the p(5 x root 3) is changed into a c(10 x 2 root 3)R30 degrees structure. The structural changes are interpreted as being due to a decrease of tilt angle of the molecules with respect to the surface normal, followed by a rotation of the molecules with respect to the C-C-C plane of the carbon chains.