A grazing incidence x-ray diffraction study of CH3(CH2)(9)SH self-assembled on the (111) surface of gold revealed a disulfide head group structure, which provides a context in which to understand the structure and self-assembly process of this widely studied system. The structure consists of a nearly hexagonal two-dimensional arrangement of the hydrocarbon chains with a dimerization of the sulfur head groups (accommodated through a gauche bond), resulting in a S-S spacing of 2.2 angstroms. These results demonstrate the importance of internal molecular degrees of freedom in the templating of "soft" organic materials on inorganic substrates.