Polarization modulation Fourier transform infrared reflection absorption spectroscopy (PM-FTIRRAS) has been utilized to study the in situ structure of octadecanethiol when adsorbed to gold electrode surfaces and with the application of potential to the substrate. It is found that applied potential has little effect upon the spectrum of the monolayer in the presence of D2O solutions containing 0.10 M NaClO4. The presence of an acetonitrile solution contacting the monolayer leads to small changes in the infrared spectrum relative to that seen in D2O solutions, suggestive of some small disordering of the monolayer caused by the presence of the acetonitrile. With the application of potential, however, the infrared peak positions for the methyl and methylene modes return to the positions observed in the pseudo-crystalline ex situ spectrum, suggesting that the applied potential has an organizing effect upon the monolayer in the acetonitrile solutions.