Results from inelastic electron tunneling spectroscopy (IETS), IR transmission, and multiple reflection-absorption infrared spectroscopy are presented in a comparison of the adsorption of monolayers of vinylphosphonic acid (VPA) and vinyltriethoxysilane (VTES) on oxidized aluminum. Spectra obtained from VPA suggest that adsorption occurs via a condensation reaction that forms a resonance structure involving deprotonated hydroxyl oxygen atoms and the phosphoryl oxygen. A symmetric tridendate structure is proposed and discussed for the adsorbed state of VPA. For adsorbed VTES, these results support a previously proposed reaction involving condensation and formation of siloxanes at the oxide surface. The relative intensities of the bands associated with the vinyl group are similar for both compounds, suggesting that the organofunctional groups are oriented on the surface in the same way and, in the case of lETS, that the Pb top electrode has little effect on band position.