A simple technique for vibrational spectroscopy of metal/monolayer/silicon structures is applied to study the interaction of Au, Al, and Ti with alkane monolayers, either assembled onto thin oxides or directly attached to Si. The results are correlated with current-voltage and capacitance-voltage measurements. Alkane films on oxides are found to be robust with respect to the deposition of An and Al and are partially consumed during the deposition of Ti. In contrast, alkoxy films directly attached to H-terminated Si via an ether linkage are displaced by all three metals. The vibrational data are positively correlated with the electrical data to establish an improved understanding of the interactions at the buried metal/monolayer interface. The results demonstrate extreme sensitivity of the monolayer/metal reactivity to the nature of the film/substrate bonding.