Raman spectroscopy is a widely used analytical technique that utilizes light scattered by vibrations from atoms to provide researchers with a unique signal, or fingerprint, for a given molecule. It turns out that nanoscale Raman, usually cast in the form of surface-enhanced Raman spectroscopy (SERS), reveals signatures not only of the measured molecular species, but also of their immediate chemical environments, like molecule-metal interfaces in our case. Here, entirely based on the picture of the interface electron-phonon coupling, we develop a thorough understanding of the effect known as "chemical enhancement" in Raman spectroscopy, opening new possibilities for using nanoscale Raman in chemical analysis.