REACTIONS OF ORGANIC MONOLAYERS ON CARBON SURFACES OBSERVED WITH UNENHANCED RAMAN-SPECTROSCOPY

High sensitivity surface Raman spectroscopy was used to acquire spectra from monolayers of nitrophenyl groups covalently bonded to glassy carbon (GC) and ordered graphite. 4-Nitrophenyl radical was generated by electroreduction of 4-nitrophenyl diazonium ion in acetonitrile, then the radical covalently bonded to the carbon surface. Raman spectroscopy with a 488 nm laser and a CCD spectrograph revealed spectral features characteristic of the nitrophenyl group. Voltammetry, XPS, and Raman spectroscopic data established that the surface coverage was 6.5 x 10(-10) mol/cm(2) on glassy carbon and 1.6 x 10(-10) mol/cm(2) on the basal plane of highly ordered pyrolytic graphite (HOPG). Electrochemical reduction of the nitrophenyl surface yielded significant spectral changes, perhaps due to formation of an amine. The similarity of the Raman results for modified HOPG and GC surface indicates that the nitrophenyl radical is quite aggressive, apparently attacking both edge plane and basal plane sites.