The adsorption and reaction of aniline, phenol, methoxybenzene, benzonitrile, chlorobenzene, nitrosoben-zene, nitrobenzene, and benzaldehyde were studied on Ni(lll) groups to elucidate the role of substituent groups in adsorption and reaction of substituted benzenes. Temperature-programmed reaction (TPR) and reflection absorption infrared spectroscopy were used to characterize modes of bonding and reaction paths. The absorption bonds were also modeled by using the semiempirical intermediate neglect of differential overlap technique (INDO) with a 19 nickel atom cluster having the symmetry of the (111) surface. The nickel surface acted as an electron acceptor in electrophilic reactions with adsorbates. Chlorobenzene was found to adsorb flat, with the chlorine atom participating in the bond to the surface. With electron-withdrawing groups, the substituents were the site of chemical activity. The CN side group in benzonitrile rehybridized upon adsorption on Ni(lll), resulting in a bonding configuration in which the phenyl ring was tilted away from the surface. Benzaldehyde also apparently interacts mainly through the C=0 bond of the CHO side group. NO bonds were particularly reactive. Nitrosoben-zene and nitrobenzene bonded dissociatively through their side group, and NO bond scission was very facile. Electron-donating groups activated the benzene for electrophilic addition reactions. It is postulated that the amine substituent in aniline was activated by electrophilic attack by the surface leading to polymerization. The polyaniline was thermally very stable and did not decompose to above 700 K. Evidence for phenol polymerization was also found. In methoxybenzene, the bulky methyl side group hindered the polymerization, and the molecule decomposed. INDO calculations were found to be useful in identifying charge transfer during adsorption and in elucidating the reaction pathways.
All Science Journal Classification (ASJC) codes
- Materials Science(all)
- Condensed Matter Physics
- Surfaces and Interfaces