The reaction of acenaphthylene with the Si(001) surface has been investigated as a model system for understanding how complex pi-systems interact with a pi-bonded semiconductor surface. Scanning tunneling microscopy (STM) reveals that bonding occurs over a dimer row for more than 90% of the adsorbed molecules. Fourier transform infrared spectroscopy (FTIR), using isotopically labeled derivatives of acenaphthylene, shows that bonding occurs through the 1,2-alkene, leaving the aromatic portion of the molecule mostly unperturbed. The reaction between acenaphthylene and Si(001) represents a potential method for coupling extended pi-electron systems with group IV semiconductor surfaces.