The highly selective covalent binding of pyrazine on Si(111)-7 x 7 has been investigated using high-resolution electron energy loss spectroscopy (HREELS), X-ray photoelectron spectroscopy (XPS), and density functional theory (DFT) calculations. HREELS results clearly suggest that covalently attached pyrazine retains the sp(2) electronic configuration for all four carbon atoms, indicating that the carbon atoms of the ring are not directly involved in the chemical binding with the surface. The vibrational results further reveal that the aromatic ring of pyrazine is transformed to an unconjugated cyclodiene structure, implying the participation of N atoms in surface binding. This is further confirmed by the binding energy of N Is shifting to 399.0 eV in chemically bonded pyrazine compared to the value of 400.6 eV for physisorbed molecules. These experimental results coupled with our theoretical DFT calculations strongly suggest the di-sigma binding of the two para nitrogen atoms of pyrazine with an adjacent adatom-rest-atom pair on Si (111)-7 x 7, forming a 1,4-N,N-dihydropyrazine-like structure.