Direct chemical vapor deposition (CVD) of graphene on industrially preferred semiconductor (such as c-Si) or dielectric substrates is a desirable approach to incorporate graphene into electronic devices, thus preventing the commonly used transfer process of graphene films from Cu foils, which inevitably leads to residual contamination and mechanical defects. The CVD synthesis of graphene on Si substrates is realized using methane at high temperature (>900°C), although the low diffusivity of carbon species and the strong carbon solubility in Si lead to the unavoidable formation of SiC buffer layers, which severely hamper an efficient growth. Though several strategies have been adopted to overcome such limitations, few studies have focused on the use of aromatic hydrocarbons as possible carbon precursors. We recently reported on a DFT study of adsorption and most-likely decomposition paths of liquid aromatic hydrocarbons onto Cu(111) and showed that methyl dehydrogenation of toluene is the most favored one, leading to the abundant formation of adsorbed benzyl radicals onto Cu, as active species for graphene nucleation. Here, we report on early decomposition steps of toluene and possible recombination pathways of as-formed active species onto the c(4x2)-reconstructed Si(100) surface through density functional theory (DFT) calculations with van der Waals corrections (DFT-D3). Toluene molecules can chemisorb with several configurations onto the Si surface by addition reactions. We found the most stable configuration is the aromatic ring forming four sigma bonds with two adjacent Si dimers, having an adsorption energy of 1.39 …