A two-level model of an organic macromolecule has been put forward in order to analyze theoretically the interaction of dangling molecular orbitals of the organic macromolecule with quasi-free-standing and epitaxial graphene. The model initially contains a completely filled (HOMO) and empty (LOMO) levels. Within the framework of the standard adsorption approach, the interaction of these levels with quasi-free and epitaxial graphene was considered. Silicon carbide polytypes were considered as substrates. Our estimates showed that the maximum transition of electrons from dangling bonds to epitaxial graphene took place for the 3C-SiC substrate.