Unraveling the oxidation of graphitic lattice is of great interest for atomic-scale lattice manipulation. Herein, we build epoxy cluster, atom by atom, using Van der Waals' density-functional theory aided by Clar's aromatic it-sextet rule. We predict the formation of cyclic epoxy trimers and its linear chains propagating along the armchair direction of the lattice to minimize the system's energy. Using lowtemperature scanning tunneling microscopy on oxidized graphitic lattice, we identify linear chains as bright features that have a threefold symmetry, and which exclusively run along the armchair direction of the lattice confirming the theoretical predictions.