Dimerization is a side reaction that occurs during the preparation of a Grignard reagent. Propose a mechanism that accounts for the formation of the dimer. In the reaction scheme, a compound reacts with Mg in THF. The compound is a line-angle ring with six vertices and a Br atom attached. The first product is a line-angle ring with six vertices and an MgBr group attached. The second product is a dimer containing two six-vertex ring bound to each other through a single bond. Draw all missing reactants and/or products in the appropriate boxes by placing atoms on the canvas and connecting them with bonds. Add charges where needed. Electron flow arrows should start on the electron(s) of an atom or a bond and should end on an atom, bond, or location where a new bond should be created.