Furan is a cyclic flammable liquid compound C4H4O that is obtained from wood oils of pines or made synthetically and is used especially in organic synthesis. Furan is aromatic because a pair of lone pair electrons of the oxygen atom in its molecule forms a large π bond in the plane of the conjugated orbital, making a total of 6 electrons in the plane of the conjugated plane, conforming to the 4n+2 structure. Aromaticity makes furan have the property of easy substitution and difficult addition. The other lone pair of electrons in oxygen stretches out. The oxygen atom itself conforms to sp2 hybridization. Due to the presence of the aromatic ring, the chemical behavior of furan is not very similar to that of other unsaturated heterocycles. The oxygen in the aromatic ring has an electron-donating effect, so the electrophilic substitution reactivity of furan is stronger than that of benzene.