Lignin and naphthalene sulfonate plasticizers are organic polymers. Lignin, naphthalene, and melamine sulfonate superplasticisers are organic polymers. Commercially used creosote is often treated to extract the carbolic acid, naphthalene, or anthracene content. Further loss of hydrogen gives "fused" aromatic hydrocarbons, such as naphthalene, anthracene, phenanthrene, and pyrene. Examples are naphthalene, anthracene, and phenanthrene. Szwarc showed that electron transfer occurred from radical anion of naphthalene to styrene. Naphthalene and its alkyl homologs are the major constituents of creosote. For prochiral arenes (naphthalene, toluene, benzoates, benzopyrene), the epoxides are often obtained in high enantioselectivity. Fulvalene is an unstable isomer of the more common benzenoid aromatic compounds naphthalene and azulene. Others are dimers of naphthalene derivatives such as 1,1'-bi-2-naphthol. Tetralin is produced by the catalytic hydrogenation of naphthalene. It is a partially hydrogenated derivative of naphthalene. It forms white crystals that exhibit a characteristic, aromatic odor similar to that of naphthalene. Chronic exposure to naphthalene vapors is reported to also cause cataracts and retinal hemorrhage. Naphthoquinone is a class of organic compounds structurally related to naphthalene.