Retene, methyl isopropyl phenanthrene or 1-methyl-7-isopropyl phenanthrene, C₁₈H₁₈, is a polycyclic aromatic hydrocarbon present in the coal tar fraction, boiling above 36 °Celsius. It occurs naturally. It also occurs in the tars obtained by the distillation of resinous woods. It crystallizes in large plates, which melt at 98.5 °C and boil at 390 °C. It is readily soluble in warm ether and in hot glacial acetic acid. Sodium and boiling amyl alcohol reduce it to a tetrahydroretene, whilst if it be heated with phosphorus and hydriodic acid to 260 °C, a dodecahydride is formed. Chromic acid oxidizes it to retene quinone, phthalic acid and acetic acid. It forms a picrate which melts at 123-124 °C.

The presence of traces of retene in the air is an indicator of forest fires; it is a major product of pyrolysis of conifer trees. ^* It is also present in effluents from wood pulp and paper mills. Retene, together with cadalene and ip-iHMN, is a biomarker of higher plants, which makes it useful for paleobotanic analysis of rock sediments.

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Petroleum products | Polycyclic aromatic hydrocarbons