Limonene, also known as Limonene; Lemon olein is a cyclic monoterpene that is widely present in various essential oils, especially lemon oil, citragon oil, orange oil, bergamot oil, and dill oil. Limonene contains a chiral center, including L-limonene, d-limonene optical isomers and a racemic body. At room temperature, both isomers are colorless flammable liquids with a strong and pleasant aroma; L-limonene smells of lemon/turpentine, while d-limonene smells of lemon/orange.