Unsaturated compound

This refers to organic compounds that have a double bond (C=C) or triple bond (C≡C) between carbon atoms. Compounds with these multiple bonds in a ring structure are also considered unsaturated compounds, but aromatic rings such as benzene are excluded. Generally, unsaturated bonds easily undergo addition reactions, but aromatic rings are distinguished by the substitution reactions they undergo. Compounds that contain multiple bonds between carbon and heteroatoms (atoms other than carbon) are generally not considered unsaturated. That is, acetone CH ₃ COCH ₃ is a saturated ketone, and palmitic acid CH ₃ (CH ₂ ) ₁₄ COOH is also a saturated fatty acid. In contrast, oleic acid CH ₃ (CH ₂ ) ₇ CH=CH(CH ₂ ) ₇ COOH, which has a C=C double bond in addition to the carboxyl group -COOH, is an unsaturated fatty acid.

[Takeo Sato and Masaru Hirota, July 21, 2015]

Source: Shogakukan Encyclopedia Nipponica About Encyclopedia Nipponica Information | Legend

有機化合物のなかで炭素‐炭素原子間に二重結合（C=C）や三重結合（C≡C）をもつ化合物をいう。環状構造にこれらの多重結合をもつものも不飽和化合物に含まれるが、ベンゼンなどの芳香環は除く。一般に不飽和結合は容易に付加反応をおこすが、芳香環は置換反応を行うことで区別される。炭素とヘテロ原子（炭素以外の原子）間の多重結合を含む場合、一般には不飽和化合物とはいわない。すなわちアセトンCH₃COCH₃は飽和ケトンであり、パルミチン酸CH₃(CH₂)₁₄COOHも飽和脂肪酸である。これに対してカルボキシ基-COOHのほかにC=C二重結合をもつオレイン酸CH₃(CH₂)₇CH=CH(CH₂)₇COOHは不飽和脂肪酸である。

［佐藤武雄・廣田　穰　2015年7月21日］

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