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|Section2= |Section3= }} 4-Nitrophenol (also called ''p''-nitrophenol or 4-hydroxynitrobenzene) is a phenolic compound that has a nitro group at the opposite position of hydroxyl group on the benzene ring. ==Properties== 4-Nitrophenol shows two polymorphs in the crystalline state. The alpha-form is colorless pillars, unstable at room temperature, and stable toward sunlight. The beta-form is yellow pillars, stable at room temperature, and gradually turns red upon irradiation of sunlight. Usually 4-nitrophenol exists as a mixture of these two forms. In solution, 4-nitrophenol has a dissociation constant (p''K''a) of 7.16 at 22 °C. Solution of 4-nitrophenol alone appears colorless or pale yellow, whereas its phenolic salts tend to develop a bright yellow color. This color-changing property makes this compound useful as a pH indicator. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「4-Nitrophenol」の詳細全文を読む スポンサード リンク
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