氢键Hydrogen bond

X–H 键高度极化，氢原子几乎裸露成带部分正电荷的质子，与 Y 的孤对电子产生静电吸引，同时含有少量电荷转移（共价）成分。X–H···Y 接近直线时最强。氢键可在分子间形成，也可在分子内形成（如邻硝基苯酚），分子内氢键会降低沸点和水溶性。

The X–H bond is strongly polarised, leaving the hydrogen as a nearly bare, partially positive proton that attracts the lone pair on Y electrostatically, with a small charge-transfer (covalent) contribution. The bond is strongest when X–H···Y is close to linear. It can form between molecules or within one (as in o-nitrophenol); intramolecular hydrogen bonds lower boiling points and water solubility.

1912 年摩尔与温米尔在研究胺的碱性时提出类似观点。1920 年拉蒂默与罗德布什在路易斯的实验室明确用“氢核被两个原子共享”解释水和 HF 的缔合。1939 年鲍林在《化学键的本质》中系统讨论并推广了 hydrogen bond 一词。2011 年 IUPAC 发布了新的氢键定义。

In 1912 Moore and Winmill suggested a similar idea to explain the basicity of amines. In 1920 Latimer and Rodebush, in Lewis's laboratory, explicitly explained the association of water and HF by a hydrogen nucleus shared between two atoms. In 1939 Pauling treated the topic systematically in The Nature of the Chemical Bond and popularised the term. IUPAC issued a new definition in 2011.

氢键使 H₂O、HF、NH₃ 的沸点反常偏高，使冰的密度小于水，使乙醇与水互溶。在生物体内，DNA 双螺旋的碱基配对（A–T 两个、G–C 三个氢键）以及蛋白质的 α 螺旋和 β 折叠都靠氢键维持。1953 年沃森和克里克的 DNA 模型正是基于碱基间的氢键。

Hydrogen bonds give H₂O, HF and NH₃ abnormally high boiling points, make ice less dense than water and make ethanol miscible with water. In living systems they hold the base pairs of DNA together (two for A–T, three for G–C) and stabilise protein α-helices and β-sheets; Watson and Crick's 1953 DNA model was built on them.