一氧化碳Carbon monoxide

CO 与 N₂ 是等电子体，分子中有一个 σ 键和两个 π 键，键长 112.8 pm，键能约 1072 kJ mol⁻¹，是已知最强的化学键之一。虽然氧的电负性更大，但由于配位键的贡献，分子偶极矩很小（0.11 D），且负端在碳原子一侧。CO 通过碳原子上的孤对电子与过渡金属配位，形成 Ni(CO)₄ 等金属羰基化合物。

CO is isoelectronic with N₂, with one σ and two π bonds; the bond length is 112.8 pm and the bond energy about 1072 kJ mol⁻¹, one of the strongest known chemical bonds. Although oxygen is more electronegative, the dative contribution leaves only a small dipole moment (0.11 D), with the negative end on carbon. CO binds to transition metals through the lone pair on carbon, forming metal carbonyls such as Ni(CO)₄.

CO 与血红蛋白中 Fe²⁺ 的结合能力约为 O₂ 的 200 多倍，生成碳氧血红蛋白，使血液失去运氧能力，引起组织缺氧。由于无色无味，煤气、炭火或燃气热水器在通风不良处使用时容易造成中毒。轻度中毒者应迅速移到空气新鲜处，严重者需吸氧或高压氧治疗。

CO binds to the Fe²⁺ in haemoglobin more than 200 times more strongly than O₂, forming carboxyhaemoglobin and stopping the blood from carrying oxygen, so tissues are starved of oxygen. Because it has no colour or smell, poisoning easily occurs when gas, charcoal or gas water heaters are used without ventilation. Victims should be moved to fresh air at once; severe cases need oxygen or hyperbaric oxygen treatment.

工业上由焦炭与水蒸气反应制得水煤气（CO 与 H₂ 的混合物），或由天然气重整得到合成气。在高炉炼铁中，CO 把铁矿石还原为铁：Fe₂O₃ + 3CO → 2Fe + 3CO₂。合成气可在催化剂作用下制甲醇：CO + 2H₂ → CH₃OH。汽车尾气中的 CO 由催化转化器氧化为 CO₂。

Industrially, coke and steam give water gas (CO and H₂), and steam reforming of natural gas gives synthesis gas. In the blast furnace CO reduces iron ore: Fe₂O₃ + 3CO → 2Fe + 3CO₂. Synthesis gas is converted catalytically to methanol: CO + 2H₂ → CH₃OH. CO in car exhaust is oxidised to CO₂ in the catalytic converter.