<unk>  has a wide range of functions across all disciplines of chemistry. The four premier categories of reactivity involve metal-carbonyl catalysis, radical chemistry, cation and anion chemistries.<unk> ordination chemistry Energy level scheme of the σ and π orbitals of<unk>  HOMO of<unk>  is a σ MO. LUMO of<unk>  is a π* antibonding MO. Most metals form<unk> ordination<unk> mplexes<unk> ntaining<unk> valently attached<unk> . Only metals in lower oxidation states will<unk> mplex with<unk>  ligands. This is because there must be sufficient electron density to facilitate back-donation from the metal dxz-orbital, to the π* molecular orbital from<unk> . The lone pair on the<unk>  atom in<unk>  also donates electron density to the dx²−y² on the metal to form a sigma bond. This electron donation is also exhibited with the cis effect, or the labilization of<unk>  ligands in the cis position. Nickel<unk> yl, for example, forms by the direct<unk> mbination of<unk>  and nickel metal: : Ni + 4<unk>  → Ni<unk> 4 (1 bar, 55 °C) For this reason, nickel in any tubing or part must not<unk> me into prolonged<unk> ntact with<unk> . Nickel<unk> yl decomposes readily back to Ni and<unk>  upon<unk> ntact with hot surfaces, and this method is used for the industrial purification of nickel in the Mond process. In nickel<unk> yl and other<unk> yls, the electron pair on the<unk>  interacts with the metal; the<unk>  donates the electron pair to the metal. In these situations,<unk>  is called the<unk> yl ligand. One of the most important metal<unk> yls is iron pentacarbonyl, Fe<unk> 5: Structure of iron pentacarbonyl. Iron pentacarbonyl. Many metal–CO<unk> mplexes are prepared by decarbonylation of organic solvents, not from<unk> . For instance, iridium trichloride and triphenylphosphine react in boiling 2-methoxyethanol or DMF to afford IrCl<unk> (PPh3)2. Metal<unk> yls in<unk> ordination chemistry are usually studied using infrared spectroscopy. Organic and main group chemistry In the presence of strong acids and water,<unk>  reacts with alkenes to form<unk> ylic acids in a process known as the Koch–Haaf reaction. In the Gattermann–Koch reaction, arenes are<unk> nverted to benzaldehyde derivatives in the presence of AlCl3 and HCl. Organolithium<unk> mpounds (e.g. butyl lithium) react with<unk> , but these reactions have little scientific use. Although<unk>  reacts with<unk> ations and<unk> ions, it is relatively nonreactive toward organic<unk> mpounds without the intervention of metal catalysts. With main group reagents,<unk>  undergoes several noteworthy reactions. Chlorination of<unk>  is the industrial route to the important<unk> mpound phosgene. With borane<unk>  forms the adduct H3BCO, which is isoelectronic with the acetylium cation H3CCO+.<unk>  reacts with sodium to give products resulting from C−C<unk> upling such as sodium acetylenediolate 2·. It reacts with molten potassium to give a mixture of an organometallic<unk> mpound, potassium acetylenediolate 2·, potassium benzenehexolate 6, and potassium rhodizonate 2·. The<unk> mpounds cyclohexanehexone or triquinoyl (C6O6) and cyclopentanepentone or leuconic acid (C5O5), which so far have been obtained only in trace amounts, can be regarded as polymers of<unk> . At pressures exceeding 5 GPa,<unk> <unk> nverts to polycarbonyl, an solid polymer that is metastable at atmospheric pressure but is explosive. Laboratory preparation<unk>  is<unk> nveniently produced in the laboratory by the dehydration of formic acid or oxalic acid, for example with<unk> ncentrated sulfuric acid. Another method is heating an intimate mixture of powdered zinc metal and calcium<unk> ate, which releases<unk>  and leaves behind zinc oxide and calcium oxide: :Zn + CaCO3 → ZnO + CaO +<unk>  Silver nitrate and iodoform also afford<unk> : :CHI3 + 3AgNO3 + H2O → 3HNO3 +<unk>  + 3AgI Finally, metal oxalate salts release<unk>  upon heating, leaving a<unk> ate as byproduct: : → +
Carbon monoxide
Nitrosamine
Mustard gas
Nicosan
Metaldehyde
Lewisite
Nitrous oxide 
Asbestos