Dimer (chemistry) dimerise to give the dimer "A-A". An example is a diaminocarbene, which dimerise to give a tetraaminoethylene: Carbenes are highly reactive and readily form bonds. Dicyclopentadiene is an asymmetrical dimer of two cyclopentadiene molecules that have reacted in a Diels-Alder reaction to give the product. Upon heating, it "cracks" (undergoes a retro-Diels-Alder reaction) to give identical monomers: Many nonmetallic elements occur as dimers: hydrogen, nitrogen, oxygen, the halogens, i.e. fluorine, chlorine, bromine and iodine. Noble gases can form dimers linked by van der Waals bonds, for example dihelium or diargon. Mercury occurs as a mercury(I) cation (Hg), formally a dimeric
Bromine pentafluoride an excess of fluorine: For the preparation of smaller amounts, potassium bromide is used: This route yields bromine pentafluoride almost completely free of trifluorides and other impurities. Bromine pentafluoride reacts violently with water, but when moderated by dilution with acetonitrile, it will form bromic acid and hydrofluoric acid, simple hydrolysis products: It is an extremely effective fluorinating agent, converting most uranium compounds to the hexafluoride at room temperature. Bromine pentafluoride is severely corrosive to the skin, and its vapors are irritating to the eyes, skin, and mucous membranes. Exposure to 100 ppm for a few minutes is lethal to most