Osmium tetroxide

Osmium tetroxide (OsO₄) is a volatile, highly toxic osmium compound that oxidizes organic molecules and stains biological specimens for electron microscopy.

Alkene dihydroxylation: The conversion of an alkene into a vicinal diol by adding hydroxyl groups across its carbon–carbon double bond. Osmium tetroxide adds across alkene double bonds, forming intermediates that yield neighboring hydroxyl groups.
Transmission electron microscopy: A microscopy technique that forms images by transmitting electrons through a thin specimen. Osmium-treated biological samples gain electron contrast for transmission imaging.
Osmium: A dense, hard, bluish-white transition metal with atomic number 76. Osmium tetroxide is the volatile oxide of this element.
Sharpless asymmetric dihydroxylation: A catalytic alkene dihydroxylation that uses chiral ligands to favor one enantiomer of a vicinal diol. It harnesses osmium tetroxide chemistry to make chiral diols selectively.
Osmate ester: A compound containing an osmium–oxygen–carbon framework, often formed during oxidation of an alkene by osmium tetroxide. This intermediate links alkene addition to formation of the diol.
Scanning electron microscopy: A microscopy technique that scans a specimen with an electron beam to image its surface. Osmium coating can make poorly conducting specimens more suitable for high-resolution surface imaging.
Osmium oxidation states: The formal charge states that osmium adopts in compounds, including the +8 state in osmium tetroxide. Osmium’s +8 oxidation state accounts for the compound’s strong oxidizing character.
Potassium permanganate: A purple manganese compound widely used as a strong oxidizing agent. It can oxidize alkenes too, but often causes less selective or more extensive oxidation.
Syn addition: A reaction in which two groups add to the same face of a multiple bond. Osmium-mediated alkene oxidation typically places both new oxygen groups on the same face.
Lipid staining: The selective coloring or labeling of lipids to make them visible in microscopy or analysis. Osmium tetroxide reacts with unsaturated lipids, making membranes and lipid-rich structures conspicuous.

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