Chemistry:Phosphorane

The structure of a typical phosphorane group.

A phosphorane (IUPAC name: λ⁵-phosphane) is a functional group in organophosphorus chemistry with pentavalent phosphorus. It has the general formula PR₅. The parent hydride compound is the hypothetical molecule PH₅. The derivative pentaphenylphosphorane (Ph₅P) is stable.

Phosphoranes adopt a trigonal bipyramidal molecular geometry with the two apical bonds longer than the three equatorial bonds. Hypervalent bonding is described by inclusion of non-bonding MOs, as also invoked for the closely related molecule phosphorus pentafluoride.

Phosphoranes of the type R₃P=CR₂ are more common and more important. Phosphoranes are also considered to be one of the resonance structures of ylides, these compounds feature a tetrahedral phosphorus center including a phosphorus–carbon double bond. These compounds are used as reagents in the Wittig reaction, for instance methylenetriphenylphosphorane or Ph₃P=CH₂.

See also

• Organophosphorus chemistry
• Phosphane