A phosphorane (IUPAC name: û<sup>5</sup>-phosphane) is a functional group in organophosphorus chemistry with pentavalent phosphorus. Phosphoranes have the general formula PR<sub>5</sub>.
Phosphoranes of the type PX<sub>5</sub> 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.
The parent hydride compound is the hypothetical molecule PH<sub>5</sub>.
Pentaphenylphosphorane (Ph<sub>5</sub>P) is stable.
Pentaalkoxyphosphoranes are more common with electronegative substituents. Examples of P(OR)<sub>5</sub> (R = alkyl), have however been prepared by reaction of phosphites with benzene alkyl sulfenates:
Phosphoranes of the type R<sub>3</sub>P=CR<sub>2</sub> 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 phosphorusâÂÂcarbon double bond. These compounds are used as reagents in the Wittig reaction, for instance methylenetriphenylphosphorane or Ph<sub>3</sub>P=CH<sub>2</sub>.