A phosphorane (

IUPAC The International Union of Pure and Applied Chemistry (IUPAC ) is an international federation of National Adhering Organizations working for the advancement of the chemical sciences, especially by developing nomenclature and terminology. It is ...

name: λ⁵-phosphane) is a

functional group In organic chemistry, a functional group is a substituent or moiety in a molecule that causes the molecule's characteristic chemical reactions. The same functional group will undergo the same or similar chemical reactions regardless of the res ...

organophosphorus chemistry Organophosphorus compounds are organic compounds containing phosphorus. They are used primarily in pest control as an alternative to chlorinated hydrocarbons that persist in the environment. Some organophosphorus compounds are highly effective ins ...

with

pentavalent In chemistry, the valence (US spelling) or valency (British spelling) of an element is the measure of its combining capacity with other atoms when it forms chemical compounds or molecules. Description The combining capacity, or affinity of a ...

phosphorus Phosphorus is a chemical element with the symbol P and atomic number 15. Elemental phosphorus exists in two major forms, white phosphorus and red phosphorus, but because it is highly reactive, phosphorus is never found as a free element on Ea ...

. It has the general formula PR₅. The parent

hydride In chemistry, a hydride is formally the anion of hydrogen( H−). The term is applied loosely. At one extreme, all compounds containing covalently bound H atoms are called hydrides: water (H2O) is a hydride of oxygen, ammonia is a hydride of ...

compound is the hypothetical molecule PH₅. The derivative

pentaphenylphosphorane Pentaphenylphosphorus is an organic phosphorane containing five phenyl groups connected to a central phosphorus atom. The phosphorus atom is considered to be in the +5 oxidation state. The chemical formula could be written as P(C6H5)5 or Ph5P, whe ...

(Ph₅P) is stable. Phosphoranes adopt a

trigonal bipyramidal molecular geometry In chemistry, a trigonal bipyramid formation is a molecular geometry with one atom at the center and 5 more atoms at the corners of a triangular bipyramid. This is one geometry for which the bond angles surrounding the central atom are not ident ...

with the two

apical Apical means "pertaining to an apex". It may refer to: * Apical ancestor, refers to the last common ancestor of an entire group, such as a species (biology) or a clan (anthropology) *Apical (anatomy), an anatomical term of location for features l ...

bonds longer than the three equatorial bonds.

Hypervalent bonding In chemistry, a hypervalent molecule (the phenomenon is sometimes colloquially known as expanded octet) is a molecule that contains one or more main group elements apparently bearing more than eight electrons in their valence shells. Phosphorus p ...

is described by inclusion of non-bonding MOs, as also invoked for the closely related molecule

phosphorus pentafluoride Phosphorus pentafluoride, P F5, is a phosphorus halide. It is a colourless, toxic gas that fumes in air. Preparation Phosphorus pentafluoride was first prepared in 1876 by the fluorination of phosphorus pentachloride using arsenic trifluoride, ...

.G. L. Miessler and D. A. Tarr “Inorganic Chemistry” 3rd Ed, Pearson/Prentice Hall publisher, . Phosphoranes of the type R₃P=CR₂ are more common and more important. Phosphoranes are also considered to be one of the resonance structures of

ylide An ylide or ylid () is a neutral dipolar molecule containing a formally negatively charged atom (usually a carbanion) directly attached to a heteroatom with a formal positive charge (usually nitrogen, phosphorus or sulfur), and in which both ato ...

s, these compounds feature a tetrahedral phosphorus center including a phosphorus–carbon double bond. These compounds are used as reagents in the

Wittig reaction The Wittig reaction or Wittig olefination is a chemical reaction of an aldehyde or ketone with a triphenyl phosphonium ylide called a Wittig reagent. Wittig reactions are most commonly used to convert aldehydes and ketones to alkenes. Most ...

, for instance

methylenetriphenylphosphorane Methylenetriphenylphosphorane is an organophosphorus compound with the formula Ph3PCH2. It is the parent member of the phosphorus ylides, popularly known as Wittig reagents. It is a highly polar, highly basic species. Preparation and use Methylen ...

or Ph₃P=CH₂.

References

{{Reflist Organophosphanes Functional groups

See also

References