phosphorus exists in a formal oxidation state of less than III are uncommon, but examples are known for each class. Organophosphorus(0) species are debatably illustrated by the carbene adducts, [P(NHC)]2, where NHC is an N-heterocyclic carbene. With the formulae (RP)n and (R2P)2, respectively, compounds of phosphorus(I) and (II) are generated by reduction of the related organophosphorus(III) chlorides: 5 PhPCl2 + 5 Mg → (PhP)5 + 5 MgCl2 2 Ph2PCl + Mg → Ph2P-PPh2 + MgCl2 Diphosphenes, with the formula R2P2, formally contain phosphorus-phosphorus double bonds. These phosphorus(I) species are rare but are stable provided that the organic substituents are large enough to prevent catenation. Many mixed-valence compounds are known, e.g. the cage P7(CH3)3. See also Organophosphates Organophosphites Organothiophosphates Activity-based proteomics a branch of biochemistry that often relies on organophosphorus probes to interrogate enzyme activities Bihar school meal poisoning incident References External links organophosphorus chemistry @ users.ox.ac.uk; @ www.chem.wisc.edu NMR predictor for organophosphorus compound chemical shifts from Alan Brisdon's Research Group Link Functional groups