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Isolobal principle
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<p>In <a href="/facts/Organometallic_chemistry/bhqFz2P0">organometallic chemistry</a>, the isolobal principle (more formally known as the isolobal analogy) is a strategy used to relate the structure of <a href="/facts/Organic_compound/gqCNaN45">organic</a> and <a href="/facts/Inorganic_compound/TfFfzxSz">inorganic</a> molecular fragments in order to predict <a href="/facts/Chemical_bond/ArNUMnIB">bonding</a> properties of organometallic compounds. <a href="/facts/Roald_Hoffmann/DHMcXIff">Roald Hoffmann</a> described molecular fragments as isolobal "if the number, <a href="/facts/Molecular_symmetry/BrDxAkTK">symmetry</a> properties, approximate energy and shape of the <a href="/facts/Frontier_orbital/XyofpH0p">frontier orbitals</a> and the number of <a href="/facts/Electron/L0KBo5cW">electrons</a> in them are similar – not identical, but similar." One can predict the bonding and <a href="/facts/Reactivity_(chemistry)/PuJ2pmRT">reactivity</a> of a lesser-known species from that of a better-known species if the two molecular fragments have similar frontier orbitals, the <a href="/facts/Highest_occupied_molecular_orbital/XyofpH0p">highest occupied molecular orbital</a> (HOMO) and the <a href="/facts/Lowest_unoccupied_molecular_orbital/XyofpH0p">lowest unoccupied molecular orbital</a> (LUMO). Isolobal compounds are analogues to <a href="/facts/Isoelectronic/SbzuaI05">isoelectronic</a> compounds that share the same number of <a href="/facts/Valence_electron/mXPA15VP">valence electrons</a> and structure. A graphic representation of isolobal structures, with the isolobal pairs connected through a double-headed arrow with half an orbital below, is found in Figure 1. </p> <p>For his work on the isolobal analogy, Hoffmann was awarded the <a href="/facts/Nobel_Prize_in_Chemistry/8Nb8Ajjy">Nobel Prize in Chemistry</a> in 1981, which he shared with <a href="/facts/Kenichi_Fukui/3Pj2XcXw">Kenichi Fukui</a>. In his Nobel Prize lecture, Hoffmann stressed that the isolobal analogy is a useful, yet simple, model and thus is bound to fail in certain instances. </p>