Atriple bond inchemistry is achemical bond between twoatoms involving sixbonding electrons instead of the usual two in acovalent single bond. Triple bonds are stronger than the equivalentsingle bonds ordouble bonds, with abond order of three. The most common triple bond is in anitrogen N2 molecule; the second most common is that between twocarbon atoms, which can be found inalkynes. Otherfunctional groups containing a triple bond arecyanides andisocyanides. Some diatomic molecules, such asdiphosphorus[1] andcarbon monoxide, are also triple bonded. Inskeletal formulae the triple bond is drawn as three parallel lines (≡) between the two connected atoms.[2][3][4]
 |  |  |
| acetylene, H−C≡C−H | cyanogen, N≡C−C≡N | carbon monoxide, C≡O |
Triple bonding can be explained in terms oforbital hybridization. In the case of acetylene, each carbon atom has twosp-orbitals and twop-orbitals. The two sp-orbitals are linear, with 180°bond angles, and occupy the x-axis in thecartesian coordinate system. The p-orbitals areperpendicular to the sp-orbitals on the y-axis and the z-axis. When the atoms approach each other, the sp orbitals overlap to form an sp-spsigma bond. At the same time the pz-orbitals approach and together they form a pz-pzpi-bond. Likewise, the other pair of py-orbitals form a py-py pi-bond. The result is formation of one sigma bond and two pi bonds.
In thebent bond model, the triple bond can also formed by the overlapping of three sp3 lobes without the need to invoke a pi-bond.[5]
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Many elements beyond oxygen can form triple bonds. These bonds are common in some transition metals.Hexa(tert-butoxy)ditungsten(III) andHexa(tert-butoxy)dimolybdenum(III) are well known examples, in which the metal-metal bond distance is about 233 pm.[6]Hexa(tert-butoxy)ditungsten(III) has attracted particular attention for its reactions with alkynes, leading to metal-carbon triple bonded compounds of the formula RC≡W(OBut)3[7]
Additionally,phosphorus can exist as the highly reactive diatomic moleculediphosphorus, which has roughly half thebond-dissociation energy of dinitrogen.[1]
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