Triple bond

A triple bond in chemistry is a chemical bond between two atoms involving six bonding electrons instead of the usual two in a covalent single bond. Triple bonds are stronger than the equivalent single bonds or double bonds, with a bond order of three. The most common triple bond is in a nitrogen N₂ molecule; the second most common is that between two carbon atoms, which can be found in alkynes. Other functional groups containing a triple bond are cyanides and isocyanides. Some diatomic molecules, such as diphosphorus^[1] and carbon monoxide, are also triple bonded. In skeletal formulae the triple bond is drawn as three parallel lines (≡) between the two connected atoms.^[2]^[3]^[4]

Chemical compounds with triple bond(s)

acetylene, H−C≡C−H	cyanogen, N≡C−C≡N	carbon monoxide, C≡O

Bonding

Triple bonding can be explained in terms of orbital hybridization. In the case of acetylene, each carbon atom has two sp-orbitals and two p-orbitals. The two sp-orbitals are linear, with 180° bond angles, and occupy the x-axis in the cartesian coordinate system. The p-orbitals are perpendicular 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-sp sigma bond. At the same time the p_z-orbitals approach and together they form a p_z-p_z pi-bond. Likewise, the other pair of p_y-orbitals form a p_y-p_y pi-bond. The result is formation of one sigma bond and two pi bonds.

In the bent bond model, the triple bond can also formed by the overlapping of three sp³ lobes without the need to invoke a pi-bond.^[5]

Triple bonds between elements heavier than oxygen

Structure of hexa(tert-butoxy)ditungsten(III), an example of a metal-metal triple bond.

Many elements beyond oxygen can form triple bonds. These bonds are common in some transition metals. Hexa(tert-butoxy)ditungsten(III) and Hexa(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 molecule diphosphorus, which has roughly half the bond-dissociation energy of dinitrogen.^[1]

References

^ ^a ^b Huber, K. P.; Herzberg, G. (1979). Molecular Spectra and Molecular Structure IV. Constants of Diatomic Molecules. New York: Van Nostrand. ISBN 978-0442233945.
^ March, Jerry (1985), Advanced Organic Chemistry: Reactions, Mechanisms, and Structure, 3rd edition, New York: Wiley, ISBN 9780471854722, OCLC 642506595
^ Organic Chemistry 2nd Ed. John McMurry
^ Pyykkö, Pekka; Riedel, Sebastian; Patzschke, Michael (2005). "Triple-Bond Covalent Radii". Chemistry: A European Journal. 11 (12): 3511–20. doi:10.1002/chem.200401299. PMID 15832398.
^ Advanced Organic Chemistry Carey, Francis A., Sundberg, Richard J. 5th ed. 2007
^ Chisholm, Malcolm H.; Gallucci, Judith C.; Hollandsworth, Carl B. (2006). "Crystal and molecular structure of W₂(OBut)₆ and electronic structure calculations on various conformers of W₂(OMe)₆". Polyhedron. 25 (4): 827–833. doi:10.1016/j.poly.2005.07.010.
^ .Listemann, Mark L.; Schrock, Richard R. (1985). "Multiple metal carbon Bonds. 35. A General Route to tri-tert-Butoxytungsten Alkylidyne complexes. Scission of Acetylenes by Ditungsten Hexa-tert-butoxide". Organometallics. 4: 74–83. doi:10.1021/om00120a014.

[Herzberg-1] Huber, K. P.; Herzberg, G. (1979). Molecular Spectra and Molecular Structure IV. Constants of Diatomic Molecules. New York: Van Nostrand. ISBN 978-0442233945.

[2] March, Jerry (1985), Advanced Organic Chemistry: Reactions, Mechanisms, and Structure, 3rd edition, New York: Wiley, ISBN 9780471854722, OCLC 642506595

[3] Organic Chemistry 2nd Ed. John McMurry

[4] Pyykkö, Pekka; Riedel, Sebastian; Patzschke, Michael (2005). "Triple-Bond Covalent Radii". Chemistry: A European Journal. 11 (12): 3511–20. doi:10.1002/chem.200401299. PMID 15832398.

[5] Advanced Organic Chemistry Carey, Francis A., Sundberg, Richard J. 5th ed. 2007

[6] Chisholm, Malcolm H.; Gallucci, Judith C.; Hollandsworth, Carl B. (2006). "Crystal and molecular structure of W₂(OBut)₆ and electronic structure calculations on various conformers of W₂(OMe)₆". Polyhedron. 25 (4): 827–833. doi:10.1016/j.poly.2005.07.010.

[7] .Listemann, Mark L.; Schrock, Richard R. (1985). "Multiple metal carbon Bonds. 35. A General Route to tri-tert-Butoxytungsten Alkylidyne complexes. Scission of Acetylenes by Ditungsten Hexa-tert-butoxide". Organometallics. 4: 74–83. doi:10.1021/om00120a014.

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