Editing Carbon monoxide (section)

===Bonding and dipole moment===
The strength of the {{chem2|C\tO}} bond in carbon monoxide is indicated by the high frequency of its vibration, 2143&nbsp;cm<sup>−1</sup>.<ref name=nuCO>{{cite journal |doi=10.1139/v62-306 |title=Infrared Spectra of Carbon Monoxide and Carbon Dioxide Adsorbed on Chromia–Alumina and on Alumina |date=1962 |last1=Little |first1=L. H. |last2=Amberg |first2=C. H. |journal=Canadian Journal of Chemistry |volume=40 |issue=10 |pages=1997–2006 }}</ref> For comparison, organic carbonyls such as ketones and esters absorb at around 1700&nbsp;cm<sup>−1</sup>.

Carbon and oxygen together have a total of 10 [[electrons]] in the [[valence shell]]. Following the [[octet rule]] for both carbon and oxygen, the two atoms form a [[triple bond]], with six shared electrons in three bonding molecular orbitals, rather than the usual double bond found in organic carbonyl compounds. Since four of the shared electrons come from the oxygen atom and only two from carbon, one bonding orbital is occupied by two electrons from oxygen, forming a dative or [[dipolar bond]]. This causes a C←O [[Chemical polarity|polarization]] of the molecule, with a small negative charge on carbon and a small positive charge on oxygen. The other two bonding orbitals are each occupied by one electron from carbon and one from oxygen, forming (polar) covalent bonds with a reverse C→O polarization since oxygen is more [[electronegativity|electronegative]] than carbon. In the free carbon monoxide molecule, a net negative charge δ<sup>−</sup> remains at the carbon end and the molecule has a small [[bond dipole moment|dipole moment]] of 0.122&nbsp;[[Debye|D]].<ref>{{cite journal | last1=Scuseria | first1=Gustavo E. | last2=Miller | first2=Michael D. | last3=Jensen | first3=Frank | last4=Geertsen | first4=Jan |title=The dipole moment of carbon monoxide|journal=J. Chem. Phys. |volume=94 |issue= 10 | pages=6660 |year=1991 |doi=10.1063/1.460293|bibcode = 1991JChPh..94.6660S }}</ref>

The molecule is therefore asymmetric: oxygen is more electron dense than carbon and is also slightly positively charged compared to carbon being negative. 
[[File:Carbon-monoxide-resonance-2D.png|thumb|The most important resonance form of carbon monoxide is {{chem2|-C\tO+}}. An important minor resonance contributor is the non-octet carbenic structure :C=O.]]
Carbon monoxide has a computed fractional bond order of 2.6, indicating that the "third" bond is important but constitutes somewhat less than a full bond.<ref>{{Cite journal|last1=Martinie|first1=Ryan J.|last2=Bultema|first2=Jarred J.|last3=Vander Wal|first3=Mark N.|last4=Burkhart|first4=Brandon J.|last5=Vander Griend|first5=Douglas A.|last6=DeKock|first6=Roger L.|s2cid=11905354|date=2011-08-01|title=Bond Order and Chemical Properties of BF, CO, and N2|journal=Journal of Chemical Education|volume=88|issue=8|pages=1094–1097|doi=10.1021/ed100758t|issn=0021-9584|bibcode=2011JChEd..88.1094M}}</ref>  Thus, in valence bond terms, {{chem2|-C\tO+}} is the most important structure, while :C=O is non-octet, but has a neutral formal charge on each atom and represents the second most important resonance contributor.  Because of the lone pair and divalence of carbon in this resonance structure, carbon monoxide is often considered to be an extraordinarily stabilized [[carbene]].<ref>{{Cite book|title=Cumulenes in click reactions|last=Ulrich|first=Henri|date=2009|publisher=Wiley|others=Wiley InterScience (Online service)|isbn=9780470747957|location=Chichester, U.K.|pages=45|oclc=476311784}}</ref>  [[Isocyanide]]s are compounds in which the O is replaced by an NR (R = alkyl or aryl) group and have a similar bonding scheme.

If carbon monoxide acts as a [[Metal carbonyl|ligand]], the polarity of the dipole may reverse with a net negative charge on the oxygen end, depending on the structure of the [[coordination complex]].<ref>{{cite journal | last1 = Lupinetti | first1 = Anthony J. | last2 = Fau | first2 = Stefan | last3 = Frenking | first3 = Gernot | last4 = Strauss | first4 = Steven H. | title = Theoretical Analysis of the Bonding between CO and Positively Charged Atoms| journal = J. Phys. Chem. A | year= 1997 |volume= 101 |issue=49 |pages= 9551–9559 |doi=10.1021/jp972657l|bibcode= 1997JPCA..101.9551L }}</ref>
See also the section ''[[#Coordination_chemistry|"Coordination chemistry"]]'' below.