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The Dewar–Chatt–Duncanson model is a model in PtCl3(C2H4).html" ;"title="platinum.html" ;"title="/nowiki>platinum">PtCl3(C2H4)">platinum.html" ;"title="/nowiki>platinum">PtCl3(C2H4)sup>.H2O the C−C bond length has increased to 134 picometres from 133 pm for ethylene. In the nickel compound Ni(C2H4)(PPh3)2 the value is 143 pm.
The interaction also causes carbon atoms to "rehybridise" from sp2 towards sp3, which is indicated by the bending of the hydrogen atoms on the ethylene back away from the metal.
The Dewar–Chatt–Duncanson model is a model in organometallic chemistry
Organometallic chemistry is the study of organometallic compounds, chemical compounds containing at least one chemical bond between a carbon atom of an organic molecule and a metal, including alkali, alkaline earth, and transition metals, and so ...
that explains the chemical bond
A chemical bond is a lasting attraction between atoms or ions that enables the formation of molecules and crystals. The bond may result from the electrostatic force between oppositely charged ions as in ionic bonds, or through the sharing of ...
ing in transition metal alkene complex
In organometallic chemistry, a transition metal alkene complex is a coordination compound containing one or more alkene ligands. Such compounds are intermediates in many catalytic reactions that convert alkenes to other organic products.Elschenbro ...
es. The model is named after Michael J. S. Dewar
Michael James Steuart Dewar (24 September 1918 – 10 October 1997) was an American theoretical chemist.
Education and early life
Dewar was the son of Scottish parents, Annie Balfour (Keith) and Francis Dewar. He received the degrees of Bache ...
, Joseph Chatt
Joseph Chatt (6 November 1914 – 19 May 1994) was a renowned British researcher in the area of inorganic and organometallic chemistry. His name is associated with the description of the pi-bond between transition metals and alkenes, the Dewar– ...
and L. A. Duncanson.
The alkene
In organic chemistry, an alkene is a hydrocarbon containing a carbon–carbon double bond.
Alkene is often used as synonym of olefin, that is, any hydrocarbon containing one or more double bonds.H. Stephen Stoker (2015): General, Organic, an ...
donates electron density
In quantum chemistry, electron density or electronic density is the measure of the probability of an electron being present at an infinitesimal element of space surrounding any given point. It is a scalar quantity depending upon three spatial va ...
into a π-acid metal d-orbital
In atomic theory and quantum mechanics, an atomic orbital is a Function (mathematics), function describing the location and wave-like behavior of an electron in an atom. This function can be used to calculate the probability of finding any electr ...
from a π-symmetry bonding orbital
In theoretical chemistry, the bonding orbital is used in molecular orbital (MO) theory to describe the attractive interactions between the atomic orbitals of two or more atoms in a molecule. In MO theory, electrons are portrayed to move in waves. ...
between the carbon atoms. The metal donates electrons back from a (different) filled d-orbital into the empty π* antibonding orbital
In chemical bonding theory, an antibonding orbital is a type of molecular orbital that weakens the chemical bond between two atoms and helps to raise the energy of the molecule relative to the separated atoms. Such an orbital has one or more no ...
. Both of these effects tend to reduce the carbon-carbon bond order, leading to an elongated C−C distance and a lowering of its vibrational frequency.
In Zeise's salt
Zeise's salt, potassium trichloro(ethylene)platinate(II), is the chemical compound with the formula K platinum">PtCl3(C2H4).html" ;"title="platinum.html" ;"title="/nowiki>PtCl3(C2H4)">platinum.html"_;"title="/nowiki>platinum">PtCl3(C2H4)·H2O.__Th ...
KIn silico
In biology and other experimental sciences, an ''in silico'' experiment is one performed on computer or via computer simulation. The phrase is pseudo-Latin for 'in silicon' (correct la, in silicio), referring to silicon in computer chips. It ...
calculations show that 75% of the binding energy is derived from the forward donation and 25% from backdonation.Herrmann/Brauer: ''Synthetic Methods of Organometallic and Inorganic Chemistry'' Georg Thieme, Stuttgart, 1996 This model is a specific manifestation of the more general π backbonding
In chemistry, π backbonding, also called π backdonation, is when electrons move from an atomic orbital on one atom to an appropriate symmetry antibonding orbital on a ''π-acceptor ligand''. It is especially common in the organometallic che ...
model.
References
{{DEFAULTSORT:Dewar-Chatt-Duncanson Model Organometallic chemistry Chemical bonding