The simple QMOT model of a carbonyl (formaldehyde) is completely compatible with more conventional (VBT) bonding.Polarization of the HOMO towards O has implications for reactivity as well.Nucleophiles will preferentially interact with the LUMO at theĪtom/group with the larger coefficient.Ramifications for predicting and rationalizing reactivity patterns. The MO diagram for this prototype carbonyl has significant.The MO’s of O-containing molecules predict the existence of lone pairs of ē.MOT does not always lead to simple correspondence with.12 ē valence electrons between O and CH2.The lower energy π MO that is formed i s polarized towards the O, and the higher energy π* orbital is polarized towards the C.
In the case of the π and π* orbitals, the oxygen p orbital is lower in energy than the CH2 p.The thumbnail images on the left provide access to enlarged graphics as well as 3D-models (VRML) of the orbitals, respectively.įurther informations on AOs are available from the gallery of hydrogenic orbitals and hybrid orbitals. (which are potentially positively charged reagents with a low-energy unoccupied molecular orbital LUMO, which interacts with the HOMO of the substrate) always attack the formaldehyde in this case) always attack the carbon atom rather than the oxygen. Which interacts with the LUMO of the corresponding substrates, i.e. Therefore nucleophiles (potentially negatively charged reagents with a high-energy occupied molecular orbital HOMO, Has the larger AO coefficient at the oxygen atom). 9) is characterized by larger atom orbital coefficients at the carbon atom (the opposite hold for its counterpart orbital no. 9) is the anti-bonding orbital of the π-bond.įurthermore, the LUMO (orbital no. However, the lowest unoccupied molecular orbital ( LUMO, orbital no.
a free electron pair of the oxygen atom) constitutes the highest occupied molecular orbital ( HOMO, orbital no. 7 below) is not the highest occupied orbital,īut the non-bonding (i.e. Note that the bonding orbital of the π-bond of formaldehyde constructed from the 2p z AOs (orbital no. The remaining six valence MOs are constructed from the carbon and oxygen Involve the carbon and oxygen 1s-core orbitals in bonding and anti-bonding combination, respectively (total of four electrons, orbitals not shown here). With increasing energy of the orbitals (from bottom to top), the number of nodal planes (not necessarily real "planar" planes) increases and the symmetry decreases.įor formaldehyde, there are 16 electrons (CH 2O, 6 + 2×1 + 8 = 16 electrons) and eight occupied orbitals. Nodal planes (not necessarily real "planar" planes) were ψ passes through zero and changes sign are indicated in orange.Ĭlick on the small images below with blue background below to obtain an enlarged view - the images with black background provide links to the corresponding 3D-models (VRML-type models) these linksīelow on the right, the schematic drawing indicates the major contributions of atomic orbitals (AOs) to the molecular orbitals (MOs) of formaldehyde. The different colors (yellow and blue) represent regions with opposite sign of the wave function ψ they resemble the spatial volume around the nuclei of the molecule in which the electrons are found with the corresponding certainty. Surfaces of the electron density (ψ 2), i.e. All MO representations are 90% or 90-25% iso-contour probability This page gives an overview on the molecular orbitals of formaldehyde calculated by DFT methods using a B3LYP/6-311++G** basis set. Though the exact Schrödinger equation is unsolvable for many electron systems suchĪs molecules, the solution can be numerically approximated by ab initio or density functional (DFT) theory. The molecular orbitals (MOs) of molecules can be constructed by linear combination of atomic orbitals (LCAO).