The Carbon Monoxide Molecule

The carbon monoxide molecule can be described in conventional valence bond terms as having two canonical forms one having the carbene-like structure in which divalent carbon is linked to oxygen by a double bond and the other a dinitrogen-like form, in which both atoms carry a lone pair and are linked by a triple bond [Eq (2.1)]. 

carbon monoxide is a metastable molecule that is almost inert under mild conditions, but becomes very reactive when subjected to high pressure or elevated temperature and can be easily activated by catalysts. 

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In SCF problems, there are some cases where the wave function must have a lower symmetry than the molecule. This is due to the way that the wave function is constructed from orbitals and basis functions. For example, the carbon monoxide molecule might be computed with a wave function of 41 symmetry even though the molecule has a C-xt symmetry. This is because the orbitals obey C41 constraints. 

Fig. 1.15. Energy levels in the carbon monoxide molecule. (Adapted from H. B. Gray and G. P. Haight, Basic Principles of Chemistry, W.

Even if it is assumed that the reaction is ionic, Occam s Razor would lead to the conclusion that the system is too complex and that the effort to keep it ionic is too great. It is difficult to undersand why step 8c is slow and why a simple uncharged complex would not be equally reasonable. We prefer a mechanism in which the carbon monoxide molecule is adsorbed parallel to the surface and in which the oxygen orbitals as well as the carbon orbitals of C=0 bond electrons interact with the metal. It seems reasonable that hydrogenolysis occurs exclusively only because the oxygen is held in some way while the two bonds are broken and it finally desorbs as water. The most attractive picture would be (a) adsorption of CO and H2 with both atoms on the surface... 

Write the configuration of the ground state of the carbon monoxide molecule. 

In the following discussion use is made of an equation that has been formulated by the method given earlier in a discussion of the equation for resonance between a single bond and a double bond11 and of the interatomic distances in the carbon monoxide molecule and carbon dioxide molecule.13 The potential function for the bond is assumed to have the form... 

The discussion of electronic energy curves also throws light on such questions as the structure of the carbon monoxide molecule. The empirical study of potential curves obtained from band spectral data has shown18 that for atoms in the first row of the periodic system a double bond leads 18 An account of this work will be published at some future time. 

Detailed investigation of the hydrogenation of the carbon monoxide molecule, as homogeneously catalyzed by the HCo O) /... 

The parameter n in Equation (9.20) is called the reduced mass. For the carbon monoxide molecule CO, /i is defined by... 

If we consider the surface of quartz to be divisible into two areas on which the lengths of life of the carbon monoxide molecule are 1 and the amount of gas adsorbed on the total area at a pressure p will evidently be... 

Problem 7-2. What type of bond is found in the carbon monoxide molecule, CO This molecule is very slightly polar but, surprisingly, the negative end of the molecule is the carbon atom. (Why is this surprising ) Compare the force constant of CO with that of a molecule with a typical double bond, O2, and with that of a molecule with a typical triple bond, N2. Suggest a reasonable qualitative description of the electronic structure of CO that explains these observations. 

As a second illustration let us consider the carbon monoxide molecule. For years there was discussion as to which of the structures... 

Fia. VII-4.—Some observed energy levels for the carbon monoxide molecule, as determined by the analysis of spectra. The first thirteen vibrational levels are shown for the normal electronic state of the molecule, and the rotational levels are Bhown for the lowest vibrational state. 

Fig. 5.18 (a) Total electron density contours for the carbon monoxide molecule. The carbon atom is on the left (b) Total electron density contours for the dinitrogen molecule. [From Bader, R. F. W. Bandrauk, A. D. J. Chem. Phys. 1968,49, 1653. Reproduced with permission.]... 

Considering the molecular orbital diagram of carbon monoxide (Fig. 5.201 and the discussion concerning hybridization and energy (pages 225-227). predict which end of the carbon monoxide molecule will be the more basic (i.e., will donate electrons more readily and form the stronger, direct covalent bond)... 

A simple view of the mode of bonding of the carbon monoxide molecule to the surfaces of the transition metals and in their carbonyl complexes is well known and is thoroughly described in the literature.4 These metals have unfilled d-orbitals (or holes in their d-band), and the molecule in the linear form is held by a push-pull bond in which charge is transferred from the 5a orbital of the molecule into the metal s d-band, while there is back-donation of charge from the top of the d-band into the molecule s vacant... 

It may seem perfectly reasonable that the carbon monoxide molecule could crash into the nitrogen dioxide molecule in just the right way and steal the oxygen atom for itself. Analysis of the reaction, however, has detected the presence of the substance NOa, which is neither a reactant nor a product of the reaction. One explanation for this finding is that the reaction proceeds in two steps ... 

The general conclusion was that rather weak bonding was established between the cation and the carbon monoxide molecule. The scheme of the bonding was depicted as essentially a transfer of-the carbon lone pair to the cation empty orbitals with a variable extent back-donation from the cation filled orbitals to the antibonding II orbitals of the CO molecule. This bonding scheme generally resulted in an electron deficient carbonyl carbon especially in view of the weak back-donation to the II molecular orbitals of CO. This makes the carbon particularly suitable for nucleophilic attacks by electrophiles. 

From what has been said so far, we would expect any diatomic molecule with a polar bond (between atoms with different electronegativities) to exhibit a dipole moment. Although this is generally true, the observed dipole moments of diatomic molecules are sometimes smaller than expected. For example, the carbon monoxide molecule CO has a dipole moment of only 0.11 D, much smaller than expected from the polarity of the CO bond. This discrepancy is most likely caused by the lone pairs of electrons on the atoms, which make large contributions to the dipole moment in opposition to that from the bond polarity. We will not explore the details of this situation here. The dipole moments of some representative diatomic molecules are listed in Table 13.3. 

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