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Ch.9 - Molecular Geometry and Bonding Theories
All textbooksBrown 14th EditionCh.9 - Molecular Geometry and Bonding TheoriesProblem 121
Chapter 9, Problem 121

Antibonding molecular orbitals can be used to make bonds to other atoms in a molecule. For example, metal atoms can use appropriate d orbitals to overlap with the π*2p orbitals of the carbon monoxide molecule. This is called d-π backbonding. (a) Draw a coordinate axis system in which the y-axis is vertical in the plane of the paper and the x-axis horizontal. Write 'M' at the origin to denote a metal atom. (b) Now, on the x-axis to the right of M, draw the Lewis structure of a CO molecule, with the carbon nearest the M. The CO bond axis should be on the x-axis. (c) Draw the CO π*2p orbital, with phases (see the 'Closer Look' box on phases) in the plane of the paper. Two lobes should be pointing toward M. (d) Now draw the dxy orbital of M, with phases. Can you see how they will overlap with the π*2p orbital of CO? (e) What kind of bond is being made with the orbitals between M and C, σ or π? (f) Predict what will happen to the strength of the CO bond in a metal–CO complex compared to CO alone.

Verified step by step guidance
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Step 1: Begin by drawing a coordinate axis system on your paper. Place the y-axis vertically and the x-axis horizontally. At the origin, where the axes intersect, write 'M' to represent the metal atom.
Step 2: On the x-axis, to the right of 'M', draw the Lewis structure of a carbon monoxide (CO) molecule. Ensure that the carbon atom is closest to the metal atom 'M', and the CO bond axis is aligned with the x-axis.
Step 3: Next, illustrate the π*2p antibonding orbital of the CO molecule. This orbital will have two lobes, with opposite phases, pointing towards the metal atom 'M'. The phases can be represented by shading or using '+' and '-' signs.
Step 4: Now, draw the dxy orbital of the metal atom 'M'. This orbital should also have lobes with phases, and it lies in the plane of the paper. The orientation of the dxy orbital should allow for overlap with the π*2p orbital of CO.
Step 5: Consider the type of bond formed between the metal and carbon. Since the overlap involves the π*2p orbital of CO and the dxy orbital of the metal, this interaction is a π bond. Predict that the CO bond strength in the metal–CO complex will decrease compared to CO alone due to the backbonding interaction.
Related Practice
Textbook Question
Many compounds of the transition-metal elements contain direct bonds between metal atoms. We will assume that the z-axis is defined as the metal–metal bond axis. (d) Sketch the energylevel diagram for the Sc2 molecule, assuming that only the 3d orbital from part (a) is important.
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Textbook Question
The organic molecules shown here are derivatives of benzene in which six-membered rings are 'fused' at the edges of the hexagons.

(e) Benzene, naphthalene, and anthracene are colorless, but tetracene is orange. What does this imply about the relative HOMO–LUMO energy gaps in these molecules? See the 'Chemistry Put to Work' box on orbitals and energy.
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Textbook Question

The organic molecules shown here are derivatives of benzene in which six-membered rings are 'fused' at the edges of the hexagons.

(b) Suppose you are given a sample of one of the compounds. Could combustion analysis be used to determine unambiguously which of the three it is?

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Textbook Question

Methyl isocyanate, CH3NCO, was made infamous in 1984 when an accidental leakage of this compound from a storage tank in Bhopal, India, resulted in the deaths of about 3800 people and severe and lasting injury to many thousands more. (a) Draw a Lewis structure for methyl isocyanate.

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