Ch.8 - Covalent Compounds: Bonding Theories and Molecular Structure

McMurry8th EditionChemistryISBN: 9781292336145Not the one you use?Change textbook

McMurry 8th Edition

Ch.8 - Covalent Compounds: Bonding Theories and Molecular Structure

Problem 115c

Chapter 8, Problem 115c

Cyclooctatetraene dianion, C₈H₈^2-, is an organic ion with the structure shown. Considering only the p bonds and not the s bonds, cyclooctatetraene dianion can be described by the following energy diagrams of its p molecular orbitals:
(c) Complete the MO energy diagram by assigning the appropriate numbers of p electrons to the various molecular orbitals, indicating the electrons using up/down arrows 1c T2.

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Identify the total number of π electrons in the cyclooctatetraene dianion. Since each carbon contributes one electron and there are two extra electrons due to the dianion charge, calculate the total π electrons.

Understand the molecular orbital (MO) theory for cyclic compounds, which states that π electrons will fill the available molecular orbitals starting from the lowest energy level.

Draw the molecular orbital diagram with the appropriate number of energy levels for cyclooctatetraene. Typically, for an eight-membered ring, there will be four bonding and four antibonding π orbitals.

Fill the molecular orbitals with the calculated number of π electrons, starting from the lowest energy orbital. Use up and down arrows to represent the electrons, keeping in mind the Pauli Exclusion Principle and Hund's Rule.

Ensure that the total number of arrows (each representing an electron) matches the total number of π electrons calculated in step 1. Check that lower energy orbitals are fully filled before electrons are placed in higher energy orbitals.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Molecular Orbital Theory

Molecular Orbital (MO) Theory describes how atomic orbitals combine to form molecular orbitals that can be occupied by electrons. In this theory, electrons are delocalized over the entire molecule rather than being associated with individual atoms. The energy levels of these MOs are determined by the energies of the atomic orbitals involved in their formation, and they can be filled according to the Aufbau principle, Hund's rule, and the Pauli exclusion principle.

Electron Configuration in MOs

The electron configuration in molecular orbitals involves assigning electrons to the available MOs based on their energy levels. Electrons fill the lowest energy orbitals first, and each orbital can hold a maximum of two electrons with opposite spins. For cyclooctatetraene dianion, the total number of p electrons must be determined and distributed among the MOs, which include bonding, non-bonding, and antibonding orbitals.

Cyclooctatetraene Structure and Stability

Cyclooctatetraene is a cyclic compound that can exist in a non-planar conformation, which affects its stability and reactivity. The dianion form, C8H8^2-, has additional electrons that influence its molecular orbital configuration. Understanding the structure and stability of cyclooctatetraene is crucial for predicting its behavior in reactions and its electronic properties, particularly in relation to its p orbital interactions.

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Textbook Question

The water molecule has similar bond vibrations to carbon dioxide. Decide whether the symmetric, asymmetric, and bending vibrations in water will result in the absorption of IR radiation.

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Textbook Question

Cyclooctatetraene dianion, C₈H₈^2-, is an organic ion with the structure shown. Considering only the p bonds and not the s bonds, cyclooctatetraene dianion can be described by the following energy diagrams of its p molecular orbitals:

(a) What is the hybridization of the 8 carbon atoms?

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Textbook Question

The dichromate ion, Cr2O72-, has neither Cr¬Cr nor O¬O bonds. (b) How many outer-shell electrons does each Cr atom have in your electron-dot structure? What is the likely geometry around the Cr atoms?

Values of Ea = 6.3 kJ>mol and A = 6.0 * 108>1M # s2 have been measured for the bimolecular reaction: NO1g2 + F21g2S NOF1g2 + F1g2 (b) The product of the reaction is nitrosyl fluoride. Its formula is usually written as NOF, but its structure is actually ONF. Is the ONF molecule linear or bent?

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Textbook Question

Bond vibrations for the symmetric and asymmetric stretch in methane are illustrated below. Decide whether each vibration will result in the absorption of IR radiation. Arrows indicate the movement of atoms during the vibration.

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Textbook Question

(b) Three of the p molecular orbitals are bonding, three are antibonding, and two are nonbonding, meaning that they have the same energy level as isolated p orbitals. Which is which?

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