Ch.1 - Structure and Bonding

Wade9th EditionOrganic ChemistryISBN: 9780135213728Not the one you use?Change textbook

Wade 9th Edition

Ch.1 - Structure and Bonding

Problem 8e,f

Chapter 1, Problem 8e,f

For each of the following compounds, draw the important resonance forms. Indicate which structures are major and minor contributors or whether they have the same energy.
(e) [CH₃C(OH)₂]⁺
(f) [CH₂CHNH]^–

Verified step by step guidance

Identify the functional groups and charges in each compound. The first compound is a carbocation with a hydroxyl group, and the second compound is an amine anion.

For the carbocation [CH3C(OH)2]+, recognize that the positive charge is on the carbon atom. Consider resonance structures where the lone pairs on the oxygen atoms can be used to stabilize the positive charge by forming a double bond with the carbon.

Draw the resonance structures for [CH3C(OH)2]+. The major contributor will be the structure where the positive charge is delocalized onto the oxygen, as oxygen is more electronegative and can better stabilize the charge.

For the anion [CH2CHNH]-, identify the lone pair on the nitrogen atom. Consider resonance structures where the lone pair can form a double bond with the adjacent carbon, moving the negative charge to the carbon atom.

Draw the resonance structures for [CH2CHNH]-. The major contributor will be the structure where the negative charge is on the nitrogen, as nitrogen is more electronegative and can better stabilize the charge. Compare the energy levels of the resonance forms to determine major and minor contributors.

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Key Concepts

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

Resonance Structures

Resonance structures are different Lewis structures for a molecule that depict the same arrangement of atoms but differ in the placement of electrons. They help illustrate the delocalization of electrons within a molecule, which can stabilize the molecule. The true structure is a hybrid of all resonance forms, with major contributors having lower energy and more stability.

Major and Minor Contributors

In resonance theory, major contributors are resonance structures that are more stable and lower in energy, often having full octets and minimal charge separation. Minor contributors are less stable due to factors like incomplete octets or high charge separation. Identifying these contributors helps predict the molecule's behavior and properties.

Charge Distribution in Resonance

Charge distribution in resonance structures affects their stability. Structures with charges on more electronegative atoms are generally more stable. For example, in [CH3C(OH)2]+, placing positive charge on the carbon is less stable than on oxygen due to oxygen's higher electronegativity. Understanding charge distribution is crucial for determining major and minor resonance contributors.

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Related Practice

Textbook Question

For each of the following compounds, draw the important resonance forms. Indicate which structures are major and minor contributors or whether they have the same energy.

(g)

(h)

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Textbook Question

For each of the following compounds, draw the important resonance forms. Indicate which structures are major and minor contributors or whether they have the same energy.

(d) [H₂CNO₂]^–

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Textbook Question

Draw the important resonance forms for the following molecules and ions.

(d) NO₃^–

(e) NO₂^–

(f)

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Textbook Question

For each of the following compounds, draw the important resonance forms. Indicate which structures are major and minor contributors or whether they have the same energy.

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Textbook Question

Draw the important resonance forms of the following cations and anions:

(c)

(d)

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Textbook Question

Use resonance structures to identify the areas of high and low electron density in the following compounds:

(c)

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