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Ch. 2 - Acids and Bases; Functional Groups
Wade - Organic Chemistry 9th Edition
Wade9th EditionOrganic ChemistryISBN: 9780135213728Not the one you use?Change textbook
All textbooksWade 9th EditionCh. 2 - Acids and Bases; Functional GroupsProblem 1b
Chapter 2, Problem 1b

The C=O double bond has a dipole moment of about 2.4 D and a bond length of about 1.23 Å.
b. Use this information to evaluate the relative importance of the following two resonance contributors:

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1
Identify the two resonance structures for the given molecule. The first structure has a double bond between the carbon and oxygen, while the second structure has a single bond with a negative charge on oxygen and a positive charge on carbon.
Understand that resonance structures are a way to represent the delocalization of electrons in a molecule. The actual structure is a hybrid of these resonance forms.
Evaluate the dipole moment and bond length information provided. A dipole moment of 2.4 D and a bond length of 1.23 Å suggest a significant contribution from the polar resonance structure.
Consider the stability of each resonance structure. The structure with the double bond (C=O) is generally more stable due to the full octet on both atoms and no formal charges.
Conclude that while both resonance structures contribute to the overall hybrid, the structure with the double bond is likely more important due to its stability and the given dipole moment and bond length, which align more closely with this structure.

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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 ways of drawing the same molecule that illustrate the delocalization of electrons. They help in understanding the actual electronic structure of a molecule, which is a hybrid of all possible resonance forms. In the context of the question, the two resonance contributors depict how the C=O bond can be represented with different charges and electron distributions, affecting the molecule's stability and reactivity.
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Dipole Moment

The dipole moment is a measure of the separation of positive and negative charges in a molecule, indicating its polarity. A higher dipole moment suggests a stronger polar character, which can influence the molecule's interactions and stability. In this case, the C=O bond's dipole moment of 2.4 D indicates significant polarity, which is essential for evaluating the resonance contributors' relative importance.
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How dipole-dipole forces work.

Bond Length

Bond length is the distance between the nuclei of two bonded atoms, which can provide insights into bond strength and stability. A bond length of 1.23 Å for the C=O double bond suggests a strong interaction due to the overlap of atomic orbitals. Understanding bond length is crucial when evaluating resonance structures, as it can indicate how electron delocalization affects the overall stability of the molecule.
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Related Practice
Textbook Question

1. Draw the Lewis structure.

2. Show how the bond dipole moments (and those of any nonbonding pairs of electrons) contribute to the molecular dipole moment.

3. Estimate whether the compound will have a large, small, or zero dipole moment.

g. HCN

h. CH3CHO

i. H2C=NH

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Textbook Question

The C=O double bond has a dipole moment of about 2.4 D and a bond length of about 1.23 Å.

a. Calculate the amount of charge separation in this bond.

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Textbook Question

The N—F bond is more polar than the N—H bond, but NF3 has a smaller dipole moment than NH3. Explain this curious result.

NF3

μ= 0.2 D

NH3

μ = 1.5 D

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Textbook Question

1. Draw the Lewis structure.

2. Show how the bond dipole moments (and those of any nonbonding pairs of electrons) contribute to the molecular dipole moment.

3. Estimate whether the compound will have a large, small, or zero dipole moment.

d. CH3F

e. CF4

f. CH3OH

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