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Ch. 15 - Conjugated Systems, Orbital Symmetry, and Ultraviolet Spectroscopy
Wade - Organic Chemistry 9th Edition
Wade9th EditionOrganic ChemistryISBN: 9780135213728Not the one you use?Change textbook
All textbooksWade 9th EditionCh. 15 - Conjugated Systems, Orbital Symmetry, and Ultraviolet SpectroscopyProblem 27d
Chapter 15, Problem 27d

Draw the important resonance contributors for the following cations, anions, and radicals.
(d)

Verified step by step guidance
1
Identify the structure of the given species (cation, anion, or radical) and locate any atoms with lone pairs, π-bonds, or unfilled octets. These features are key to determining resonance contributors.
Determine the movement of electrons. For resonance structures, electrons can move in the form of lone pairs or π-bonds. Use curved arrows to show the electron flow. For example, a lone pair can form a π-bond, or a π-bond can shift to form a lone pair or move to an adjacent atom.
Draw the new resonance structure after the electron movement. Ensure that all atoms obey the octet rule (if applicable) and that the overall charge of the molecule remains the same.
Repeat the process to identify all possible resonance contributors. Each contributor should differ only in the placement of electrons, not the arrangement of atoms.
Evaluate the stability of each resonance structure. More stable contributors (e.g., those with full octets, minimal formal charges, or charges on more electronegative atoms) will contribute more to the resonance hybrid.

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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 the same molecule that depict the delocalization of electrons. They help illustrate how the actual structure is a hybrid of these forms, providing insight into the molecule's stability and reactivity. Understanding resonance is crucial for predicting the behavior of cations, anions, and radicals.
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Drawing Resonance Structures

Cation, Anion, and Radical Stability

The stability of cations, anions, and radicals is influenced by their electronic structure and the presence of resonance. Cations are stabilized by electron-donating groups, while anions benefit from electron-withdrawing groups. Radicals, having an unpaired electron, are stabilized by resonance as well, which can distribute the unpaired electron over multiple atoms.
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The radical stability trend.

Electrophiles and Nucleophiles

Electrophiles are species that seek electrons and are typically positively charged or electron-deficient, while nucleophiles are electron-rich species that donate electrons. Understanding the roles of these species is essential when analyzing resonance contributors, as they can influence the stability and reactivity of cations, anions, and radicals in organic reactions.
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Related Practice
Textbook Question

A solution was prepared using 0.0010 g of an unknown steroid (of molecular weight around 255) in 100 mL of ethanol. Some of this solution was placed in a 1-cm cell, and the UV spectrum was measured. This solution was found to have λmax = 235 nm, with A = 0.74.

(a) Compute the value of the molar absorptivity at 235 nm.

(b) Which of the following compounds might give this spectrum?

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Textbook Question

Draw the important resonance contributors for the following cations, anions, and radicals.

(b)

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Textbook Question

Draw the important resonance contributors for the following cations, anions, and radicals.

(c)

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Textbook Question

Draw the important resonance contributors for the following cations, anions, and radicals.

(a)

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Textbook Question

The diene lactone shown in part (a) has one electron-donating group (-OR) and one electron-withdrawing group (C=O). This diene lactone is sufficiently electron-rich to serve as the diene in a Diels–Alder reaction.


b. The Diels–Alder product A is not very stable. Upon mild heating, it reacts to produce CO2 gas and methyl benzoate (PhCOOCH3), a very stable product. Explain how this strongly exothermic decarboxylation takes place. (Hint: Under the right conditions, the Diels–Alder reaction can be reversible.)

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Textbook Question

Draw the important resonance contributors for the following cations, anions, and radicals.

(e)

(f)

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