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Ch. 8 - Delocalized Electrons: Their Effect on Stability, pKa, and the Products of a Reaction • Aromaticity and Electronic Effects: An Introduction to the Reactions of Benzene
Bruice - Organic Chemistry 8th Edition
Bruice8th EditionOrganic ChemistryISBN: 9780135213711Not the one you use?Change textbook
All textbooksBruice 8th EditionCh. 8 - Delocalized Electrons: Their Effect on Stability, pKa, and the Products of a Reaction • Aromaticity and Electronic Effects: An Introduction to the Reactions of BenzeneProblem 4b
Chapter 9, Problem 4b

Which species in each pair is more stable?
b. Comparison of two chemical structures to determine which conjugated intermediate is more stable.

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1
Identify the structural features of each species in the pair. Look for elements such as the presence of resonance structures, inductive effects, and hyperconjugation, which can influence stability.
Examine the resonance structures: Determine if either species can delocalize charge through resonance. More resonance structures generally increase stability.
Consider the inductive effect: Analyze if there are electronegative atoms or groups that can withdraw electron density through sigma bonds, stabilizing the species.
Evaluate hyperconjugation: Check if there are alkyl groups adjacent to a positively charged center that can donate electron density through hyperconjugation, enhancing stability.
Compare the overall stability: After analyzing resonance, inductive effects, and hyperconjugation, determine which species has more stabilizing factors and is therefore more stable.

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Key Concepts

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

Stability of Chemical Species

The stability of chemical species refers to their tendency to maintain their structure and resist change. Factors influencing stability include the energy of the species, resonance structures, and steric hindrance. More stable species typically have lower energy and are less reactive, making them less likely to undergo chemical transformations.
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Resonance Structures

Resonance structures are different ways of drawing the same molecule that illustrate the delocalization of electrons. A molecule with multiple resonance forms can distribute its electron density more evenly, leading to increased stability. The actual structure of the molecule is a hybrid of these forms, and the more resonance forms a species has, the more stable it generally is.
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Steric Hindrance

Steric hindrance refers to the repulsion between bulky groups within a molecule that can affect its stability and reactivity. When atoms or groups are too close together, they can create strain, making the molecule less stable. Understanding steric effects is crucial for predicting the stability of different species, especially in organic compounds where spatial arrangement plays a significant role.
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Related Practice
Textbook Question

Between 1865 and 1890, other possible structures were proposed for benzene, such as those shown here. Considering what nineteenth-century chemists knew about benzene, which is a better proposal for benzene’s structure: Dewar benzene or Ladenburg benzene? Why?

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Textbook Question

Which species in each pair is more stable?

a.

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Textbook Question

Draw resonance contributors for each of the following species and rank them in order of decreasing contribution to the resonance hybrid. Then draw the resonance hybrid.

b.

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Textbook Question

Which species in each pair is more stable?

c.

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Textbook Question

How many dibrominated products could each of the compounds form if stereoisomers are included?

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Textbook Question

Which species in each pair is more stable?

d.

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