Textbook Question
The dye alizarin normally forms an orange solution when dissolved. However, if KOEt is added to the solution, it turns blue very rapidly. Rationalize this result.
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Ch. 21 - Conjugated Systems I: Stability and Addition Reactions
Mullins1st EditionOrganic Chemistry: A Learner Centered ApproachISBN: 9780137566471
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Table of contents
- Ch. 2 - General Chemistry Translated: Finding the Electrons114
- Ch. 3 - Alkanes and Cycloalkanes: Properties and Conformational Analysis109
- Ch. 4 - Acids and Bases: Electron Flow144
- Ch. 5 - Chemical Reaction Analysis: Thermodynamics and Kinetics118
- Ch. 6 - Stereoisomerism: Arrangement of Atoms in Space112
- Ch. 7 - Principles of Green (Organic) Chemistry3
- Ch. 8 - Alkenes I: Properties and Electrophilic Additions158
- Ch. 9 - Alkenes II: Oxidation and Reduction150
- Ch. 10 - Alkynes: Electrophilic Addition and Redox Reactions101
- Ch. 11 - Properties and Synthesis of Alkyl Halides: Radical Reactions108
- Ch. 12 - Substitution and Elimination: Reactions of Haloalkanes172
- Ch. 13 - Alcohols, Ethers and Related Compounds: Substitution and Elimination239
- Ch. 14 - Structural Identification I: Infrared Spectroscopy and Mass Spectrometry54
- Ch. 15 - Structural Identification II: Nuclear Magnetic Resonance Spectroscopy93
- Ch. 16 - Metals in Organic Chemistry48
- Ch. 17 - Carbonyl Addition Reactions: Aldehydes and Ketones45
- Ch. 18 - Nucleophilic Acyl Substitution I: Carboxylic Acids18
- Ch. 19 - Nucleophilic Acyl Substitution II: Carboxylic Acid Derivatives39
- Ch. 20 - Enolates: Carbonyl Addition and Substitution13
- Ch. 21 - Conjugated Systems I: Stability and Addition Reactions56
- Ch. 22 - Conjugated Systems II: Pericyclic Reactions54
- Ch. 23 - Benzene I: Aromatic Stability and Substitution Reactions64
- Ch. 24 - Benzene II: Reactions Influenced by the Aromatic Ring62
- Ch. 25 - Amines: Structure, Reactions, and Synthesis27
- Ch. 26 - Amino Acids, Proteins, and Peptide Synthesis9
- Ch. 27 - Carbohydrates, Nucleic Acids, and Lipids54
Mullins1st EditionOrganic Chemistry: A Learner Centered ApproachISBN: 9780137566471Not the one you use?Change textbook
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Mullins 1st EditionCh. 21 - Conjugated Systems I: Stability and Addition ReactionsProblem 54b
Mullins 1st EditionCh. 21 - Conjugated Systems I: Stability and Addition ReactionsProblem 54bChapter 20, Problem 54b
Which of the following reactions would you expect to be faster/more favorable in each pair? Why?
(b) 
Verified step by step guidance1
Identify the type of reaction: Both reactions involve the abstraction of a hydrogen atom by a bromine radical (Br•) from a cyclohexane derivative, leading to the formation of a cyclohexyl radical.
Analyze the stability of the radicals formed: In the first reaction, the radical is formed on a saturated cyclohexane ring, while in the second reaction, the radical is formed on a cyclohexene ring, which has an alkene group.
Consider the effect of the alkene: The presence of the alkene in the cyclohexene can stabilize the radical through hyperconjugation and resonance, making the radical more stable compared to the radical formed in the saturated cyclohexane.
Evaluate the reaction rate: Reactions that form more stable intermediates (radicals, in this case) are generally faster and more favorable. Therefore, the reaction involving the cyclohexene is expected to be faster due to the additional stabilization of the radical.
Conclude which reaction is faster: Based on the stability of the radicals, the reaction involving the cyclohexene is more favorable and faster than the reaction involving the saturated cyclohexane.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Radical Stability
Radical stability is crucial in determining the rate of radical reactions. More stable radicals form faster and are more favorable. Stability is influenced by factors like hyperconjugation and resonance. In the image, the radical formed in the second reaction is stabilized by the adjacent double bond, making it more favorable.
Recommended video:
Guided course
03:43
The radical stability trend.
Bromine Radical Reactivity
Bromine radicals are highly reactive species that can abstract hydrogen atoms from organic molecules, forming new radicals. The reactivity of bromine radicals is influenced by the stability of the resulting radical. In the image, the bromine radical reacts with cyclohexane and cyclohexene, with the latter being more favorable due to radical stabilization.
Recommended video:
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05:20Using the Hammond Postulate to describe radical bromination.
Allylic Position
The allylic position refers to the carbon atom adjacent to a double bond. Radicals formed at allylic positions are more stable due to resonance stabilization, which allows the radical to be delocalized over the π system. In the image, the second reaction involves an allylic radical, making it faster and more favorable compared to the first reaction.
Recommended video:
1:26Reactions at the Allylic Position Concept 1
Related Practice
Textbook Question
Predict the product of the following reactions.
(d)
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Textbook Question
Which of the following reactions would you expect to be faster/more favorable in each pair? Why?
(c)
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Textbook Question
Draw the molecular orbital picture of octa-1,3,5,7-tetraene, indicating which is the HOMO and which is the LUMO.
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Textbook Question
On a per alkene basis, which would have the more negative heat of hydrogenation?
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Textbook Question
How many 𝝅 electrons are involved in the conjugated system for each of the following molecules?
(a)
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