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 54c
Mullins 1st EditionCh. 21 - Conjugated Systems I: Stability and Addition ReactionsProblem 54cChapter 20, Problem 54c
Which of the following reactions would you expect to be faster/more favorable in each pair? Why?
(c) 
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Identify the functional groups in each reaction. The first reaction involves a ketone, while the second involves an aldehyde.
Recall that aldehydes are generally more reactive than ketones due to less steric hindrance and the electron-withdrawing effect of the carbonyl group being more pronounced.
Consider the role of the base in the reaction. The base will likely deprotonate the alpha hydrogen, leading to the formation of an enolate ion.
Compare the acidity of the alpha hydrogens in both compounds. The alpha hydrogen in the aldehyde is more acidic than in the ketone, making it easier to deprotonate.
Conclude that the reaction involving the aldehyde is expected to be faster/more favorable due to the higher reactivity and acidity of the alpha hydrogen compared to the ketone.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Aldol Condensation
Aldol condensation is a reaction where enolates, formed from aldehydes or ketones, react with carbonyl compounds to form β-hydroxy ketones or aldehydes. This reaction is base-catalyzed and involves the formation of a new carbon-carbon bond. Understanding the stability of the enolate ion and the electrophilicity of the carbonyl carbon is crucial for predicting the reaction's favorability.
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Crossed Aldol
Enolate Ion Formation
Enolate ions are formed when a base abstracts an alpha hydrogen from a carbonyl compound, resulting in a resonance-stabilized anion. The acidity of the alpha hydrogen and the strength of the base influence the formation of enolates. In the given reactions, the presence of a carbonyl group increases the acidity of the alpha hydrogen, making enolate formation more favorable in the top reaction.
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Carbonyl Reactivity
Carbonyl compounds are highly reactive due to the polarization of the carbon-oxygen double bond, making the carbon electrophilic. This reactivity is crucial in reactions like aldol condensation, where the carbonyl carbon acts as an electrophile. The presence of the carbonyl group in the top reaction increases the electrophilicity, making the reaction more favorable compared to the bottom reaction, which lacks this group.
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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?
(b)
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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
How many 𝝅 electrons are involved in the conjugated system for each of the following molecules?
(a)
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Textbook Question
Predict the product of the following reactions.
(i)
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