Textbook Question
Rationalize the ranking of increasing reaction rate of the benzylic halides shown.
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Ch. 24 - Benzene II: Reactions Influenced by the Aromatic Ring
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. 24 - Benzene II: Reactions Influenced by the Aromatic RingProblem 56
Mullins 1st EditionCh. 24 - Benzene II: Reactions Influenced by the Aromatic RingProblem 56Chapter 23, Problem 56
In light of your answers to Assessments 24.54 and 24.55, rank the following based on the rate of protonation of the alkene (1 = most basic, 6 = least basic). [Ignore the fact that the alkene may not be the most basic site in the molecule.]
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Analyze the substituents attached to the benzene ring in each molecule. Substituents can influence the electron density of the alkene through inductive effects or resonance effects, which affect the basicity of the alkene.
Consider the electron-donating or electron-withdrawing nature of each substituent. Electron-donating groups (e.g., alkyl groups) increase electron density on the alkene, making it more basic, while electron-withdrawing groups (e.g., nitro groups) decrease electron density, making the alkene less basic.
Rank the molecules based on the substituents: (1) The molecule with the strongest electron-donating group will have the most basic alkene. (2) The molecule with the strongest electron-withdrawing group will have the least basic alkene.
Evaluate the substituents: -CH3 (electron-donating), -Cl (weak electron-withdrawing), -H (neutral), -N(CH3) (electron-donating due to lone pair resonance), -C=O (strong electron-withdrawing), -NO2 (very strong electron-withdrawing).
Assign ranks based on the above analysis: (1 = most basic, 6 = least basic). Molecules with electron-donating groups will rank higher, while those with electron-withdrawing groups will rank lower.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Protonation of Alkenes
Protonation of alkenes involves the addition of a proton (H+) to the double bond, forming a carbocation. The stability of the resulting carbocation significantly influences the rate of protonation. More stable carbocations, such as tertiary ones, are formed more readily, making the corresponding alkene more basic. Understanding the factors that stabilize carbocations is crucial for predicting protonation rates.
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Electronic Effects of Substituents
The presence of different substituents on an alkene can greatly affect its basicity and the rate of protonation. Electron-donating groups (EDGs) enhance basicity by stabilizing the positive charge of the carbocation, while electron-withdrawing groups (EWGs) decrease basicity by destabilizing it. Recognizing how these groups influence electron density is essential for ranking the alkenes based on their protonation rates.
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Resonance Stabilization
Resonance stabilization occurs when a molecule can be represented by multiple valid Lewis structures, distributing electron density over several atoms. In the context of alkenes, substituents that can participate in resonance can stabilize the carbocation formed during protonation. This stabilization can significantly enhance the basicity of the alkene, making it more favorable for protonation compared to alkenes without such resonance effects.
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03:43The radical stability trend.
Related Practice
Textbook Question
A chemist attempted to oxidize a primary alcohol to a carboxylic acid using chromic acid. The product shown was obtained as a major component in the mixture. Suggest an arrow-pushing mechanism that accounts for its formation. [Think about what chromic acid would normally do to a phenol and make a list of bonds formed and bonds broken.]
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Phenol oxidation can be coupled with other reactions to form new C―C bonds using reactions studied previously. Predict the product of the following series of reactions.
(a)
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Textbook Question
Phenol oxidation can be coupled with other reactions to form new C―C bonds using reactions studied previously. Predict the product of the following series of reactions.
(b)
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