Textbook Question
Which is a better leaving group, HO⁻ or H2O? Explain your answer.
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Ch. 12 - Substitution and Elimination: Reactions of Haloalkanes
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. 12 - Substitution and Elimination: Reactions of HaloalkanesProblem 68
Mullins 1st EditionCh. 12 - Substitution and Elimination: Reactions of HaloalkanesProblem 68Chapter 11, Problem 68
The following chlorocyclohexane undergoes neither Sₙ2 nor E2 under the conditions shown. Why?
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Analyze the structure of chlorocyclohexane: Chlorocyclohexane is a cyclohexane ring with a chlorine atom attached to one of the carbons. The chlorine atom is a good leaving group, but the reaction mechanism depends on the conditions provided.
Understand the Sₙ2 mechanism: The Sₙ2 mechanism requires a strong nucleophile and a substrate that is not sterically hindered. In the case of chlorocyclohexane, the cyclohexane ring creates steric hindrance, especially if the chlorine is in the equatorial position, making it difficult for the nucleophile to attack the carbon bearing the chlorine.
Understand the E2 mechanism: The E2 mechanism requires a strong base and an anti-periplanar arrangement of the β-hydrogen and the leaving group. In chlorocyclohexane, the anti-periplanar geometry may not be achievable due to the conformational constraints of the cyclohexane ring, especially if the chlorine is in the equatorial position.
Consider the reaction conditions: If the conditions provided do not include a strong nucleophile (for Sₙ2) or a strong base (for E2), neither mechanism will proceed. Additionally, steric hindrance and conformational constraints further inhibit these reactions.
Conclude why neither mechanism occurs: The combination of steric hindrance, conformational constraints, and potentially unsuitable reaction conditions prevents both the Sₙ2 and E2 mechanisms from occurring in this case.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Sₙ2 Mechanism
The Sₙ2 mechanism is a bimolecular nucleophilic substitution reaction where a nucleophile attacks an electrophile, leading to the simultaneous displacement of a leaving group. This reaction typically occurs in primary or secondary substrates due to steric accessibility. In the case of chlorocyclohexane, steric hindrance from the cyclohexane ring can prevent effective nucleophilic attack, making Sₙ2 unlikely.
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General Mechanism
E2 Mechanism
The E2 mechanism is a concerted elimination reaction where a base abstracts a proton while a leaving group departs, resulting in the formation of a double bond. This reaction is favored in secondary and tertiary substrates due to steric factors. In chlorocyclohexane, the ring structure may hinder the necessary anti-periplanar arrangement of the leaving group and the hydrogen, thus inhibiting E2 reactivity.
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09:36Drawing the E2 Mechanism.
Steric Hindrance
Steric hindrance refers to the prevention of chemical reactions due to the spatial arrangement of atoms within a molecule. In bulky molecules like chlorocyclohexane, the presence of large groups can obstruct the approach of nucleophiles or bases, making reactions like Sₙ2 and E2 less favorable. Understanding steric hindrance is crucial for predicting the reactivity of organic compounds.
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Related Practice
Textbook Question
When trans-4-bromocyclohexanol is treated with base, an intramolecular substitution reaction occurs to give a cyclic ether. This product does not form when cis-4-bromocyclohexanol is reacted under the same conditions. Explain these observations.
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Textbook Question
Give a mechanism for the following substitution and elimination reactions.
(b)
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Textbook Question
Give a mechanism for the following substitution and elimination reactions.
(c)
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Textbook Question
The following substitution reaction, between a strong base and a 1° haloalkane, occurs in a single step via backside displacement. Yet it is not technically an SN2 reaction. Why?
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Textbook Question
In addition to using mCPBA, epoxides can be synthesized from alkenes in the two-step process shown. Give a mechanism for each step of the process.
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