Domanda del libro di testo
Which of the following substitution reactions would you expect to occur more quickly? 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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TOC.tableOfContents
- 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 1: Properties and Electrophilic Additions158
- Ch. 9 - Alkenes 2: 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 1: Infrared Spectroscopy and Mass Spectrometry54
- Ch. 15 - Structural Identification 2: Nuclear Magnetic Resonance Spectroscopy93
- Ch. 16 - Metals in Organic Chemistry48
- Ch. 17 - Carbonyl Addition Reactions: Aldehydes and Ketones45
- Ch. 18 - Nucleophilic Acyl Substitution 1: Carboxylic Acids18
- Ch. 19 - Nucleophilic Acyl Substitution 2: Carboxylic Acid Derivatives39
- Ch. 20 - Enolates: Carbonyl Addition and Substitution13
- Ch. 21 - Conjugated Systems 1: Stability and Addition Reactions56
- Ch. 22 - Conjugated Systems 2: Pericyclic Reactions54
- Ch. 23 - Benzene 1: Aromatic Stability and Substitution Reactions64
- Ch. 24 - Benzene 2: 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: 9780137566471Non è quello che usi tu?Cambia libro di testo
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Mullins 1st EditionCh. 12 - Substitution and Elimination: Reactions of HaloalkanesProblema 63
Mullins 1st EditionCh. 12 - Substitution and Elimination: Reactions of HaloalkanesProblema 63Capitolo 11, Problema 63
The introduction of elimination reactions provides a second way to synthesize alkynes in a two-step process starting with an alkene. Suggest a mechanism for both steps of this process.
Guida verificata passo dopo passo1
Step 1: Analyze the starting material, which is an alkene. The first step involves the addition of bromine (Br₂) to the alkene. This reaction proceeds via an electrophilic addition mechanism, where the π-electrons of the alkene attack the bromine molecule, forming a bromonium ion intermediate.
Step 2: The bromonium ion is then attacked by a bromide ion (Br⁻), leading to the formation of a vicinal dibromide (a molecule with two bromine atoms attached to adjacent carbons). This completes the first step of the process.
Step 3: In the second step, the vicinal dibromide undergoes two consecutive elimination reactions in the presence of a strong base, sodium amide (NaNH₂). The base abstracts a proton from one of the carbons adjacent to a bromine atom, leading to the formation of a double bond and the elimination of a bromide ion.
Step 4: The second equivalent of NaNH₂ then abstracts another proton from the carbon adjacent to the remaining bromine atom, resulting in the formation of a triple bond (alkyne) and the elimination of the second bromide ion.
Step 5: The final product is an alkyne, specifically a terminal alkyne in this case, as the elimination reactions lead to the formation of a triple bond at the end of the carbon chain.
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Elimination Reactions
Elimination reactions involve the removal of atoms or groups from a molecule, resulting in the formation of a double or triple bond. In the context of synthesizing alkynes, elimination typically occurs in two steps: first, a halogen is added to an alkene, followed by a dehydrohalogenation step where a base removes a hydrogen halide, leading to the formation of an alkyne.
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00:40
Recognizing Elimination Reactions.
Mechanism of Bromination
The bromination of alkenes involves the addition of bromine (Br2) across the double bond, resulting in a vicinal dibromide. This reaction proceeds through a cyclic bromonium ion intermediate, which is then attacked by a bromide ion, leading to the formation of the dibrominated product. Understanding this mechanism is crucial for predicting the subsequent elimination step.
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00:54Mechanism of Allylic Bromination.
Base-Induced Dehydrohalogenation
In the second step of the synthesis, sodium amide (NaNH2) acts as a strong base to remove a hydrogen atom and a bromine atom from the vicinal dibromide, resulting in the formation of a triple bond. This process, known as dehydrohalogenation, is essential for converting the dibromide intermediate into the desired alkyne product, showcasing the importance of strong bases in elimination reactions.
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03:02The dehydrohalogenation mechanism.
Pratica correlata
Domanda del libro di testo
In Chapter 10, you learned how to make an alkyne by acetylide alkylation with a 1° haloalkane. Suggest a mechanism by which this reaction occurs.
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Domanda del libro di testo
When the reaction scheme in Assessment 12.63 is done on a monosubstituted alkene, at least three equivalents of base are needed. Reacting the product of step 2 with D–Cl (D is an isotope of H) incorporates deuterium at the terminal carbon. Explain these two observations.
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Domanda del libro di testo
Acetylide alkylation, from Assessment 12.61, fails to give the desired product with 2° haloalkanes. Why? What is the actual product of this reaction?
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Domanda del libro di testo
Give a mechanism for the following substitution and elimination reactions.
(a)
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Domanda del libro di testo
Suggest a bromoalkane and the conditions necessary to produce the alkenes shown.
(b)
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