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When fumarate reacts with D2O in the presence of the enzyme fumarase, only one isomer of the product is formed, as shown here. Is the enzyme catalyzing a syn or an anti addition of D2O?
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Ch. 6 - The Reactions of Alkenes • The Stereochemistry of Addition Reactions
Bruice8th EditionOrganic ChemistryISBN: 9780135213711
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TOC.tableOfContents
- Ch. 1 - Remembering General Chemistry: Electronic Structure and Bonding31
- Ch. 2 - Acids and Bases: Central to Understanding Organic Chemistry84
- Ch. 3 - An Introduction to Organic Compounds: Nomenclature, Physical Properties, and Structure183
- Ch. 4 - Isomers: The Arrangement of Atoms in Space121
- Ch. 5 - Alkenes: Structure, Nomenclature, and an Introduction to Reactivity • Thermodynamics and Kinetics83
- Ch. 6 - The Reactions of Alkenes • The Stereochemistry of Addition Reactions175
- Ch. 7 - The Reactions of Alkynes • An Introduction to Multistep Synthesis119
- Ch. 8 - Delocalized Electrons: Their Effect on Stability, pKa, and the Products of a Reaction • Aromaticity and Electronic Effects: An Introduction to the Reactions of Benzene148
- Ch. 9 - Substitution and Elimination Reactions of Alkyl Halides212
- Ch. 10 - Reactions of Alcohols, Ethers, Epoxides, Amines, and Sulfur-Containing Compounds131
- Ch. 11 - Organometallic Compounds60
- Ch. 12 - Radicals90
- Ch. 13 - Mass Spectrometry; Infrared Spectroscopy; UV/Vis Spectroscopy62
- Ch. 14 - NMR Spectroscopy95
- Ch. 15 - Reactions of Carboxylic Acids and Carboxylic Acid Derivatives123
- Ch. 16 - Reactions of Aldehydes and Ketones • More Reactions of Carboxylic Acid Derivatives141
- Ch. 17 - Reactions at the Alpha-Carbon101
- Ch. 18 - Reactions of Benzene and Substituted Benzenes144
- Ch. 19 - More About Amines • Reactions of Heterocyclic Compounds49
- Ch. 20 - The Organic Chemistry of Carbohydrates80
- Ch. 21 - Amino Acids, Peptides, and Proteins57
- Ch. 22 - Catalysis in Organic Reactions and in Enzymatic Reactions35
- Ch. 23 - The Organic Chemistry of the Coenzymes—Compounds Derived from Vitamins1
- Ch. 28 - Pericyclic Reactions58
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Bruice 8th EditionCh. 6 - The Reactions of Alkenes • The Stereochemistry of Addition ReactionsProblema 96
Bruice 8th EditionCh. 6 - The Reactions of Alkenes • The Stereochemistry of Addition ReactionsProblema 96Capitolo 6, Problema 96
a. Propose a mechanism for the following reaction:
b. Is the initially formed carbocation primary, secondary, or tertiary?
c. Is the rearranged carbocation primary, secondary, or tertiary?
d. Why does the rearrangement occur?
Guida verificata passo dopo passo1
Step 1: Analyze the reaction. The starting material is an alkene, and the reagent is HBr. This indicates that the reaction is an electrophilic addition of HBr to the alkene. The alkene will act as a nucleophile, attacking the proton (H⁺) from HBr, leading to the formation of a carbocation intermediate.
Step 2: Determine the initially formed carbocation. When the alkene attacks H⁺, the double bond breaks, and the positive charge is placed on the carbon that can best stabilize the carbocation. In this case, the initially formed carbocation is secondary because the positive charge is on a carbon attached to two other carbons.
Step 3: Consider carbocation rearrangement. Carbocations can undergo rearrangement to form a more stable carbocation. In this case, a hydride shift occurs, moving a hydrogen atom (along with its bonding electrons) from a neighboring carbon to the carbocation center. This results in the formation of a tertiary carbocation, which is more stable due to increased hyperconjugation and inductive effects.
Step 4: Explain why the rearrangement occurs. The rearrangement occurs because tertiary carbocations are more stable than secondary carbocations. Stability increases due to the greater number of alkyl groups donating electron density through hyperconjugation and inductive effects, stabilizing the positive charge.
Step 5: Complete the reaction mechanism. After the rearrangement, the bromide ion (Br⁻) attacks the tertiary carbocation, forming the final product. The major product is the one where Br⁻ adds to the more stable tertiary carbocation, while the minor product results from Br⁻ adding to the secondary carbocation before rearrangement.
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Hydrohalogenation
Hydrohalogenation is an electrophilic addition reaction where a hydrogen halide (like HBr) adds across a double bond in an alkene. The reaction typically involves the formation of a carbocation intermediate, where the more stable carbocation is favored. This process is crucial for understanding how the halogen and hydrogen are added to the alkene, influencing the final product's structure.
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04:07
General properties of hydrohalogenation.
Carbocation Stability
Carbocation stability is determined by the degree of alkyl substitution around the positively charged carbon atom. Tertiary carbocations are the most stable due to hyperconjugation and inductive effects from surrounding alkyl groups, followed by secondary and primary carbocations. Recognizing the stability of the initially formed and rearranged carbocations is essential for predicting the major product of the reaction.
Video consigliato:
05:58Determining Carbocation Stability
Carbocation Rearrangement
Carbocation rearrangement occurs when a less stable carbocation transforms into a more stable one, often through hydride or alkyl shifts. This process is driven by the stability of the resulting carbocation, which can lead to different products. Understanding why and how rearrangements happen is key to predicting the outcome of reactions involving carbocations, such as in hydrohalogenation.
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00:47Understanding why carbocations shift.
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