Domanda del libro di testo
Rank the following species in each set from best nucleophile to poorest nucleophile.
c. H2O and NH3 in methanol
d. Br−, Cl−, I− in methanol
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Ch. 9 - Substitution and Elimination Reactions of Alkyl Halides
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. 9 - Substitution and Elimination Reactions of Alkyl HalidesProblema 76
Bruice 8th EditionCh. 9 - Substitution and Elimination Reactions of Alkyl HalidesProblema 76Capitolo 9, Problema 76
a. Identify the substitution products that form when 2-bromo-2-methylpropane is dissolved in a mixture of 80% ethanol and 20% water.
b. Explain why the same products are obtained when 2-chloro-2-methylpropane is dissolved in a mixture of 80% ethanol and 20% water.
Guida verificata passo dopo passo1
Step 1: Recognize that 2-bromo-2-methylpropane is a tertiary alkyl halide. Tertiary alkyl halides typically undergo substitution reactions via the SN1 mechanism in polar protic solvents like ethanol and water.
Step 2: In the SN1 mechanism, the reaction begins with the ionization of the alkyl halide. The C-Br bond breaks heterolytically, forming a carbocation (2-methyl-2-propyl carbocation) and a bromide ion (Br⁻). Write the ionization step as: \( \text{(CH}_3\text{)}_3\text{CBr} \rightarrow \text{(CH}_3\text{)}_3\text{C}^+ + \text{Br}^- \).
Step 3: The carbocation formed is stabilized by the inductive and hyperconjugative effects of the three methyl groups. The nucleophiles present in the solvent mixture (ethanol and water) can now attack the carbocation. Ethanol (\( \text{CH}_3\text{CH}_2\text{OH} \)) and water (\( \text{H}_2\text{O} \)) are both nucleophiles, and they will form substitution products by bonding to the carbocation.
Step 4: The substitution products formed are tert-butyl ethyl ether (\( \text{(CH}_3\text{)}_3\text{COCH}_2\text{CH}_3 \)) when ethanol acts as the nucleophile, and tert-butyl alcohol (\( \text{(CH}_3\text{)}_3\text{COH} \)) when water acts as the nucleophile. These are the major products of the reaction.
Step 5: For part b, the same products are obtained with 2-chloro-2-methylpropane because it is also a tertiary alkyl halide. The SN1 mechanism is favored in both cases due to the stability of the carbocation intermediate and the polar protic solvent mixture. The only difference is the leaving group (Cl⁻ vs. Br⁻), but both are good leaving groups, so the reaction proceeds similarly.
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Nucleophilic Substitution Reactions
Nucleophilic substitution reactions involve the replacement of a leaving group in a molecule by a nucleophile. In the case of 2-bromo-2-methylpropane and 2-chloro-2-methylpropane, the nucleophile is the solvent mixture of ethanol and water. The reaction can proceed via either the SN1 or SN2 mechanism, depending on the substrate structure and reaction conditions.
Video consigliato:
01:47
Nucleophiles and Electrophiles can react in Substitution Reactions.
SN1 vs. SN2 Mechanisms
The SN1 mechanism is a two-step process where the leaving group departs first, forming a carbocation intermediate, followed by nucleophilic attack. In contrast, the SN2 mechanism is a one-step process where the nucleophile attacks the substrate simultaneously as the leaving group departs. The structure of 2-bromo-2-methylpropane and 2-chloro-2-methylpropane favors the SN1 pathway due to steric hindrance, leading to similar products.
Video consigliato:
10:49Drawing the SN1 Mechanism
Solvent Effects on Reaction Pathways
The choice of solvent can significantly influence the pathway of nucleophilic substitution reactions. A polar protic solvent, like the ethanol-water mixture, stabilizes carbocations and promotes the SN1 mechanism. This stabilization allows for the formation of similar substitution products from both 2-bromo-2-methylpropane and 2-chloro-2-methylpropane, as the solvent facilitates the reaction by solvating the ions formed during the process.
Video consigliato:
02:26General format of reactions and how to interpret solvents.
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