Textbook Question
Show how you would convert
a. oct-3-yne to cis-oct-3-ene.
b. pent-2-yne to trans-pent-2-ene.
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Ch.9 - Alkynes
Wade9th EditionOrganic ChemistryISBN: 9780135213728
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Table of contents
- Ch.1 - Structure and Bonding107
- Ch. 2 - Acids and Bases; Functional Groups115
- Ch.3 - Structure and Stereochemistry of Alkanes100
- Ch.4 - The Study of Chemical Reactions99
- Ch.5 - Stereochemistry93
- Ch.6 - Alkyl Halides; Nucleophilic Substitution118
- Ch. 7 - Structure and Synthesis of Alkenes; Elimination158
- Ch.8 - Reactions of Alkenes171
- Ch.9 - Alkynes91
- Ch.10 - Structure and Synthesis of Alcohols143
- Ch.11 - Reactions of Alcohols104
- Ch. 12 - Infrared Spectroscopy and Mass Spectrometry22
- Ch. 13 - Nuclear Magnetic Resonance Spectroscopy45
- Ch. 14 - Ethers, Epoxides, and Thioethers72
- Ch. 15 - Conjugated Systems, Orbital Symmetry, and Ultraviolet Spectroscopy89
- Ch. 16 - Aromatic Compounds74
- Ch. 17 - Reactions of Aromatic Compounds126
- Ch. 18 - Ketones and Aldehydes193
- Ch. 19 - Amines129
- Ch. 20 - Carboxylic Acids77
- Ch. 21 - Carboxylic Acid Derivatives141
- Ch. 22 - Condensations and Alpha Substitutions of Carbonyl Compounds175
- Ch. 23 - Carbohydrates and Nucleic Acids93
- Ch. 24 - Amino Acids, Peptides, and Proteins54
Chapter 9, Problem 11
When 2,2-dibromo-1-phenylpropane is heated overnight with sodium amide at 150°C, the major product (after addition of water) is a different foul-smelling compound of formula C9H8. Propose a structure for this product, and give a mechanism to account for its formation.
Verified step by step guidance1
Identify the starting material: The compound 2,2-dibromo-1-phenylpropane has a phenyl group (C6H5-) attached to a propane chain with two bromine atoms on the same carbon (C2). Its structure is: C6H5-CH(CBr2)-CH3.
Analyze the reaction conditions: Sodium amide (NaNH2) is a strong base and nucleophile, and heating at 150 °C suggests an elimination reaction. The addition of water at the end indicates that the reaction involves deprotonation and possibly the formation of a reactive intermediate.
Propose the mechanism: Sodium amide abstracts a proton from the methyl group (CH3) adjacent to the dibromo carbon, forming a carbanion. This carbanion undergoes elimination of two bromine atoms (via two successive E2 eliminations), leading to the formation of a triple bond (alkyne) between the two carbons.
Determine the product structure: After the elimination of HBr twice, the resulting compound is phenylacetylene (C6H5-C≡CH), which matches the molecular formula C9H8. This compound is known to have a foul smell.
Summarize the mechanism: The reaction proceeds via a double dehydrohalogenation mechanism (E2 elimination) facilitated by the strong base (NaNH2), followed by the addition of water to neutralize any remaining reactive intermediates, yielding phenylacetylene as the final product.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Elimination Reactions
Elimination reactions involve the removal of atoms or groups from a molecule, resulting in the formation of a double bond. In the context of heating 2,2-dibromo-1-phenylpropane with sodium amide, a dehydrohalogenation process occurs, where bromine atoms are eliminated, leading to the formation of an alkene. Understanding this mechanism is crucial for predicting the structure of the final product.
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00:40
Recognizing Elimination Reactions.
Nucleophilic Substitution
Nucleophilic substitution is a fundamental reaction in organic chemistry where a nucleophile replaces a leaving group in a molecule. In this case, sodium amide acts as a strong nucleophile, facilitating the substitution of bromine atoms in 2,2-dibromo-1-phenylpropane. This concept is essential for understanding how the initial compound transforms into the foul-smelling product.
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01:47Nucleophiles and Electrophiles can react in Substitution Reactions.
Aromatic Compounds
Aromatic compounds are cyclic structures that follow Huckel's rule, exhibiting resonance and stability due to delocalized pi electrons. The product of the reaction is likely to contain an aromatic ring, which contributes to its distinct properties, including its foul smell. Recognizing the role of aromaticity helps in predicting the characteristics and stability of the final compound formed from the reaction.
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08:19Intro to Aromaticity
Related Practice
Textbook Question
When 2,2-dibromo-1-phenylpropane is heated overnight in fused KOH at 200 C, the major product is a foul-smelling compound of formula C9H8. Propose a structure for this product, and give a mechanism to account for its formation.
Problem-Solving Hint:
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Textbook Question
Show how you would synthesize each compound, beginning with acetylene and any necessary additional reagents
(c)
(d)
655
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Textbook Question
Show how you would convert
c. cis-cyclodecene to trans-cyclodecene.
1223
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Textbook Question
Show how you would convert
d. but-1-yne to cis-hex-3-ene.
1166
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Textbook Question
Show how you would synthesize 2-phenylhex-3-yn-2-ol, starting with acetophenone (PhCOCH3) and any other reagents you need. ("2-ol" means there is an OH group on C2.)
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