Textbook Question
Show how you would convert (in one or two steps) 1-phenylpropane to the three products shown below. In each case, explain what unwanted reactions might produce undesirable impurities in the product.
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Ch. 7 - Structure and Synthesis of Alkenes; Elimination
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 7, Problem 58c
Show how you would convert (in one or two steps) 1-phenylpropane to the three products shown below. In each case, explain what unwanted reactions might produce undesirable impurities in the product.
Verified step by step guidance1
Step 1: To convert 1-phenylpropane to 1-phenylprop-1-ene, perform a dehydrogenation reaction. This can be achieved using a strong base such as potassium tert-butoxide (KOtBu) in the presence of heat. The base abstracts a proton from the β-carbon, leading to the formation of the double bond between the α and β carbons.
Step 2: Consider potential side reactions. Unwanted reactions might include over-dehydrogenation, leading to the formation of conjugated dienes or other byproducts. To minimize these, control the reaction conditions carefully, such as temperature and base concentration.
Step 3: Analyze the stereochemistry of the product. The reaction may produce both E and Z isomers of 1-phenylprop-1-ene. Separation or purification techniques, such as distillation or chromatography, may be required to isolate the desired isomer.
Step 4: Ensure the reaction is selective for the desired product. Using sterically hindered bases like KOtBu can help favor the formation of the desired alkene while minimizing side reactions.
Step 5: Confirm the product structure using spectroscopic techniques such as NMR or IR spectroscopy to ensure the formation of 1-phenylprop-1-ene and check for impurities.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Alkene Formation
Alkene formation involves the elimination of a small molecule, typically water or hydrogen halide, from an alkane or alcohol, resulting in a double bond. In the case of converting 1-phenylpropane to 1-phenylprop-1-ene, a dehydration or dehydrohalogenation reaction can be employed. Understanding the conditions and reagents that favor this transformation is crucial for achieving the desired product.
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Rearrangement Reactions
Rearrangement reactions occur when the structure of a molecule changes to form a more stable isomer. In organic synthesis, these reactions can lead to unwanted products if the reaction conditions favor rearrangement over the desired pathway. Recognizing potential rearrangements is essential to minimize impurities and ensure the selectivity of the reaction.
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Side Reactions and Impurities
Side reactions are unintended reactions that can occur alongside the desired reaction, leading to the formation of impurities. These can arise from various factors, including the presence of reactive intermediates or inappropriate reaction conditions. Identifying and controlling these side reactions is vital for purifying the final product and achieving high yields of the desired compound.
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Related Practice
Textbook Question
Show how you would prepare cyclopentene from each compound.
c. cyclopentane (not by dehydrogenation)
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Textbook Question
Propose mechanisms for the following reactions. Additional products may be formed, but your mechanism only needs to explain the products shown.
(a)
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Textbook Question
Propose mechanisms for the following reactions. Additional products may be formed, but your mechanism only needs to explain the products shown.
(b)
1
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Textbook Question
Show how you would convert (in one or two steps) 1-phenylpropane to the three products shown below. In each case, explain what unwanted reactions might produce undesirable impurities in the product.
6
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Textbook Question
E1 eliminations of alkyl halides are rarely useful for synthetic purposes because they give mixtures of substitution and elimination products. Explain why the sulfuric acid-catalyzed dehydration of cyclohexanol gives a good yield of cyclohexene even though the reaction goes by an E1 mechanism. (Hint: What are the nucleophiles in the reaction mixture? What products are formed if these nucleophiles attack the carbocation? What further reactions can these substitution products undergo?)
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