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 12d
Show how you would convert
d. but-1-yne to cis-hex-3-ene.
Verified step by step guidance1
Step 1: Begin by identifying the functional group in but-1-yne. It contains a terminal alkyne group (-C≡C-H). The goal is to extend the carbon chain and convert the alkyne into a cis-alkene.
Step 2: Perform a hydroboration reaction to add a boron atom to the terminal alkyne. Use a reagent like disiamylborane (R2BH) to selectively add boron to the terminal carbon. This step prepares the molecule for further functionalization.
Step 3: Oxidize the boron intermediate using hydrogen peroxide (H2O2) in a basic solution (NaOH). This converts the boron group into an alcohol (-OH) at the terminal carbon, resulting in an aldehyde (butanal).
Step 4: Perform a Wittig reaction to extend the carbon chain. React the aldehyde with a phosphonium ylide (Ph3P=CHCH2CH3) to form hex-3-yne. This reaction adds three carbons to the molecule and introduces a triple bond at the desired position.
Step 5: Hydrogenate hex-3-yne using a Lindlar catalyst (Pd/CaCO3, poisoned with quinoline) to selectively reduce the triple bond to a cis-double bond, yielding cis-hex-3-ene 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.
Alkyne to Alkene Conversion
The conversion of alkynes to alkenes typically involves a reaction known as hydrogenation, where hydrogen gas is added across the triple bond of the alkyne. This process can be facilitated by catalysts such as palladium or platinum, which help to break the triple bond and form a double bond, resulting in an alkene. In this case, but-1-yne will be transformed into an alkene intermediate before further reactions can yield the desired product.
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How to name alkenes and alkynes
Stereochemistry and Cis-Trans Isomerism
Cis-trans isomerism is a form of stereoisomerism where the spatial arrangement of groups around a double bond affects the properties of the molecule. In cis isomers, similar groups are on the same side of the double bond, while in trans isomers, they are on opposite sides. Understanding this concept is crucial for converting the alkene intermediate into cis-hex-3-ene, as the reaction conditions must favor the formation of the cis isomer.
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Reagents for Stereoselective Reactions
To achieve the specific stereochemistry required for cis-hex-3-ene, certain reagents and conditions must be employed. For example, the use of specific catalysts or reagents that promote syn-addition during the hydrogenation process can lead to the formation of the cis isomer. Familiarity with these reagents and their mechanisms is essential for successfully directing the reaction towards the desired stereochemical outcome.
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Related Practice
Textbook Question
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.
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Textbook Question
Show how you would convert
c. cis-cyclodecene to trans-cyclodecene.
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Textbook Question
Propose a mechanism for the entire reaction of pent-1-yne with 2 moles of HBr. Show why Markovnikov's rule should be observed in both the first and second additions of HBr.
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Textbook Question
The fragrance of (Z)-1-phenylhex-2-en-1-ol resembles that of roses, with a delicate citrus edge. Show how you would synthesize this compound from benzaldehyde (PhCHO) and any other reagents you need.
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Textbook Question
In the addition of just 1 mole of bromine to 1 mole of hex-1-yne, should the hex-1-yne be added to a bromine solution or should the bromine be added to the hex-1-yne? Explain your answer.
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