Textbook Question
For each molecular formula, draw all the isomeric alkynes, and give their IUPAC names. Circle the acetylenic hydrogen of each terminal alkyne.
(a) C5H8 (three isomers)
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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 1
Draw structural formulas of at least two alkynes of each molecular formula.
1. C6H10
2. C8H12
3. C7H8
Verified step by step guidance1
Step 1: Understand the general formula for alkynes, which is CnH2n-2. This will help you determine if the given molecular formulas can represent alkynes.
Step 2: For C6H10, verify that it fits the alkyne formula CnH2n-2. Here, n=6, so 2n-2=10, which matches. Now, draw possible structures. Start with a straight chain alkyne, such as hex-1-yne, and then consider branching, like 3-methylpent-1-yne.
Step 3: For C8H12, check if it fits the alkyne formula. Here, n=8, so 2n-2=14, which does not match. This means C8H12 cannot be a simple alkyne. Consider cyclic structures or multiple bonds to satisfy the formula.
Step 4: For C7H8, check if it fits the alkyne formula. Here, n=7, so 2n-2=12, which does not match. C7H8 is more likely to be an aromatic compound like toluene, rather than an alkyne.
Step 5: For each valid molecular formula, draw at least two structural isomers. Ensure that each structure adheres to the rules of valency and the alkyne's triple bond characteristics. Use line-angle formulas for clarity.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Alkyne Structure
Alkynes are hydrocarbons that contain at least one carbon-carbon triple bond, denoted as C≡C. This triple bond is a defining feature, giving alkynes their unique properties. The simplest alkyne is ethyne (acetylene), and the presence of the triple bond affects the molecule's geometry, making it linear around the bond.
Molecular Formula and Degree of Unsaturation
The molecular formula provides the number of each type of atom in a molecule. For alkynes, the degree of unsaturation helps determine the number of rings and/or multiple bonds. Each triple bond contributes two degrees of unsaturation, which is crucial for deducing possible structures from a given formula.
Isomerism in Alkynes
Isomerism refers to compounds with the same molecular formula but different structures. In alkynes, structural isomers can arise from variations in the position of the triple bond or branching of the carbon chain. Understanding isomerism is essential for drawing different structural formulas for a given molecular formula.
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