Textbook Question
Show the product of the Diels–Alder dimerization of cyclobutadiene. (This reaction is similar to the dimerization of cyclopentadiene, discussed in Section 15-11.)
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Ch. 16 - Aromatic Compounds
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 16, Problem 2b
Using the information in Figure 16-2, calculate the values of ∆H° for the following reactions:
(b) 
Verified step by step guidance1
Step 1: Identify the reaction. The given reaction involves the hydrogenation of benzene (C₆H₆) with 2 moles of hydrogen gas (H₂) in the presence of a catalyst to form cyclohexene (C₆H₁₀).
Step 2: Refer to Figure 16-2 for the enthalpy values. Look for the standard enthalpy of formation (∆H°f) values for benzene (C₆H₆), hydrogen gas (H₂), and cyclohexene (C₆H₁₀). These values are typically provided in a table or graph in the figure.
Step 3: Write the equation for calculating ∆H° for the reaction. Use the formula: ∆H° = Σ∆H°f(products) - Σ∆H°f(reactants).
Step 4: Substitute the values into the equation. For the products, use the ∆H°f value of cyclohexene. For the reactants, sum the ∆H°f values of benzene and 2 moles of hydrogen gas (note that the ∆H°f of H₂ gas is usually 0).
Step 5: Perform the subtraction to determine the ∆H° for the reaction. Ensure that the units are consistent (typically kJ/mol) and interpret the sign of ∆H° (negative for exothermic reactions, positive for endothermic reactions).
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Enthalpy Change (∆H°)
Enthalpy change (∆H°) is a measure of the heat content of a system at constant pressure. It indicates whether a reaction is exothermic (releases heat, ∆H° < 0) or endothermic (absorbs heat, ∆H° > 0). Calculating ∆H° for a reaction involves using standard enthalpy values of formation for the reactants and products, allowing chemists to predict the energy changes associated with chemical reactions.
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Calculating Enthalpies
Catalysis
Catalysis refers to the process of increasing the rate of a chemical reaction by adding a substance known as a catalyst. Catalysts work by providing an alternative reaction pathway with a lower activation energy, thus facilitating the conversion of reactants to products without being consumed in the process. In the given reaction, a catalyst is necessary to hydrogenate benzene into cyclohexane efficiently.
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Hydrogenation of Aromatic Compounds
Hydrogenation of aromatic compounds involves the addition of hydrogen (H2) to the aromatic ring, converting it into a saturated compound. This reaction typically requires a catalyst, such as palladium or platinum, to proceed under mild conditions. In this case, benzene is being hydrogenated to form cyclohexane, which is a key transformation in organic synthesis and industrial applications.
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Related Practice
Textbook Question
a. Draw the resonance forms of benzene, cyclobutadiene, and cyclooctatetraene, showing all the carbon and hydrogen atoms.
b. Assuming that these molecules are all planar, show how the p orbitals on the sp2 hybrid carbon atoms form continuous rings of overlapping orbitals above and below the plane of the carbon atoms.
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Textbook Question
Using the information in Figure 16-2, calculate the values of ∆H° for the following reactions:
(a)
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Textbook Question
Using the information in Figure 16-2, calculate the values of ∆H° for the following reactions:
(c)
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