Textbook Question
Of the compounds you named in Problem 45:
b. Which is the least stable?
a.
b.
c.
d.
e.
f.
820
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Ch. 5 - Alkenes: Structure, Nomenclature, and an Introduction to Reactivity • Thermodynamics and Kinetics
Bruice8th EditionOrganic ChemistryISBN: 9780135213711
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Table of contents
- Ch. 1 - Remembering General Chemistry: Electronic Structure and Bonding (Part 1)31
- Ch. 1 - Remembering General Chemistry: Electronic Structure and Bonding (Part 2)65
- Ch. 2 - Acids and Bases: Central to Understanding Organic Chemistry84
- Ch. 3 - An Introduction to Organic Compounds:Nomenclature, Physical Properties, and Structure183
- Ch. 4 - Isomers: The Arrangement of Atoms in Space121
- Ch. 5 - Alkenes: Structure, Nomenclature, and an Introduction to Reactivity • Thermodynamics and Kinetics83
- Ch. 6 - The Reactions of Alkenes • The Stereochemistry of Addition Reactions175
- Ch. 7 - The Reactions of Alkynes • An Introduction to Multistep Synthesis119
- Ch. 8 - Delocalized Electrons: Their Effect on Stability, pKa, and the Products of a Reaction • Aromaticity and Electronic Effects: An Introduction to the Reactions of Benzene148
- Ch. 9 - Substitution and Elimination Reactions of Alkyl Halides212
- Ch. 10 - Reactions of Alcohols, Ethers, Epoxides, Amines, and Sulfur-Containing Compounds131
- Ch. 11 - Organometallic Compounds60
- Ch. 12 - Radicals90
- Ch. 13 - Mass Spectrometry; Infrared Spectroscopy; UV/Vis Spectroscopy62
- Ch. 14 - NMR Spectroscopy95
- Ch. 15 - Reactions of Carboxylic Acids and Carboxylic Acid Derivatives123
- Ch. 16 - Reactions of Aldehydes and Ketones • More Reactions of Carboxylic Acid Derivatives141
- Ch. 17 - Reactions at the Alpha-Carbon101
- Ch. 18 - Reactions of Benzene and Substituted Benzenes144
- Ch. 19 - More About Amines • Reactions of Heterocyclic Compounds49
- Ch. 20 - The Organic Chemistry of Carbohydrates80
- Ch. 21 - Amino Acids, Peptides, and Proteins57
- Ch. 22 - Catalysis in Organic Reactions and in Enzymatic Reactions35
- Ch. 23 - The Organic Chemistry of the Coenzymes—Compounds Derived from Vitamins1
- Ch. 28 - Pericyclic Reactions58
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Bruice 8th EditionCh. 5 - Alkenes: Structure, Nomenclature, and an Introduction to Reactivity • Thermodynamics and KineticsProblem 47
Bruice 8th EditionCh. 5 - Alkenes: Structure, Nomenclature, and an Introduction to Reactivity • Thermodynamics and KineticsProblem 47Chapter 6, Problem 47
a. Which is the most stable: 3,4-dimethyl-2-hexene, 2,3-dimethyl-2-hexene, or 4,5-dimethyl-2-hexene?
b. Which compound has the largest heat of hydrogenation?
c. Which compound has the smallest heat of hydrogenation?
Verified step by step guidance1
Step 1: Understand the stability of alkenes. Alkene stability is influenced by the degree of substitution of the double bond. More substituted alkenes are generally more stable due to hyperconjugation and inductive effects. Tetrasubstituted alkenes are the most stable, followed by trisubstituted, disubstituted, and monosubstituted alkenes.
Step 2: Analyze the substitution pattern of each compound. For 3,4-dimethyl-2-hexene, the double bond is between carbons 2 and 3, and it is trisubstituted. For 2,3-dimethyl-2-hexene, the double bond is between carbons 2 and 3, and it is tetrasubstituted. For 4,5-dimethyl-2-hexene, the double bond is between carbons 2 and 3, and it is disubstituted.
Step 3: Compare the stability of the compounds. Based on the substitution pattern, 2,3-dimethyl-2-hexene (tetrasubstituted) is the most stable, followed by 3,4-dimethyl-2-hexene (trisubstituted), and then 4,5-dimethyl-2-hexene (disubstituted).
Step 4: Understand the relationship between heat of hydrogenation and stability. The heat of hydrogenation is inversely related to alkene stability. More stable alkenes release less heat upon hydrogenation, while less stable alkenes release more heat.
Step 5: Determine the compounds with the largest and smallest heat of hydrogenation. The least stable compound, 4,5-dimethyl-2-hexene, will have the largest heat of hydrogenation. The most stable compound, 2,3-dimethyl-2-hexene, will have the smallest heat of hydrogenation.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Stability of Alkenes
The stability of alkenes is influenced by the degree of substitution at the double bond. More substituted alkenes, such as tetrasubstituted or trisubstituted, are generally more stable due to hyperconjugation and the inductive effect of alkyl groups. In this context, comparing the substitution patterns of 3,4-dimethyl-2-hexene, 2,3-dimethyl-2-hexene, and 4,5-dimethyl-2-hexene will help determine which is the most stable.
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04:28
Understanding trends of alkene stability.
Heat of Hydrogenation
The heat of hydrogenation is a measure of the energy released when an alkene is converted to an alkane through the addition of hydrogen. A higher heat of hydrogenation indicates a less stable alkene, as more energy is required to break the double bond. Thus, analyzing the heats of hydrogenation for the given compounds will reveal which has the largest and smallest values, correlating with their stability.
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00:48The definition of hydrogenation.
Zaitsev's Rule
Zaitsev's Rule states that in elimination reactions, the more substituted alkene is typically the major product. This principle can be applied to predict the stability of the alkenes formed from the compounds in the question. Understanding this rule aids in determining which compound will have a lower heat of hydrogenation due to its greater stability, as more substituted alkenes are favored.
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01:18Defining Zaitsev’s Rule
Related Practice
Textbook Question
Of the compounds you named in Problem 45:
a. Which is the most stable?
a.
b.
c.
d.
e.
f.
788
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Textbook Question
Name the following:
d.
e.
f.
1152
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Textbook Question
Draw the skeletal structure of 3,3-dimethyl-7-(1-methylethyl)-6-(1-methylpropyl)decane.
1252
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Textbook Question
In a reaction in which reactant A is in equilibrium with product B at 25 °C, what relative amounts of A and B are present at equilibrium if ∆G° at 25 °C is
a. 2.72 kcal/mol?
b. 0.65 kcal/mol?
1178
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Textbook Question
In a reaction in which reactant A is in equilibrium with product B at 25 °C, what relative amounts of A and B are present at equilibrium if ∆G° at 25 °C is
c. -2.72 kcal/mol?
d. -0.65 kcal/mol?
849
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