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 Benzene

Bruice8th EditionOrganic ChemistryISBN: 9780135213711Not the one you use?Change textbook

Bruice 8th Edition

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 Benzene

Problem 12

Chapter 9, Problem 12

Name the following dienes and rank them from most stable to least stable.

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Identify the structure of each diene in the image. Look for the presence of conjugated double bonds, isolated double bonds, or cumulated double bonds.

Apply the IUPAC naming rules to each diene. Start by identifying the longest carbon chain that includes both double bonds, and number the chain starting from the end closest to the first double bond.

Determine the position of each double bond in the chain and use the appropriate locants in the name. Remember to use the suffix '-diene' to indicate the presence of two double bonds.

Evaluate the stability of each diene. Conjugated dienes (where double bonds are separated by a single bond) are generally more stable than isolated dienes (where double bonds are separated by more than one single bond) and cumulated dienes (where double bonds are adjacent).

Rank the dienes from most stable to least stable based on their structure. Conjugated dienes are typically the most stable due to resonance stabilization, followed by isolated dienes, and cumulated dienes are usually the least stable.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Diene Stability

Diene stability refers to the relative stability of compounds containing two double bonds. Factors influencing this stability include the degree of substitution on the double bonds, with more substituted dienes generally being more stable due to hyperconjugation and the inductive effect. Additionally, the presence of conjugation, where double bonds are separated by a single bond, can enhance stability through resonance.

Conjugation

Conjugation occurs when alternating single and double bonds allow for the delocalization of π electrons across the molecule. This delocalization stabilizes the molecule, making conjugated dienes more stable than isolated double bonds. The stability from conjugation is a key factor when ranking the stability of different diene structures.

Substitution Patterns

The substitution pattern of a diene significantly affects its stability. Dienes can be classified as 1,2-disubstituted, 1,3-disubstituted, or unsubstituted, with 1,3-disubstituted dienes typically being the most stable due to increased hyperconjugation and steric effects. Understanding these patterns is essential for accurately ranking the stability of the given dienes.

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Related Practice

Textbook Question

Answer the following questions for the MOs of 1,3-butadiene:

a. Which are $π$ bonding MOs, and which are $π$ * antibonding MOs?

b. Which MOs are symmetric, and which are antisymmetric?

c. Which MO is the HOMO and which is the LUMO in the ground state?

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Textbook Question

a. Draw resonance contributors for the following species. Do not include structures that are so unstable that their contributions to the resonance hybrid would be negligible. Indicate which are major contributors and which are minor contributors to the resonance hybrid.

b. Do any of the species have resonance contributors that all contribute equally to the resonance hybrid?

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Textbook Question

What is the total number of nodes in the $ψ$ ₃ and $ψ$ ₄ MOs of 1,3-butadiene?

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Textbook Question

Answer the following questions for the MOs of 1,3-butadiene:

d. Which MO is the HOMO and which is the LUMO in the excited state?

e. What is the relationship between the HOMO and the LUMO and symmetric and antisymmetric orbitals?