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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
Bruice - Organic Chemistry 8th Edition
Bruice8th EditionOrganic ChemistryISBN: 9780135213711Not the one you use?Change textbook
All textbooksBruice 8th EditionCh. 8 - Delocalized Electrons: Their Effect on Stability, pKa, and the Products of a Reaction • Aromaticity and Electronic Effects: An Introduction to the Reactions of BenzeneProblem 20a,b,c
Chapter 9, Problem 20a,b,c

For each of the following substituents, indicate whether it withdraws electrons inductively, donates electrons by hyperconjugation, withdraws electrons by resonance, or donates electrons by resonance.
a. Br
b. CH2CH3
c. Chemical structure of a carbonyl group with a methyl group, illustrating concepts of acidity and electron effects.

Verified step by step guidance
1
Identify the substituent in question and determine its electronic properties based on its structure. For example, look for electronegative atoms, lone pairs, or π-bonds that can participate in resonance or hyperconjugation.
To determine if the substituent withdraws electrons inductively, check if it contains electronegative atoms (e.g., halogens, oxygen, or nitrogen) or groups that pull electron density through sigma bonds due to their electronegativity.
To determine if the substituent donates electrons by hyperconjugation, look for alkyl groups or groups with C-H bonds adjacent to a positively charged or electron-deficient center. Hyperconjugation involves the delocalization of electrons from these C-H bonds.
To determine if the substituent withdraws electrons by resonance, check if it has a π-system (e.g., carbonyl groups, nitro groups) that can delocalize electron density away from the rest of the molecule through resonance.
To determine if the substituent donates electrons by resonance, look for groups with lone pairs (e.g., -OH, -OR, -NH2) that can delocalize electron density into a conjugated π-system or aromatic ring through resonance.

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Key Concepts

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

Inductive Effect

The inductive effect refers to the permanent polarization of a bond due to the electronegativity difference between atoms. Electronegative atoms or groups can withdraw electron density from adjacent atoms, leading to a decrease in electron density in the molecule. This effect diminishes with distance and is crucial for understanding how substituents influence the reactivity and stability of organic compounds.
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Resonance Effect

The resonance effect involves the delocalization of electrons across multiple atoms in a molecule, which can stabilize the structure. Electron-donating groups can provide electron density through resonance, while electron-withdrawing groups can pull electron density away. Understanding resonance is essential for predicting the behavior of substituents in reactions and their impact on molecular stability.
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Hyperconjugation

Hyperconjugation is a stabilizing interaction that occurs when the electrons in a sigma bond (usually C-H or C-C) interact with an adjacent empty or partially filled p-orbital or π-bond. This effect can lead to electron donation, enhancing the stability of carbocations or alkenes. Recognizing hyperconjugation is important for analyzing the stability of intermediates in organic reactions.
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Related Practice
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?

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Textbook Question

Which member of each pair is the stronger base?

a. ethylamine or aniline

b. ethylamine or ethoxide ion

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Textbook Question

For each of the following substituents, indicate whether it withdraws electrons inductively, donates electrons by hyperconjugation, withdraws electrons by resonance, or donates electrons by resonance.

d. NHCH3

e. OCH3

f. +N(CH3)3

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Textbook Question

Which acid in each of the following pairs is stronger?

e.

f.

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Textbook Question

Which acid in each of the following pairs is stronger?

c.

d.

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Textbook Question

Which member of each pair is the stronger base?

c. phenolate ion or ethoxide ion

d. phenolate ion or acetate ion

1
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