Table of contents

1. A Review of General Chemistry5h 5m
2. Molecular Representations1h 14m
3. Acids and Bases2h 46m
4. Alkanes and Cycloalkanes4h 17m
5. Chirality3h 39m
6. Thermodynamics and Kinetics1h 22m
7. Substitution Reactions1h 48m
8. Elimination Reactions2h 30m
9. Alkenes and Alkynes2h 9m
10. Addition Reactions3h 19m
11. Radical Reactions1h 58m
12. Alcohols, Ethers, Epoxides and Thiols2h 42m
13. Alcohols and Carbonyl Compounds2h 17m
14. Synthetic Techniques1h 26m
15. Analytical Techniques:IR, NMR, Mass Spect7h 3m
16. Conjugated Systems6h 13m
17. Ultraviolet Spectroscopy51m
18. Aromaticity2h 34m
19. Reactions of Aromatics: EAS and Beyond5h 1m
20. Phenols55m
21. Aldehydes and Ketones: Nucleophilic Addition4h 56m
22. Carboxylic Acid Derivatives: NAS2h 51m
23. The Chemistry of Thioesters, Phophate Ester and Phosphate Anhydrides1h 10m
24. Enolate Chemistry: Reactions at the Alpha-Carbon1h 53m
25. Condensation Chemistry2h 9m
26. Amines1h 43m
27. Heterocycles2h 0m
28. Carbohydrates5h 53m
29. Amino Acids4h 20m
30. Peptides and Proteins2h 42m
31. Catalysis in Organic Reactions1h 30m
32. Lipids 2h 50m
33. The Organic Chemistry of Metabolic Pathways2h 52m
34. Nucleic Acids1h 32m
35. Transition Metals6h 14m
36. Synthetic Polymers1h 49m

19. Reactions of Aromatics: EAS and Beyond

Electron Withdrawing Groups

Organic Chemistry

19. Reactions of Aromatics: EAS and Beyond

Electron Withdrawing Groups

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Problem 31

Textbook Question

Substitution at the benzylic position of the molecules shown was observed to occur at different rates. Explain this observation.

Verified step by step guidance

Identify the benzylic position in the molecules. The benzylic position is the carbon atom directly attached to a benzene ring. This position is often reactive due to the resonance stabilization provided by the benzene ring.

Analyze the substituents on the benzene ring and the benzylic carbon. Substituents can influence the reactivity of the benzylic position through electronic effects (inductive or resonance effects). Electron-donating groups (EDGs) and electron-withdrawing groups (EWGs) play a key role here.

Consider the stability of the intermediate formed during the substitution reaction. For example, in an SN1 reaction, the formation of a benzylic carbocation intermediate is stabilized by resonance with the benzene ring. Substituents that stabilize or destabilize this intermediate will affect the reaction rate.

Evaluate steric effects. Bulky substituents near the benzylic position can hinder the approach of the nucleophile, slowing down the reaction. Conversely, less steric hindrance allows for faster substitution.

Compare the molecules based on the above factors (electronic effects, intermediate stability, and steric effects) to explain why substitution occurs at different rates. For example, a molecule with an electron-donating group at the para position may stabilize the benzylic carbocation more effectively, leading to a faster reaction rate.

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Key Concepts

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

Benzylic Position

The benzylic position refers to the carbon atom directly attached to a benzene ring. This position is significant in organic chemistry because it often exhibits unique reactivity due to the resonance stabilization provided by the aromatic system. Substitutions at this position can be influenced by the electronic effects of substituents on the benzene ring, affecting the rate of reaction.

Substitution Reactions

Substitution reactions involve the replacement of one atom or group in a molecule with another. In the context of benzylic substitution, these reactions can occur via mechanisms such as nucleophilic substitution (SN1 or SN2) or electrophilic substitution. The rate of substitution can vary based on factors like sterics, electronics, and the nature of the leaving group.

Resonance and Stability

Resonance is a concept that describes the delocalization of electrons in a molecule, which can stabilize certain intermediates during chemical reactions. In benzylic substitution, the stability of the carbocation intermediate formed during the reaction can significantly influence the reaction rate. More stable intermediates lead to faster reactions, explaining the observed differences in substitution rates.

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Related Practice

Textbook Question

For each horizontal row of substituted benzenes, indicate

c. the one that yields the highest percentage of meta product in an electrophilic aromatic substitution reaction.

Textbook Question

Why is anisole nitrated more rapidly than thioanisole under the same conditions?

Textbook Question

A mixture of 0.10 mol benzene and 0.10 mol p-xylene was allowed to react with 0.10 mol nitronium ion until all the nitronium ion was gone. Two products were obtained: 0.002 mol of one and 0.098 mol of the other.

b. Why was more of one product obtained than of the other?

Textbook Question

Indigo is a dye that was originally isolated from coal tar. In 1905, Johann Friedrich Wilhelm Adolf von Baeyer won a Nobel Prize for a method that allowed indigo to be isolated from plants [a green chemist ahead of his time.] If you nitrated indigo using the reaction learned in this chapter, at which carbon would you expect the nitro group to attach?

Textbook Question

Which of the following phenoxides should be a stronger nucleophile?

Textbook Question

Predict the mononitration products of the following compounds.

d. p-methoxybenzoic acid

Textbook Question

Predict the mononitration products of the following compounds.

e. m-cresol (m-methylphenol)

Textbook Question

Predict the mononitration products of the following compounds.

f. o-hydroxyacetophenone

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