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

1. A Review of General Chemistry

Resonance Structures

Organic Chemistry

1. A Review of General Chemistry

Resonance Structures

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5:22 minutes

Problem 41b(i,ii)

Textbook Question

Allylic halides have the structure

b. Draw the resonance structures of the allylic cations formed by ionization of the following halides.
(i)
(ii)

Verified step by step guidance

Identify the allylic position in the given halides. The allylic position is the carbon atom adjacent to the carbon-carbon double bond.

For compound (i), remove the bromine atom to form a carbocation at the allylic position. This will result in a positive charge on the carbon atom adjacent to the double bond.

Draw the first resonance structure for compound (i) by moving the pi electrons from the double bond to form a new double bond with the carbocation, shifting the positive charge to the other end of the original double bond.

For compound (ii), similarly, remove the bromine atom to form a carbocation at the allylic position, resulting in a positive charge on the carbon atom adjacent to the double bond.

Draw the first resonance structure for compound (ii) by moving the pi electrons from the double bond to form a new double bond with the carbocation, shifting the positive charge to the other end of the original double bond.

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Key Concepts

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

Allylic Halides

Allylic halides are organic compounds where a halogen atom is bonded to a carbon atom adjacent to a carbon-carbon double bond. This structure allows for unique reactivity due to the presence of the double bond, which can stabilize intermediates through resonance. The allylic position is particularly reactive in substitution and elimination reactions.

Resonance Structures

Resonance structures are different Lewis structures for a molecule that depict the same arrangement of atoms but differ in the distribution of electrons. They are used to represent the delocalization of electrons within a molecule, which can stabilize charged intermediates like allylic cations. Resonance structures are crucial for understanding the stability and reactivity of organic compounds.

Allylic Cations

Allylic cations are positively charged intermediates formed when a halide ion leaves an allylic halide, resulting in a carbocation at the allylic position. These cations are stabilized by resonance, as the positive charge can be delocalized over the adjacent double bond. This delocalization makes allylic cations more stable than typical carbocations, influencing their reactivity in chemical reactions.

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Draw the important resonance forms of the following free radicals.

(c)

(d)

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Draw the important resonance forms of the following free radicals.

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Draw the important resonance forms of the following free radicals.

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Acetonitrile (CH₃C≡N) is deprotonated by very strong bases. Write resonance forms to show the stabilization of the carbanion that results.

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3-Bromocyclohexene is a secondary halide. It undergoes S_N1 substitution about as fast as most tertiary halides. Use resonance structures to explain this enhanced reactivity.

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Benzyl bromide is a primary halide. It undergoes S_N1 substitution about as fast as most tertiary halides. Use resonance structures to explain this enhanced reactivity.

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Are the following pairs of structures resonance contributors or different compounds?

Textbook Question

Which of the following has delocalized electrons?

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