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

12. Alcohols, Ethers, Epoxides and Thiols

Leaving Group Conversions - SOCl2 and PBr3

Organic Chemistry

12. Alcohols, Ethers, Epoxides and Thiols

Leaving Group Conversions - SOCl2 and PBr3

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Problem 36

Textbook Question

Besides PBr₃. and SOCl₂ , there are other ways of synthesizing haloalkanes. One such way is shown. Provide an arrow-pushing mechanism that rationalizes formation of the chloroalkane. [Hint: Dimethyl sulfide is a good nucleophile and Cl₂ is an electrophile. Start by reacting those two together.]

Verified step by step guidance

Begin by recognizing that dimethyl sulfide ((CH₃)₂S) acts as a nucleophile and chlorine (Cl₂) as an electrophile. The sulfur atom in dimethyl sulfide has a lone pair of electrons that can attack one of the chlorine atoms in Cl₂, forming a chlorosulfonium ion ((CH₃)₂SCl⁺) and a chloride ion (Cl⁻).

Next, consider the alcohol substrate, PhCH₂CH₂OH. The hydroxyl group (OH) is a poor leaving group, but it can be converted into a better leaving group by reacting with the chlorosulfonium ion. The lone pair on the oxygen of the alcohol attacks the sulfur atom in the chlorosulfonium ion, forming an intermediate where the oxygen is bonded to the sulfur.

This intermediate is unstable and will undergo a rearrangement. The chloride ion (Cl⁻) generated in the first step can now attack the carbon atom bonded to the oxygen, leading to the displacement of the dimethyl sulfoxide group ((CH₃)₂SO) and formation of the chloroalkane (PhCH₂CH₂Cl).

The dimethyl sulfoxide ((CH₃)₂SO) is formed as a byproduct, along with hydrochloric acid (HCl) from the protonation of the chloride ion by the hydrogen from the alcohol group.

Finally, ensure that all charges are balanced and the mechanism is consistent with the formation of the products shown in the image. The arrow-pushing should reflect the movement of electrons from nucleophiles to electrophiles, resulting in the formation of the chloroalkane and the byproducts.

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Key Concepts

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

Nucleophiles and Electrophiles

Nucleophiles are species that donate an electron pair to form a chemical bond, while electrophiles are electron-deficient species that accept an electron pair. In this reaction, dimethyl sulfide acts as a nucleophile, attacking the electrophilic chlorine molecule (Cl₂) to facilitate the substitution reaction that converts the alcohol to a chloroalkane.

Arrow-Pushing Mechanism

The arrow-pushing mechanism is a way to illustrate the movement of electrons during a chemical reaction. It shows how nucleophiles attack electrophiles and how bonds are formed or broken. In this case, arrows will depict the transfer of electrons from the nucleophile (dimethyl sulfide) to the electrophile (chlorine), leading to the formation of the chloroalkane.

Substitution Reactions

Substitution reactions involve the replacement of one functional group in a molecule with another. In this scenario, the hydroxyl group (-OH) of the alcohol is replaced by a chlorine atom, resulting in the formation of a chloroalkane. Understanding the mechanism of substitution is crucial for predicting the products of reactions involving haloalkanes.

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Related Practice

Textbook Question

Two products are observed in the following reaction.

a. Suggest a mechanism to explain how these two products are formed.

b. Your mechanism for part (a) should be different from the usual mechanism of the reaction of SOCl₂ with alcohols. Explain why the reaction follows a different mechanism in this case.

Textbook Question

Provide the alcohol that would be used to make the bromoalkanes shown using PBr₃.

(a)

Textbook Question

Provide the alcohol that would be used to make the bromoalkanes shown using PBr₃.

(b)

Textbook Question

Provide the alcohol that would be used to make the bromoalkanes shown using PBr₃.

(c)

Textbook Question

Identify the reagent that should be used to obtain each stereochemical outcome shown.

(a)

Textbook Question

Identify the reagent that should be used to obtain each stereochemical outcome shown.

(b)

Textbook Question

Predict the product(s) that would result when molecules (a)–(p) are allowed to react under the following conditions: (i) SOCl₂ ; (ii) PBr₃. If no reaction occurs, write 'no reaction.'

(a)

Textbook Question

Suggest the appropriate reagents to carry out the following transformations.

(g)

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