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

7. Substitution Reactions

Substitution Comparison

Organic Chemistry

7. Substitution Reactions

Substitution Comparison

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Problem 16

Textbook Question

Even with an excess of cyanide, only one equivalent will react with the following dibromoalkane. To which carbon will the cyanide add? Predict the product and explain your choice.

Verified step by step guidance

Analyze the structure of the dibromoalkane: The molecule contains two bromine atoms attached to different carbons. One bromine is attached to a secondary carbon (chiral center), and the other bromine is attached to a primary carbon.

Consider the reaction conditions: Sodium cyanide (NaCN) in DMSO is a nucleophilic substitution reaction (SN2 mechanism). The cyanide ion (CN⁻) is a strong nucleophile, and DMSO is a polar aprotic solvent that favors SN2 reactions.

Evaluate the reactivity of the two carbons: In an SN2 reaction, the nucleophile attacks the carbon attached to the leaving group (bromine) with the least steric hindrance. The primary carbon is less sterically hindered compared to the secondary carbon, making it the preferred site for nucleophilic attack.

Predict the product: The cyanide ion will replace the bromine atom on the primary carbon, forming a nitrile group (-C≡N) at that position. The secondary bromine will remain intact because only one equivalent of cyanide reacts.

Explain the choice: The preference for the primary carbon is due to the steric accessibility required for the SN2 mechanism. The secondary carbon is more hindered, making it less favorable for nucleophilic attack under these conditions.

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Key Concepts

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

Nucleophilic Substitution Reactions

Nucleophilic substitution reactions involve the replacement of a leaving group (like bromine) by a nucleophile (such as cyanide). The nucleophile attacks the electrophilic carbon atom bonded to the leaving group, leading to the formation of a new bond. Understanding the mechanism, whether it follows an SN1 or SN2 pathway, is crucial for predicting the product of the reaction.

Steric Hindrance

Steric hindrance refers to the repulsion between bulky groups in a molecule, which can affect the reactivity of certain sites. In this case, the presence of bulky groups near the bromine atoms can influence which carbon atom the cyanide will attack. The less hindered carbon is typically more accessible for nucleophilic attack, guiding the prediction of the product.

Reactivity of Alkyl Halides

Alkyl halides, such as dibromoalkanes, vary in reactivity based on the structure of the carbon atoms to which the halides are attached. Primary alkyl halides are generally more reactive towards nucleophiles than secondary or tertiary ones. In this scenario, recognizing the type of alkyl halide and the stability of the resulting carbocation (if applicable) is essential for predicting the outcome of the reaction.

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Related Practice

Textbook Question

Predict the product(s) of the following reactions.

(g)

Textbook Question

When trans-4-bromocyclohexanol is treated with base, an intramolecular substitution reaction occurs to give a cyclic ether. This product does not form when cis-4-bromocyclohexanol is reacted under the same conditions. Explain these observations.

Textbook Question

Which of the following reactions take place more rapidly when the concentration of the nucleophile is increased?

Textbook Question

Starting with (R)-1-deuterio-1-propanol, how could you prepare

c. (R)-1-deuterio-1-methoxypropane?

Textbook Question

Suggest a mechanism for the following reactions.

(a) Substitution:

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 ; (iii) SOCl₂ , NEt₃ (iv) 1. TsCl, Et₃N 2. NaCN; (v) 1. TsCl, Et₃N 2. NaOt-Bu (vi) H₂SO₄ (vii) HCl; (viii) HBr; (ix) PCC; (x) H₂CrO₄ , H₂O (xi) HOCl, H₂O (xii) HIO₄ If no reaction occurs, write 'no reaction.'

(o)

Textbook Question

Predict the product(s) that would result when molecules (a)–(p) are allowed to react under the following conditions: (iii) SOCl₂ , NEt₃ (iv) 1. TsCl, Et₃N 2. NaCN; If no reaction occurs, write 'no reaction.'

(o)

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.'

(k)

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