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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6:43 minutes

Problem 39

Textbook Question

Chlorocyclohexane reacts with sodium cyanide (NaCN) in ethanol to give cyanocyclohexane. The rate of formation of cyanocyclohexane increases when a small amount of sodium iodide is added to the solution. Explain this acceleration in the rate.

Verified step by step guidance

Step 1: Recognize the type of reaction taking place. The reaction between chlorocyclohexane and sodium cyanide (NaCN) in ethanol is an example of an SN2 (bimolecular nucleophilic substitution) reaction. In this mechanism, the nucleophile (CN⁻) attacks the carbon bonded to the leaving group (Cl) in a single concerted step.

Step 2: Understand the role of the leaving group. The leaving group in this reaction is chloride (Cl⁻). The efficiency of an SN2 reaction depends significantly on the ability of the leaving group to depart. A better leaving group facilitates the reaction by stabilizing the negative charge after departure.

Step 3: Analyze the effect of sodium iodide (NaI). Sodium iodide dissociates in ethanol to produce iodide ions (I⁻). Iodide is a much better nucleophile and leaving group compared to chloride due to its larger size and ability to stabilize the negative charge. When iodide ions are present, they can replace the chloride ion on chlorocyclohexane via an SN2 reaction, forming iodo-cyclohexane as an intermediate.

Step 4: Explain the acceleration in the rate. The intermediate iodo-cyclohexane reacts with cyanide ions (CN⁻) much faster than chlorocyclohexane because iodide is a superior leaving group compared to chloride. This substitution process increases the overall rate of formation of cyanocyclohexane.

Step 5: Summarize the catalytic role of sodium iodide. Sodium iodide acts as a catalyst by facilitating the formation of iodo-cyclohexane, which accelerates the subsequent reaction with cyanide ions to produce cyanocyclohexane. This demonstrates how the presence of a better leaving group can enhance the rate of an SN2 reaction.

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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 in a molecule by a nucleophile. In this case, sodium cyanide acts as a nucleophile that attacks the carbon atom bonded to the chlorine in chlorocyclohexane, leading to the formation of cyanocyclohexane. Understanding the mechanism of these reactions, particularly whether they proceed via an SN1 or SN2 pathway, is crucial for analyzing reaction rates.

Role of Sodium Iodide

Sodium iodide can enhance the reaction rate by providing a better leaving group compared to chloride. The presence of iodide ions can facilitate the formation of a more reactive intermediate or transition state, thereby increasing the overall rate of the nucleophilic substitution. This phenomenon is often referred to as the 'iodide effect' in organic chemistry.

Solvent Effects on Reaction Rates

The choice of solvent can significantly influence the rate of chemical reactions. In this scenario, ethanol serves as a polar protic solvent, which can stabilize charged intermediates and transition states. The solvent's ability to solvate ions and facilitate nucleophilic attack is essential for understanding how the addition of sodium iodide accelerates the formation of cyanocyclohexane.

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What nucleophiles would form the following compounds as a result of reacting with 1-iodobutane?

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Aldolase shows no activity if it is incubated with iodoacetic acid before fructose-1,6-bisphosphate is added to the reaction mixture. What causes this loss of activity?

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Predict the major products of the following substitutions.

Textbook Question

Predict the major products of the following substitutions.

Textbook Question

Draw perspective structures or Fischer projections for the substitution products of the following reactions.

(b)

Textbook Question

a. Optically active 2-bromobutane undergoes racemization on treatment with a solution of KBr. Give a mechanism for this racemization.

b. In contrast, optically active butan-2-ol does not racemize on treatment with a solution of KOH. Explain why a reaction like that in part (a) does not occur.

Textbook Question

For each reaction, give the expected substitution product, and predict whether the mechanism will be predominantly first order (SN1) or second order (SN2).

c. 1-iodo-1-methylcyclohexane + ethanol

Textbook Question

The following reaction takes place under second-order conditions (strong nucleophile), yet the structure of the product shows rearrangement. Also, the rate of this reaction is several thousand times faster than the rate of substitution of hydroxide ion on 2-chlorobutane under similar conditions. Propose a mechanism to explain the enhanced rate and rearrangement observed in this unusual reaction. (“Et” is the abbreviation for ethyl.)

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