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

29. Amino Acids

Proteins and Amino Acids

Organic Chemistry

29. Amino Acids

Proteins and Amino Acids

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Problem 20

Textbook Question

Why is excess ammonia used in the preceding reaction?

Verified step by step guidance

Ammonia (NH₃) is a nucleophile, meaning it donates a pair of electrons to form a bond with an electrophile. In the reaction, ammonia is used to attack the electrophilic center, typically a carbon atom in a substrate like an alkyl halide or acyl compound.

Excess ammonia is used to drive the reaction toward the formation of the desired product. This is based on Le Chatelier's principle, which states that increasing the concentration of a reactant (in this case, ammonia) will shift the equilibrium toward the product side.

Using excess ammonia minimizes the likelihood of side reactions. For example, in reactions involving alkyl halides, excess ammonia helps prevent the formation of secondary or tertiary amines by limiting the availability of the alkyl halide for further substitution reactions.

Excess ammonia also ensures that the reaction proceeds to completion by maintaining a high concentration of the nucleophile, which increases the reaction rate and the yield of the desired product.

Finally, excess ammonia can act as a solvent in some cases, providing a medium for the reaction to occur and ensuring that all reactants are well-dissolved and able to interact effectively.

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Key Concepts

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

Le Chatelier's Principle

Le Chatelier's Principle states that if a system at equilibrium is disturbed, the system will adjust to counteract the disturbance and restore a new equilibrium. In the context of reactions involving ammonia, using excess ammonia can shift the equilibrium position towards the products, enhancing the yield of the desired product.

Ammonia as a Nucleophile

Ammonia (NH3) acts as a nucleophile due to the presence of a lone pair of electrons on the nitrogen atom. This property allows ammonia to attack electrophilic centers in organic molecules, facilitating various reactions, such as nucleophilic substitutions or additions, which are often key in organic synthesis.

Reaction Yield and Selectivity

In organic chemistry, the yield of a reaction refers to the amount of product formed relative to the theoretical maximum. Using excess reagents, like ammonia, can improve both the yield and selectivity of a reaction by ensuring that the limiting reactant is fully consumed, thus driving the reaction to completion and minimizing by-products.

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Related Practice

Textbook Question

Indicate the peptides produced from cleavage by the indicated reagent:

a. His-Lys-Leu-Val-Glu-Pro-Arg-Ala-Gly-Ala by trypsin

b. Leu-Gly-Ser-Met-Phe-Pro-Tyr-Gly-Val by chymotrypsin

Textbook Question

A decapeptide undergoes partial hydrolysis to give peptides whose amino acid compositions are shown. Reaction of the intact decapeptide with Edman's reagent releases PTH-Gly. What is the sequence of the decapeptide?

1. Ala, Trp

2. Val, Pro, Asp

3. Pro, Val

4. Ala, Glu

5. Trp, Ala, Arg

6. Arg, Gly

7. Glu, Ala, Leu

8. Met, Pro, Leu, Glu

Textbook Question

Which bonds in the backbone of a peptide can rotate freely?

Textbook Question

Show the steps in the synthesis of the tetrapeptide in Problem 34, using Merrifield's method.