Textbook Question
Write the mechanism for the reaction of an amino acid with di-tert-butyl dicarbonate.
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Ch. 21 - Amino Acids, Peptides, and Proteins
Bruice8th EditionOrganic ChemistryISBN: 9780135213711
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Table of contents
- Ch. 1 - Remembering General Chemistry: Electronic Structure and Bonding (Part 1)31
- Ch. 1 - Remembering General Chemistry: Electronic Structure and Bonding (Part 2)65
- Ch. 2 - Acids and Bases: Central to Understanding Organic Chemistry84
- Ch. 3 - An Introduction to Organic Compounds:Nomenclature, Physical Properties, and Structure183
- Ch. 4 - Isomers: The Arrangement of Atoms in Space121
- Ch. 5 - Alkenes: Structure, Nomenclature, and an Introduction to Reactivity • Thermodynamics and Kinetics83
- Ch. 6 - The Reactions of Alkenes • The Stereochemistry of Addition Reactions175
- Ch. 7 - The Reactions of Alkynes • An Introduction to Multistep Synthesis119
- Ch. 8 - Delocalized Electrons: Their Effect on Stability, pKa, and the Products of a Reaction • Aromaticity and Electronic Effects: An Introduction to the Reactions of Benzene148
- Ch. 9 - Substitution and Elimination Reactions of Alkyl Halides212
- Ch. 10 - Reactions of Alcohols, Ethers, Epoxides, Amines, and Sulfur-Containing Compounds131
- Ch. 11 - Organometallic Compounds60
- Ch. 12 - Radicals90
- Ch. 13 - Mass Spectrometry; Infrared Spectroscopy; UV/Vis Spectroscopy62
- Ch. 14 - NMR Spectroscopy95
- Ch. 15 - Reactions of Carboxylic Acids and Carboxylic Acid Derivatives123
- Ch. 16 - Reactions of Aldehydes and Ketones • More Reactions of Carboxylic Acid Derivatives141
- Ch. 17 - Reactions at the Alpha-Carbon101
- Ch. 18 - Reactions of Benzene and Substituted Benzenes144
- Ch. 19 - More About Amines • Reactions of Heterocyclic Compounds49
- Ch. 20 - The Organic Chemistry of Carbohydrates80
- Ch. 21 - Amino Acids, Peptides, and Proteins57
- Ch. 22 - Catalysis in Organic Reactions and in Enzymatic Reactions35
- Ch. 23 - The Organic Chemistry of the Coenzymes—Compounds Derived from Vitamins1
- Ch. 28 - Pericyclic Reactions58
Chapter 22, Problem 71
Glycine has pKa values of 2.3 and 9.6. Do you expect the pKa values of glycylglycine to be higher or lower than these values?
Verified step by step guidance1
Understand the structure of glycylglycine: Glycylglycine is a dipeptide formed by two glycine molecules linked by a peptide bond. This structural change affects the ionizable groups compared to free glycine.
Identify the ionizable groups in glycylglycine: The molecule has an N-terminal amino group, a C-terminal carboxylic acid group, and an amide bond. The amide bond is not ionizable, but the amino and carboxylic acid groups are.
Compare the environment of the ionizable groups: In glycylglycine, the amino group is adjacent to the amide bond, and the carboxylic acid group is part of the peptide structure. These changes alter the electronic environment, which can influence the pKa values.
Predict the effect on the pKa of the carboxylic acid group: The electron-withdrawing effect of the amide bond stabilizes the conjugate base of the carboxylic acid, making it easier to lose a proton. This typically lowers the pKa of the carboxylic acid group compared to free glycine.
Predict the effect on the pKa of the amino group: The amide bond reduces the electron-donating ability of the amino group, making it less basic. This typically raises the pKa of the amino group compared to free glycine.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
pKa and Acid-Base Chemistry
pKa is a measure of the acidity of a compound, indicating the strength of an acid in solution. Lower pKa values correspond to stronger acids, while higher values indicate weaker acids. Understanding pKa is essential for predicting the protonation states of amino acids and peptides at different pH levels.
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07:45
Identifying pKa values
Amino Acid Structure and Properties
Amino acids, like glycine, contain both an amino group and a carboxyl group, allowing them to act as both acids and bases. The pKa values of these functional groups determine the ionization state of the amino acid at a given pH, which is crucial for understanding their behavior in biological systems and during peptide formation.
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04:10The 7 Ionizable Amino Acids
Peptide Bond Formation and Stability
Glycylglycine is a dipeptide formed from two glycine molecules. The formation of peptide bonds can influence the pKa values of the constituent amino acids due to changes in the electronic environment and steric factors. Generally, the pKa values of peptides can be affected by the neighboring amino acids, leading to shifts in acidity compared to the free amino acids.
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Related Practice
Textbook Question
α-Amino acids can be prepared by treating an aldehyde with ammonia/trace acid, followed by hydrogen cyanide, followed by acid-catalyzed hydrolysis.
a. Draw the structures of the two intermediates formed in this reaction.
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Textbook Question
α-Amino acids can be prepared by treating an aldehyde with ammonia/trace acid, followed by hydrogen cyanide, followed by acid-catalyzed hydrolysis.
b. What amino acid is formed when the aldehyde that is used is 3-methylbutanal?
c. What aldehyde is needed to prepare isoleucine?
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Textbook Question
Reaction of a polypeptide with carboxypeptidase A releases Met. The polypeptide undergoes partial hydrolysis to give the following peptides. What is the sequence of the polypeptide?
1. Ser, Lys, Trp
2. Gly, His, Ala
3. Glu, Val, Ser
4. Leu, Glu, Ser
5. Met, Ala, Gly
6. Ser, Lys, Val
7. Glu, His
8. Leu, Lys, Trp
9. Lys, Ser
10. Glu, His, Val
11. Trp, Leu, Glu
12. Ala, Met
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Textbook Question
Dithiothreitol reacts with disulfide bridges in the same way that 2-mercaptoethanol does. With dithiothreitol, however, the equilibrium lies much more to the right. Explain.
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Textbook Question
Show how valine can be prepared by
a. a Hell–Volhard–Zelinski reaction.