Textbook Question
Explain the difference in the pKa values of the carboxyl groups of alanine, serine, and cysteine
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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 57b,c
What aldehydes are formed when the following amino acids are treated with ninhydrin?
b. leucine
c. arginine
Verified step by step guidance1
Understand the reaction: Ninhydrin reacts with amino acids to produce aldehydes, carbon dioxide, and ammonia. The aldehyde formed depends on the structure of the amino acid's side chain.
For leucine: Identify the structure of leucine. It has an isobutyl side chain (-CH2-CH(CH3)2). When treated with ninhydrin, the amino group is removed, and the side chain is converted into an aldehyde. The resulting aldehyde will have the structure of the side chain minus the terminal carbon.
For arginine: Identify the structure of arginine. It has a guanidino group (-C(NH2)2-NH) attached to a 3-carbon chain. When treated with ninhydrin, the guanidino group is removed, and the aldehyde formed will correspond to the 3-carbon chain.
Write the general reaction mechanism: Ninhydrin reacts with the amino group of the amino acid, forming a Schiff base intermediate. This intermediate undergoes decarboxylation and hydrolysis to yield the aldehyde.
Determine the specific aldehydes: For leucine, the aldehyde will be isobutyraldehyde (CH3-CH2-CHO). For arginine, the aldehyde will be 3-aminopropanal (H2N-CH2-CH2-CHO).
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Amino Acids
Amino acids are organic compounds that serve as the building blocks of proteins. Each amino acid has a central carbon atom bonded to an amino group, a carboxyl group, a hydrogen atom, and a variable side chain (R group) that determines its unique properties. Understanding the structure and properties of specific amino acids, such as leucine and arginine, is essential for predicting the products formed during chemical reactions.
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Standard Amino Acids
Ninhydrin Reaction
The ninhydrin reaction is a chemical test used to detect amino acids and proteins. When amino acids react with ninhydrin, they undergo a dehydration reaction, resulting in the formation of a colored complex, typically a purple-blue hue. This reaction not only confirms the presence of amino acids but also leads to the formation of aldehydes, which are important for identifying the specific amino acids involved.
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Aldehyde Formation
Aldehydes are organic compounds characterized by the presence of a carbonyl group (C=O) bonded to at least one hydrogen atom. In the context of the ninhydrin reaction, the amino acids leucine and arginine are converted into their corresponding aldehydes upon treatment with ninhydrin. Recognizing the specific aldehydes formed from these amino acids is crucial for understanding the outcomes of the reaction and the identification of the amino acids.
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Related Practice
Textbook Question
Identify the location and type of charge on the hexapeptide Lys-Ser-Asp-Cys-His-Tyr at each of the following pH values:
c. pH=7
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Textbook Question
Explain why amino acids, unlike most amines and carboxylic acids, are insoluble in diethyl ether.
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Textbook Question
Which has a higher percentage of negative charge at physiological pH (7.4), leucine with pI = 5.98 or asparagine with pI = 5.43?
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Textbook Question
Draw the form of aspartate that predominates at the following pH values:
d. pH=11.0
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Textbook Question
Draw the form of aspartate that predominates at the following pH values: c. pH=6.0
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