Textbook Question
At what pH is the concentration of a compound, with a pKa = 8.4, 100 times greater in its acidic form than in its basic form? At what pH is 50% of a compound, with a pKa = 7.3, in its basic form?
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Ch. 2 - Acids and Bases: Central to Understanding Organic Chemistry
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
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Bruice 8th EditionCh. 2 - Acids and Bases: Central to Understanding Organic ChemistryProblem 43c
Bruice 8th EditionCh. 2 - Acids and Bases: Central to Understanding Organic ChemistryProblem 43cChapter 3, Problem 43c
A naturally occurring amino acid such as alanine has a group that is a carboxylic acid and a group that is a protonated amine. The pKa values of the two groups are shown.
c. Draw the structure of alanine in a solution at physiological pH (pH 7.4).
Verified step by step guidance1
Step 1: Understand the structure of alanine. Alanine is an amino acid with a central alpha carbon bonded to a carboxylic acid group (-COOH), an amine group (-NH2), a hydrogen atom, and a methyl group (-CH3). At physiological pH (7.4), the carboxylic acid group and the amine group will exist in their ionized forms.
Step 2: Analyze the pKa values provided. The pKa of the carboxylic acid group is 2.32, meaning it will lose a proton and exist as a carboxylate ion (-COO⁻) at pH 7.4, which is above its pKa. The pKa of the amine group is 9.62, meaning it will remain protonated as -NH3⁺ at pH 7.4, which is below its pKa.
Step 3: Determine the ionization state of alanine at physiological pH. Since the pH is higher than the pKa of the carboxylic acid group, it will be deprotonated (-COO⁻). Since the pH is lower than the pKa of the amine group, it will remain protonated (-NH3⁺).
Step 4: Draw the structure of alanine at physiological pH. The alpha carbon will be bonded to the following groups: a carboxylate ion (-COO⁻), a protonated amine group (-NH3⁺), a hydrogen atom, and a methyl group (-CH3).
Step 5: Verify the zwitterionic nature of alanine at physiological pH. Alanine exists as a zwitterion, meaning it has both a positive charge (on the -NH3⁺ group) and a negative charge (on the -COO⁻ group) at pH 7.4.
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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 contains a central carbon atom bonded to an amino group (–NH2), a carboxylic acid group (–COOH), a hydrogen atom, and a variable side chain (R group). The properties of the side chain determine the characteristics of the amino acid, influencing protein structure and function.
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Standard Amino Acids
pKa and Acid-Base Chemistry
pKa is a measure of the strength of an acid in solution, indicating the pH at which half of the acid is dissociated. In the context of amino acids, the pKa values of the carboxylic acid and the protonated amine groups help determine their ionization states at a given pH. At physiological pH (7.4), the carboxylic acid group is typically deprotonated, while the amine group remains protonated, influencing the overall charge of the amino acid.
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Zwitterion Formation
A zwitterion is a molecule that has both positive and negative charges but is overall neutral. In amino acids like alanine at physiological pH, the carboxylic acid group loses a proton (–COO⁻), while the amino group retains a proton (–NH₃⁺). This results in a zwitterionic form, which is crucial for the solubility and reactivity of amino acids in biological systems.
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Related Practice
Textbook Question
A naturally occurring amino acid such as alanine has a group that is a carboxylic acid and a group that is a protonated amine. The pKa values of the two groups are shown.
d. Draw the structure of alanine in a solution at pH = 12.
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Textbook Question
A naturally occurring amino acid such as alanine has a group that is a carboxylic acid and a group that is a protonated amine. The pKa values of the two groups are shown.
e. Is there a pH at which alanine is uncharged (that is, neither group has a charge)?
f. At what pH does alanine have no net charge (that is, the amount of negative charge is the same as the amount of positive charge)?
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Textbook Question
Indicate whether an alcohol (ROH) with a pKa value of 15 has more charged or more neutral molecules in a solution with the pH values given in Problem 41.
3. pH = 7
4. pH = 10
5. pH = 13
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Textbook Question
Indicate whether an alcohol (ROH) with a pKa value of 15 has more charged or more neutral molecules in a solution with the pH values given in Problem 41.
1. pH = 1
2. pH = 3
3. pH = 5
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Textbook Question
Indicate whether a protonated amine (RN+H3) with a pKa value of 9 has more charged or more neutral molecules in a solution with the pH values given in Problem 41.
1. pH = 1
2. pH = 3
3. pH = 5
4. pH = 7
5. pH = 10
6. pH = 13
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