Textbook Question
Give approximate wavenumbers for the major characteristic IR absorption bands that would be given by each of the following compounds:
e.
f.
1
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Ch. 13 - Mass Spectrometry; Infrared Spectroscopy; UV/Vis Spectroscopy
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. 13 - Mass Spectrometry; Infrared Spectroscopy; UV/Vis SpectroscopyProblem 70
Bruice 8th EditionCh. 13 - Mass Spectrometry; Infrared Spectroscopy; UV/Vis SpectroscopyProblem 70Chapter 14, Problem 70
Phenolphthalein is an acid–base indicator. In solutions of pH < 8.5, it is colorless; in solutions of pH > 8.5, it is deep red-purple. Account for the change in color.
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Phenolphthalein is a pH-sensitive compound that exists in different structural forms depending on the pH of the solution. These structural forms have different colors due to their distinct electronic configurations and absorption of light.
At a pH below 8.5, phenolphthalein exists predominantly in its protonated (acidic) form. This form does not absorb visible light in a way that produces color, so the solution appears colorless.
As the pH increases above 8.5, the solution becomes more basic, and phenolphthalein undergoes deprotonation. This deprotonation leads to the formation of a conjugated structure, which absorbs light in the visible spectrum, resulting in a red-purple color.
The transition from colorless to red-purple occurs because the deprotonated form of phenolphthalein has an extended conjugated π-electron system. This system lowers the energy gap between the ground and excited states, allowing the molecule to absorb light in the visible range.
The observed color change is a result of the equilibrium shift between the protonated (colorless) and deprotonated (red-purple) forms of phenolphthalein, which is influenced by the pH of the solution.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Acid-Base Indicators
Acid-base indicators are substances that change color in response to changes in pH. They are typically weak acids or bases that exhibit different colors in their protonated and deprotonated forms. Phenolphthalein, for example, is colorless in acidic solutions and turns deep red-purple in basic solutions, making it useful for determining the acidity or basicity of a solution.
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02:49
The Lewis definition of acids and bases.
pH Scale
The pH scale measures the acidity or basicity of a solution, ranging from 0 to 14. A pH of 7 is considered neutral, values below 7 indicate acidity, and values above 7 indicate basicity. The pH level affects the ionization of indicators like phenolphthalein, which is why its color changes at specific pH thresholds.
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02:15The pH scale vs. the pKa scale.
Ionization of Phenolphthalein
Phenolphthalein undergoes ionization depending on the pH of the solution. In acidic conditions (pH < 7), it remains in its protonated form, which is colorless. As the pH increases and the solution becomes basic (pH > 8.5), phenolphthalein loses protons and transitions to its deprotonated form, resulting in a deep red-purple color. This transition is what allows it to serve as an effective pH indicator.
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Related Practice
Textbook Question
Each of the IR spectra shown below is the spectrum of one of the following compounds. Identify the compound that produced each spectrum.
a. <IMAGE>
Textbook Question
How can you use UV spectroscopy to distinguish between the compounds in each of the following pairs?
a.
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Textbook Question
How can IR spectroscopy distinguish between 1-hexyne, 2-hexyne, and 3-hexyne?
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Textbook Question
Each of the IR spectra shown below is the spectrum of one of the following compounds. Identify the compound that produced each spectrum.
b. <IMAGE>
Textbook Question
Give approximate wavenumbers for the major characteristic IR absorption bands that would be given by each of the following compounds:
a.
b.
8
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