Textbook Question
The first amino acid in the pentapeptide of Figure 26.50, Pyr, is not one of the 20 amino acids in Table 26.1. Based on the following structure of Pyr, from which natural amino acid is it likely derived?
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Ch. 26 - Amino Acids, Proteins, and Peptide Synthesis
Mullins1st EditionOrganic Chemistry: A Learner Centered ApproachISBN: 9780137566471
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Table of contents
- Ch. 2 - General Chemistry Translated: Finding the Electrons114
- Ch. 3 - Alkanes and Cycloalkanes: Properties and Conformational Analysis109
- Ch. 4 - Acids and Bases: Electron Flow144
- Ch. 5 - Chemical Reaction Analysis: Thermodynamics and Kinetics118
- Ch. 6 - Stereoisomerism: Arrangement of Atoms in Space112
- Ch. 7 - Principles of Green (Organic) Chemistry3
- Ch. 8 - Alkenes I: Properties and Electrophilic Additions158
- Ch. 9 - Alkenes II: Oxidation and Reduction150
- Ch. 10 - Alkynes: Electrophilic Addition and Redox Reactions101
- Ch. 11 - Properties and Synthesis of Alkyl Halides: Radical Reactions108
- Ch. 12 - Substitution and Elimination: Reactions of Haloalkanes172
- Ch. 13 - Alcohols, Ethers and Related Compounds: Substitution and Elimination239
- Ch. 14 - Structural Identification I: Infrared Spectroscopy and Mass Spectrometry54
- Ch. 15 - Structural Identification II: Nuclear Magnetic Resonance Spectroscopy93
- Ch. 16 - Metals in Organic Chemistry48
- Ch. 17 - Carbonyl Addition Reactions: Aldehydes and Ketones45
- Ch. 18 - Nucleophilic Acyl Substitution I: Carboxylic Acids18
- Ch. 19 - Nucleophilic Acyl Substitution II: Carboxylic Acid Derivatives39
- Ch. 20 - Enolates: Carbonyl Addition and Substitution13
- Ch. 21 - Conjugated Systems I: Stability and Addition Reactions56
- Ch. 22 - Conjugated Systems II: Pericyclic Reactions54
- Ch. 23 - Benzene I: Aromatic Stability and Substitution Reactions64
- Ch. 24 - Benzene II: Reactions Influenced by the Aromatic Ring62
- Ch. 25 - Amines: Structure, Reactions, and Synthesis27
- Ch. 26 - Amino Acids, Proteins, and Peptide Synthesis9
- Ch. 27 - Carbohydrates, Nucleic Acids, and Lipids54
Mullins1st EditionOrganic Chemistry: A Learner Centered ApproachISBN: 9780137566471Not the one you use?Change textbook
Chapter 25, Problem 32
Why are conjugated molecules like the product of the ninhydrin reaction brightly colored?
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Conjugated molecules have alternating single and double bonds, which allow for the delocalization of π-electrons across the molecule. This delocalization lowers the energy gap between the ground state and the excited state of the electrons.
The energy required to excite an electron from the ground state to an excited state in conjugated systems is often in the visible region of the electromagnetic spectrum. This means that when these electrons absorb light, they do so in the visible range, which is why we perceive them as colored.
In the case of the ninhydrin reaction, the product formed is a conjugated system. The reaction typically involves the formation of a colored compound known as Ruhemann's purple, which is a result of the extended conjugation in the product.
The color intensity and specific hue depend on the extent of conjugation and the specific structure of the conjugated system. More extensive conjugation generally results in absorption of longer wavelengths of light, which can shift the color observed.
Understanding the relationship between conjugation and color can be useful in various applications, such as in the design of dyes and pigments, where specific colors are desired based on the molecular structure.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Conjugation in Organic Molecules
Conjugation occurs when p-orbitals overlap across adjacent single and multiple bonds, allowing for delocalization of electrons. This delocalization lowers the energy gap between molecular orbitals, which can affect the absorption of light and result in visible color. Conjugated systems are often more stable and can absorb specific wavelengths of light, leading to the appearance of color.
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Identifying organic molecules
Ninhydrin Reaction
The ninhydrin reaction is a chemical test used to detect amino acids and proteins. When ninhydrin reacts with amino acids, it forms a colored product, typically Ruhemann's purple. This reaction involves the formation of a conjugated system, which is responsible for the bright color observed. The color intensity can be used to quantify the presence of amino acids.
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Light Absorption and Color
The color of a compound is determined by the wavelengths of light it absorbs and reflects. Conjugated systems absorb light in the visible spectrum due to their lower energy gaps, which results in the emission of complementary colors. The specific color observed depends on the extent of conjugation and the specific wavelengths absorbed by the molecule.
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Related Practice
Textbook Question
Show how you would synthesize the following amino acids using the Strecker amino acid synthesis.
a. Ala
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Textbook Question
Draw the following amino acids in all possible protonation states as you move from high pH to low pH.
b. His
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Textbook Question
Although there is free rotation around most σ bonds, rotation is restricted around the C--N bond of an amide. Explain why this is true.
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Textbook Question
Provide a mechanism for the protection of the amine as the benzylcarbamate shown in Figure 26.33(a). <IMAGE>
Textbook Question
Provide a synthesis of the following amino acids using a combination of the HVZ and amination reactions.
b. Leu
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