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At pH = 7, one of the ions shown here is purple and the other is blue. Which is which?
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Ch. 13 - Mass Spectrometry; Infrared Spectroscopy; UV/Vis Spectroscopy
Bruice8th EditionOrganic ChemistryISBN: 9780135213711
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TOC.tableOfContents
- Ch. 1 - Remembering General Chemistry: Electronic Structure and Bonding31
- 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 SpectroscopyProblema 36
Bruice 8th EditionCh. 13 - Mass Spectrometry; Infrared Spectroscopy; UV/Vis SpectroscopyProblema 36Capitolo 13, Problema 36
Predict the λmax of the following compound:
Guida verificata passo dopo passo1
Step 1: Understand the concept of λmax (maximum wavelength of absorption). λmax is influenced by conjugation in the molecule. The more conjugated double bonds present, the higher the λmax value due to the stabilization of the π-electron system.
Step 2: Analyze the given compounds. The first compound, but-3-en-2-one, has one conjugated double bond and a λmax of 219 nm. The second compound, (E)-hexa-3,5-dien-2-one, has two conjugated double bonds and a λmax of 249 nm. The third compound, cyclopent-2-enone, has one conjugated double bond but is part of a cyclic structure.
Step 3: Consider the effect of the cyclic structure in cyclopent-2-enone. Cyclic conjugated systems can have slightly different λmax values compared to acyclic systems due to ring strain and orbital overlap. Cyclopent-2-enone is expected to have a λmax slightly higher than but-3-en-2-one due to the stabilization provided by the cyclic structure.
Step 4: Use the base λmax value for an α,β-unsaturated ketone (approximately 215 nm) and add any increments for structural features. For example, cyclic conjugation may add a small increment to the λmax value.
Step 5: Predict the λmax for cyclopent-2-enone based on the trends observed in the other compounds and the structural features of the molecule. Compare it to the λmax values of but-3-en-2-one and (E)-hexa-3,5-dien-2-one to make an educated estimate.
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Conjugation
Conjugation refers to the overlap of p-orbitals across adjacent double bonds or between double bonds and lone pairs, allowing for delocalization of electrons. This delocalization lowers the energy of the molecule and can lead to increased stability and shifts in the absorption spectrum, affecting the λmax value. Compounds with extended conjugation typically absorb light at longer wavelengths.
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Conjugated states
λmax (Lambda Max)
λmax is the wavelength at which a compound exhibits maximum absorbance in UV-Vis spectroscopy. It is influenced by the electronic structure of the molecule, particularly the presence of conjugated systems. Understanding λmax is crucial for predicting how different structural features, such as double bonds and functional groups, affect a compound's light absorption properties.
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Percorso guidato
1:44The UV-Vis Spectroscopy Concept 3
Structural Effects on Absorption
The structure of a molecule significantly impacts its electronic transitions and, consequently, its λmax. Factors such as the number of conjugated double bonds, steric hindrance, and the presence of electron-withdrawing or donating groups can alter the energy levels of the molecular orbitals. Analyzing these structural features helps predict the λmax for compounds like cyclopent-2-en-one based on known values of similar structures.
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2:02Directing Effects in Substituted Pyrroles, Furans, and Thiophenes Concept 1
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