Textbook Question
Provide a mechanism for the formation of the hemiacetals shown. [Only (c) is favored as written.]
(a)
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Ch. 17 - Carbonyl Addition Reactions: Aldehydes and Ketones
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
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Mullins 1st EditionCh. 17 - Carbonyl Addition Reactions: Aldehydes and KetonesProblem 33a
Mullins 1st EditionCh. 17 - Carbonyl Addition Reactions: Aldehydes and KetonesProblem 33aChapter 16, Problem 33a
Which of the following cyclic hemiacetals would you expect to have the highest Keq for their formation? Explain your answer.
(a) 
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Identify the reactant and product in the given reaction. The reactant is a hydroxy aldehyde, and the product is a cyclic hemiacetal.
Understand that the formation of a cyclic hemiacetal involves the nucleophilic attack of the hydroxyl group on the carbonyl carbon, forming a new C-O bond and resulting in a ring structure.
Consider the size of the ring formed in the cyclic hemiacetal. Smaller rings, such as three-membered rings, are generally less stable due to angle strain.
Evaluate the stability of the cyclic hemiacetal. Five- and six-membered rings are typically more stable due to minimal angle strain and favorable enthalpic and entropic factors.
Conclude that the equilibrium constant (Keq) for the formation of a cyclic hemiacetal is higher when the resulting ring is more stable, typically favoring five- or six-membered rings over smaller rings.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Cyclic Hemiacetal Formation
Cyclic hemiacetals form when an alcohol group within a molecule reacts with an aldehyde or ketone group in the same molecule, creating a ring structure. This intramolecular reaction is favored when it results in a stable, five- or six-membered ring due to minimal ring strain and favorable enthalpic and entropic factors.
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Equilibrium Constant (K_eq)
The equilibrium constant (K_eq) for a reaction quantifies the ratio of the concentration of products to reactants at equilibrium. A higher K_eq indicates that the products are favored at equilibrium, suggesting that the formation of the cyclic hemiacetal is more thermodynamically favorable compared to its open-chain form.
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Ring Strain and Stability
Ring strain arises from bond angles deviating from their ideal values, torsional strain from eclipsing interactions, and steric strain from atoms being too close. Five- and six-membered rings are generally more stable due to minimal ring strain, making them more likely to form and persist, thus influencing the equilibrium position towards the cyclic form.
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Related Practice
Textbook Question
Show the product expected by the Wolff–Kishner reduction of the following aldehydes/ketones.
(a)
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Textbook Question
During an oxidation reaction, there must also be a reduction. What is reduced in the Pinnick oxidation?
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Textbook Question
Identify the hemiacetal functional group in each of the following molecules. These molecules may not be stable enough to be the favorable product in an equilibrium reaction.
(c)
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Textbook Question
Suggest the appropriate carbonyl and Wittig reagent to make the following alkenes.
a. (E)-7-methylnon-4-en-3-one
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Textbook Question
The following molecules were named incorrectly according to IUPAC nomenclature. Give the correct name of these compounds.
(a) 3-oxo-5-methylhexan-2-ol
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