Related Experiment Video
Updated: May 10, 2026
![Cercosporin-Photocatalyzed [4+1]- and [4+2]-Annulations of Azoalkenes Under Mild Conditions](/_next/image?url=https%3A%2F%2Fcloudfront.jove.com%2FCDNSource%2Fteasers%2F60786.jpg&w=3840&q=50)
07:12
Cercosporin-Photocatalyzed [4+1]- and [4+2]-Annulations of Azoalkenes Under Mild Conditions
Published on: July 17, 2020
Anthrone and related hydroxyarenes: tautomerization and hydrogen bonding
Hans-Gert Korth1, Peter Mulder
1Institut für Organische Chemie, Universität Duisburg-Essen, D-45117 Essen, Germany. hans-gert.korth@uni-due.de
The Journal of Organic Chemistry
|July 3, 2013
Summary
Keto-enolization in hydroxyl-substituted naphthols and anthrols was studied. Intramolecular hydrogen bonds significantly shift tautomeric equilibrium towards enones, particularly in anthralin, suggesting potential antioxidant properties.
Area of Science:
- Computational Chemistry
- Physical Organic Chemistry
Background:
- Keto-enol tautomerism is a fundamental chemical process.
- Hydroxyl substitution influences tautomeric equilibria and hydrogen bonding.
Purpose of the Study:
- Investigate keto-enolization in hydroxyl-substituted naphthols and anthrols.
- Quantify tautomerization energetics and hydrogen bond effects.
- Assess potential antioxidant mechanisms.
Main Methods:
- Utilized CBS-QB3 computational calculations.
- Analyzed experimental and theoretical energetics for tautomeric equilibria.
- Quantified solvent effects and hydrogen bond enthalpies.
Main Results:
- Excellent agreement between theory and experiment for anthrone/anthrol equilibrium (Δ(t)H = 3.8 kcal mol⁻¹).
- 1-Naphthol favors the enol tautomer (Δ(t)H = -9.0 kcal mol⁻¹).
- Intramolecular hydrogen bonds in dihydroxy compounds shift equilibrium to enones (anthralin: Δ(t)H = 12.7 kcal mol⁻¹).
Conclusions:
- Hydroxyl substitution and intramolecular hydrogen bonding critically influence keto-enol tautomerism.
- Anthralin exhibits a strong preference for the enone form.
- Bond dissociation enthalpies suggest potential antioxidant activity, though the mechanism requires further elucidation.
Related Concept Videos
01:18Aromatic Hydrocarbon Cations: Structural Overview
Cycloheptatriene is a neutral monocyclic unsaturated hydrocarbon that consists of an odd number of carbon atoms and an intervening sp3 carbon in the ring. The three double bonds in the ring correspond to 6 π electrons, which is a Huckel number, and therefore satisfies the criteria of 4n + 2 π electrons. However, the intervening sp3 carbon disrupts the continuous overlap of p orbitals. As a result, cycloheptatriene is not aromatic.
Removing one hydrogen from the intervening CH2 group with both...
Removing one hydrogen from the intervening CH2 group with both...
02:40Alkynes to Aldehydes and Ketones: Acid-Catalyzed Hydration
Introduction
Analogous to alkenes, alkynes also undergo acid-catalyzed hydration. While the addition of water to an alkene gives an alcohol, hydration of alkynes produces different products such as aldehydes and ketones.
Analogous to alkenes, alkynes also undergo acid-catalyzed hydration. While the addition of water to an alkene gives an alcohol, hydration of alkynes produces different products such as aldehydes and ketones.
01:18Aromatic Hydrocarbon Anions: Structural Overview
Neutral hydrocarbons like cyclopentadiene with an odd number of carbon atoms and one intervening CH2 group in the ring are not aromatic. Cyclopentadiene with 4 π electrons does not satisfy the 4n + 2 π electron rule. Additionally, the intervening CH2 group is sp3 hybridized and lacks a vacant p orbital, thereby interrupting the overlap of p orbitals in a continuous manner and preventing the delocalization of π electrons throughout the ring.
Due to the absence of continuous overlap of p...
Due to the absence of continuous overlap of p...
02:47Alkynes to Aldehydes and Ketones: Hydroboration-Oxidation
Introduction
One of the convenient methods for the preparation of aldehydes and ketones is via hydration of alkynes. Hydroboration-oxidation of alkynes is an indirect hydration reaction in which an alkyne is treated with borane followed by oxidation with alkaline peroxide to form an enol that rapidly converts into an aldehyde or a ketone. Terminal alkynes form aldehydes, whereas internal alkynes give ketones as the final product.
One of the convenient methods for the preparation of aldehydes and ketones is via hydration of alkynes. Hydroboration-oxidation of alkynes is an indirect hydration reaction in which an alkyne is treated with borane followed by oxidation with alkaline peroxide to form an enol that rapidly converts into an aldehyde or a ketone. Terminal alkynes form aldehydes, whereas internal alkynes give ketones as the final product.
01:26Thermal and Photochemical Electrocyclic Reactions: Overview
Electrocyclic reactions are reversible reactions. They involve an intramolecular cyclization or ring-opening of a conjugated polyene. Shown below are two examples of electrocyclic reactions. In the first reaction, the formation of the cyclic product is favored. In contrast, in the second reaction, ring-opening is favored due to the high ring strain associated with cyclobutene formation.
02:38Electrophilic Addition to Alkynes: Halogenation
Introduction
Halogenation is another class of electrophilic addition reactions where a halogen molecule gets added across a π bond. In alkynes, the presence of two π bonds allows for the addition of two equivalents of halogens (bromine or chlorine). The addition of the first halogen molecule forms a trans-dihaloalkene as the major product and the cis isomer as the minor product. Subsequent addition of the second equivalent yields the tetrahalide.
Halogenation is another class of electrophilic addition reactions where a halogen molecule gets added across a π bond. In alkynes, the presence of two π bonds allows for the addition of two equivalents of halogens (bromine or chlorine). The addition of the first halogen molecule forms a trans-dihaloalkene as the major product and the cis isomer as the minor product. Subsequent addition of the second equivalent yields the tetrahalide.