Related Experiment Video
Updated: Mar 22, 2026
10:21
Developing Photosensitizer-Cobaloxime Hybrids for Solar-Driven H2 Production in Aqueous Aerobic Conditions
Published on: October 5, 2019
9.1K
Photoenolization of o-Methylvalerophenone Ester Derivative
Anushree Das1, Emily A Lao1, Anna D Gudmundsdottir1
1Department of Chemistry, University of Cincinnati, Cincinnati, OH.
Photochemistry and Photobiology
|April 11, 2016
Summary
Photolysis of ester 1 in oxygen-saturated methanol forms peroxide 2. Studies reveal biradical formation and subsequent photoenol generation, which revert to the original ester, indicating no further reaction pathways.
Area of Science:
- Photochemistry
- Organic Chemistry
- Reaction Mechanisms
Background:
- Understanding the photochemical behavior of esters is crucial for synthetic applications.
- Investigating reaction pathways under different atmospheric conditions provides insight into molecular transformations.
Purpose of the Study:
- To elucidate the photolysis mechanism of ester 1.
- To identify photoproducts and intermediates formed upon irradiation.
- To determine the fate of photoenols generated from ester 1.
Main Methods:
- Photolysis in argon- and oxygen-saturated solvents (methanol, acetonitrile).
- Laser flash photolysis to study transient intermediates.
- Density functional theory (DFT) calculations to analyze reaction barriers.
Main Results:
- Photolysis in argon yielded no products, while oxygen saturation produced peroxide 2.
- Intramolecular H atom abstraction formed biradical 3, which intersystem crossed to photoenols Z-4 and E-4.
- Photoenols 4 decayed primarily by regenerating ester 1.
Conclusions:
- The photoenol E-4 does not undergo spontaneous lactonization or electrocyclic ring closure.
- High transition state barriers prevent competing reactions, favoring regeneration of the starting ester.
Related Concept Videos
01:26Photochemical Electrocyclic Reactions: Stereochemistry
2.4K
The absorption of UV–visible light by conjugated systems causes the promotion of an electron from the ground state to the excited state. Consequently, photochemical electrocyclic reactions proceed via the excited-state HOMO rather than the ground-state HOMO. Since the ground- and excited-state HOMOs have different symmetries, the stereochemical outcome of electrocyclic reactions depends on the mode of activation; i.e., thermal or photochemical.
Selection Rules: Photochemical Activation
Selection Rules: Photochemical Activation
2.4K
01:12Stereochemical Effects of Enolization
2.8K
The chiral α-carbon of the carbonyl compound is the stereocenter of the molecule. As shown in the figure below, when such a carbonyl compound undergoes racemization under an acidic or basic condition, an achiral enol is formed.
2.8K
01:14Keto–Enol Tautomerism: Mechanism
8.2K
The keto and enol forms are known as tautomers and they constantly interconvert (or tautomerize) between the two forms under acid or base catalyzed conditions. Both the reactions involve the same steps—protonation and deprotonation— although in the reverse order.
8.2K
01:18Reactivity of Enols
4.3K
Enols are a class of compounds where a hydroxyl group is attached to a carbon–carbon double bond, which implies that it is a vinyl alcohol. A carbonyl compound with an α hydrogen undergoes keto–enol tautomerism and remains in equilibrium with its tautomer, the enol form. Usually, the keto tautomer is present in a higher concentration than the enol tautomer due to the higher bond energy of C=O compared to C=C. Moreover, the direction of the keto–enol equilibrium is...
4.3K
01:07Alkylation of β-Ketoester Enolates: Acetoacetic Ester Synthesis
4.8K
Acetoacetic ester synthesis is a method to obtain ketones from alkyl halides and β-keto esters. The reaction occurs in the presence of an alkoxide base that abstracts the acidic proton of the β-keto esters. The step results in an enolate ion which is doubly stabilized. The enolate then reacts with an alkyl halide via the SN2 process to produce an alkylated ester intermediate with a new C–C bond. The hydrolysis of the intermediate, followed by acidification, results in an...
4.8K
01:12Cycloaddition Reactions: MO Requirements for Photochemical Activation
2.8K
Some cycloaddition reactions are activated by heat, while others are initiated by light. For example, a [2 + 2] cycloaddition between two ethylene molecules occurs only in the presence of light. It is photochemically allowed but thermally forbidden.
2.8K