Related Concept Videos
01:26Photochemical Electrocyclic Reactions: Stereochemistry
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
01:12Cycloaddition Reactions: MO Requirements for Photochemical Activation
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.
01:17Thermal Electrocyclic Reactions: Stereochemistry
The stereochemistry of electrocyclic reactions is strongly influenced by the orbital symmetry of the polyene HOMO. Under thermal conditions, the reaction proceeds via the ground-state HOMO.
Selection Rules: Thermal Activation
Conjugated systems containing an even number of π-electron pairs undergo a conrotatory ring closure. For example, thermal electrocyclization of (2E,4E)-2,4-hexadiene, a conjugated diene containing two π-electron pairs, gives trans-3,4-dimethylcyclobutene.
Selection Rules: Thermal Activation
Conjugated systems containing an even number of π-electron pairs undergo a conrotatory ring closure. For example, thermal electrocyclization of (2E,4E)-2,4-hexadiene, a conjugated diene containing two π-electron pairs, gives trans-3,4-dimethylcyclobutene.
02:35Electrophilic Addition to Alkynes: Hydrohalogenation
Electrophilic addition of hydrogen halides, HX (X = Cl, Br or I) to alkenes forms alkyl halides as per Markovnikov's rule, where the hydrogen gets added to the less substituted carbon of the double bond. Hydrohalogenation of alkynes takes place in a similar manner, with the first addition of HX forming a vinyl halide and the second giving a geminal dihalide.
02:44Oxidation of Alkenes: Syn Dihydroxylation with Osmium Tetraoxide
Alkenes are converted to 1,2-diols or glycols through a process called dihydroxylation. It involves the addition of two hydroxyl groups across the double bond with two different stereochemical approaches, namely anti and syn. Dihydroxylation using osmium tetroxide progresses with syn stereochemistry.
02:34Structural Isomerism
Isomerism in Complexes
Isomers are different chemical species that have the same chemical formula. Structural isomerism of coordination compounds can be divided into two subcategories, the linkage isomers and coordination-sphere isomers.
Linkage isomers occur when the coordination compound contains a ligand that can bind to the transition metal center through two different atoms. For example, the CN− ligand can bind through the carbon atom or through the nitrogen atom. Similarly, SCN− can be...
Isomers are different chemical species that have the same chemical formula. Structural isomerism of coordination compounds can be divided into two subcategories, the linkage isomers and coordination-sphere isomers.
Linkage isomers occur when the coordination compound contains a ligand that can bind to the transition metal center through two different atoms. For example, the CN− ligand can bind through the carbon atom or through the nitrogen atom. Similarly, SCN− can be...
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Updated: May 19, 2026
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Synthesis of Antiviral Tetrahydrocarbazole Derivatives by Photochemical and Acid-catalyzed C-H Functionalization via Intermediate Peroxides (CHIPS)
Published on: June 20, 2014
Organic Intercalation Enables Controllable Single-Atom Coordination for Efficient H2O2 Electrosynthesis.
Xingjian Sun1, Yijing Chen1, Weihu Zhang1
1State Key Laboratory of Materials-Oriented Chemical Engineering, Nanjing Tech University, Nanjing, China.
Angewandte Chemie (International Ed. in English)
|May 17, 2026
Summary
A new method uses organic intercalation to precisely control single-atom catalyst structures for efficient hydrogen peroxide (H₂O₂) production. This advance enables sustainable, on-site H₂O₂ synthesis with high selectivity and stability.
Area of Science:
- Electrochemistry
- Materials Science
- Catalysis
Background:
- Single-atom catalysts (SACs) are crucial for the two-electron oxygen reduction reaction (ORR) enabling sustainable hydrogen peroxide (H₂O₂) production.
- Current methods for heteroatom engineering in SACs involve complex multistep processes, hindering control over the coordination environment before pyrolysis.
Purpose of the Study:
- To develop a novel strategy for precise control over the first coordination sphere in SACs.
- To enable efficient and selective on-site H₂O₂ electrosynthesis through in situ coordination engineering.
Main Methods:
- An organic intercalation-driven precursor modulation strategy was employed to pre-organize coordinating atom sources.
- This method facilitates the preferential formation of a Cobalt-Nitrogen₃-Oxygen (Co-N₃O) coordination environment during pyrolysis.
- The strategy allows for in situ coordination engineering, offering an alternative to multi-step post-synthetic modifications.
Main Results:
- The developed Co-N₃O/C catalyst demonstrated high H₂O₂ selectivity (97.5%) and operational stability (120 hours at 100 mA cm⁻²).
- A 3.2 wt% H₂O₂ solution was accumulated under ambient-air-fed conditions.
- Analysis revealed that O incorporation in the Co-N₃O site modulates electronic structure and *OOH adsorption, favoring protonation over O-O bond cleavage.
Conclusions:
- The organic intercalation strategy provides a generalizable and controllable method for designing SACs with specific coordination environments.
- This approach offers significant potential for advancing industrial-scale H₂O₂ electrosynthesis through improved catalyst design and understanding.
- The findings provide key insights into coordination-mediated enhancements for ORR catalysis.