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Related Concept Videos

Thermal and Photochemical Electrocyclic Reactions: Overview01:26

Thermal 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.
Thermal Electrocyclic Reactions: Stereochemistry01:17

Thermal 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.
Photochemical Electrocyclic Reactions: Stereochemistry01:26

Photochemical 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
Anionic Chain-Growth Polymerization: Overview01:20

Anionic Chain-Growth Polymerization: Overview

The polymerization process that involves carbanion as an intermediate is called anionic polymerization. It is also a type of addition or chain-growth polymerization. Anionic polymerization gets initiated by a strong nucleophile such as an organolithium or a Grignard reagent. The most commonly used initiator for anionic polymerization is butyl lithium. Monomers involved in anionic polymerization must possess a vinyl group bonded to one or two electron-withdrawing groups. For instance,...
Cationic Chain-Growth Polymerization: Mechanism00:57

Cationic Chain-Growth Polymerization: Mechanism

The cationic polymerization mechanism consists of three steps: initiation, propagation, and termination. In the initiation step of the polymerization process, the π bond of a monomer gets protonated by the Lewis acid catalyst, which is formed from boron trifluoride and water. The protonation of the π bond generates a carbocation stabilized by the electron‐donating group. In the propagation step, the π bond of the second monomer acts as a nucleophile and attacks the generated carbocation,...
Ion Exchange01:17

Ion Exchange

Ion exchange chromatography separates charged molecules from a solution by reversibly exchanging them with mobile, or 'active', ions associated with the oppositely charged stationary phase. This method can be used to separate ions, soften and deionize water, and purify solutions. The polymers comprising the ion-exchange column are high-molecular-weight and chemically stable polymers, crosslinked to be porous and essentially insoluble. They are also functionalized with either acidic or basic...

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Recent progress in polyaniline-based catalysts for electrochemical energy conversion.

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Area of Science:

  • Materials Science
  • Electrochemistry
  • Catalysis

Background:

  • Platinum (Pt) catalysts are effective but expensive for electrochemical energy conversion.
  • Noble metal-free electrocatalysts are urgently needed for widespread application.
  • Polyaniline (PANI) has emerged as a promising material for catalyst development.

Purpose of the Study:

  • To review the catalytic performance of PANI-based catalysts in various electrochemical reactions.
  • To highlight PANI's properties that enhance catalytic activity and stability.
  • To discuss strategies for improving PANI composite catalysts and identify future challenges.

Main Methods:

  • Literature review of PANI-based catalysts in electrochemical reactions.
  • Analysis of PANI's properties: redox activity, conductivity, stability, cost, and synthesis.
  • Discussion of catalytic mechanisms and strategies for performance enhancement.

Main Results:

  • PANI serves as an effective support, enhancing catalytic performance due to its unique properties.
  • PANI-based catalysts show potential in oxygen evolution (OER), hydrogen evolution (HER), oxygen reduction (ORR), and CO2 reduction (CO2RR).
  • Strategies include enhancing intrinsic activity of active sites and increasing active surface area.

Conclusions:

  • PANI is a versatile and cost-effective material for developing advanced electrocatalysts.
  • Further research is needed to address the limitations of PANI composite catalysts for specific reactions.
  • Optimizing PANI composites will be key for efficient electrochemical energy conversion.