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Related Concept Videos

Reduction of Alkynes to trans-Alkenes: Sodium in Liquid Ammonia02:10

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Alkynes can be reduced to trans-alkenes using sodium or lithium in liquid ammonia. The reaction, known as dissolving metal reduction, proceeds with an anti addition of hydrogen across the carbon–carbon triple bond to form the trans product. Since ammonia exists as a gas (bp = −33°C) at room temperature, the reaction is carried out at low temperatures using a mixture of dry ice (sublimes at −78°C) and acetone. 
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SN2 Reaction: Transition State02:26

SN2 Reaction: Transition State

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An SN2 reaction of an alkyl halide is a single-step process in which bond formation between the nucleophile and the substrate and bond breaking between the substrate and the halide occurs simultaneously through a transition state without forming an intermediate.
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Catalysis02:50

Catalysis

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The presence of a catalyst affects the rate of a chemical reaction. A catalyst is a substance that can increase the reaction rate without being consumed during the process. A basic comprehension of a catalysts’ role during chemical reactions can be understood from the concept of reaction mechanisms and energy diagrams.
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Radical Reactivity: Concentration Effects01:20

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In a radical reaction, the concentration of starting materials governs the selectivity of a radical. For example, the reaction between an alkyl halide and an alkene, in the presence of tin hydride and AIBN, begins with the generation of a tin radical. The generated radical then abstracts halogen from the alkyl halide, producing an alkyl radical. This alkyl radical can either react with tin hydride, yielding an alkane, or add to an alkene, generating a nitrile-stabilized radical, eventually...
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meta-Directing Deactivators: –NO2, –CN, –CHO, –⁠CO2R, –COR, –CO2H01:13

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All meta-directing substituents are deactivating groups. These substituents withdraw electrons from the aromatic ring, making the ring less reactive toward electrophilic substitution. For example, the nitration of nitrobenzene is 100,000 times slower than that of benzene because of the deactivating effect of the nitro group. The first step in an electrophilic aromatic substitution is the addition of an electrophile to form a resonance-stabilized carbocation. The energy diagrams for...
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Preparation of Amines: Alkylation of Ammonia and Amines01:30

Preparation of Amines: Alkylation of Ammonia and Amines

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Alkylation is one of the methods used to prepare amines. Direct alkylation of ammonia or a primary amine with an alkyl halide gives polyalkylated amines along with a quaternary ammonium salt through successive SN2 reactions. This process of making the quaternary salt through the direct alkylation method is called exhaustive alkylation.
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Orbital Engineering: Breaking the Activity-Selectivity-Stability Trilemma in Low-Temperature NH3-SCR over Single-Atom

Ting Zhang1, Jingnan Wang1, Jing Xia1

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Orbital engineering advances low-temperature catalysts for industrial denitrification. This framework optimizes activity, selectivity, and sulfur tolerance, overcoming key limitations in selective catalytic reduction with ammonia (NH3-SCR).

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Area of Science:

  • Catalysis
  • Materials Science
  • Quantum Chemistry

Background:

  • Selective catalytic reduction with ammonia (NH3-SCR) is vital for industrial denitrification.
  • Developing low-temperature catalysts (<250 °C) faces challenges in balancing activity, N2 selectivity, and poison resistance.

Purpose of the Study:

  • To resolve the catalyst trilemma by proposing an orbital engineering framework.
  • To decipher quantum-level interactions governing catalytic performance in NH3-SCR.

Main Methods:

  • Quantum-level analysis of spin states, orbital energetics, and electron occupancy.
  • Investigating the role of the lowest unoccupied molecular orbital (LUMO) energy.
  • Introducing spin-orientation tuning to enhance SO2 tolerance.

Main Results:

  • Elevating LUMO energy of active sites controls NH3-NO interactions, impacting activity and selectivity.
  • Spin-orientation tuning disrupts competitive adsorption, improving SO2 intolerance.
  • Synergistic design principles (support engineering, coordination modulation, etc.) concurrently optimize performance metrics.

Conclusions:

  • Orbital engineering provides a pathway to transcend limitations in low-temperature NH3-SCR catalysts.
  • This approach enables efficient denitrification under harsh conditions (low temperature, high sulfur, humidity).
  • The framework establishes a cornerstone for designing next-generation catalysts.