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Related Concept Videos

SN2 Reaction: Transition State02:26

SN2 Reaction: Transition State

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.
When the nucleophile approaches the electrophilic carbon with its lone pairs, the halide acts as a leaving group and moves away with the electron-pair bonded to the carbon. Dotted partial bonds represent the bonds being formed or broken...
SN2 Reaction: Kinetics02:14

SN2 Reaction: Kinetics

Kinetic Studies and Significance
In a chemical reaction, a relationship exists between the concentration of reactants and the rate at which the reaction proceeds. The study to measure this relationship is known as the kinetics of a chemical reaction. Kinetic studies are used to deduce the rate law of a chemical reaction, which provides information about the species involved during the transition state of the rate-determining step. Thus, kinetic studies help to derive the mechanism of a reaction.
SN1 Reaction: Mechanism02:25

SN1 Reaction: Mechanism

Kinetic studies of ionization of a tertiary halide in a protic solvent suggest that only the substrate participates in the rate-determining step (slow step). The nucleophile is involved only after the slowest step. The SN1 reaction takes place in a multiple-step mechanism. 
Firstly, the haloalkane ionizes to generate a carbocation intermediate and a halide ion. This heterolytic cleavage is highly endothermic with large activation energy. The ionization of the substrate, facilitated by a polar...
¹H NMR of Conformationally Flexible Molecules: Variable-Temperature NMR01:15

¹H NMR of Conformationally Flexible Molecules: Variable-Temperature NMR

The axial and equatorial protons in cyclohexane can be distinguished by performing a variable-temperature NMR experiment. In this process, except for one proton, the remaining eleven protons are replaced by deuterium. The deuterium substitution avoids the possible peak splitting caused by the spin-spin coupling between the adjacent protons. The remaining proton flips between the axial and equatorial positions.
SN2 Reaction: Mechanism02:27

SN2 Reaction: Mechanism

The kinetic studies of SN2 reactions suggest an essential feature of its mechanism: it is a single-step process without intermediates. Here, both the nucleophile and the substrate participate in the rate-determining step.
The presence of the more electronegative halogen in the substrate creates a polarized carbon-halide bond. The halide pulls the electron cloud generating an electrophilic center at the carbon atom. Thus, the carbon atom carries a partial positive charge while the halide has a...
Cycloaddition Reactions: MO Requirements for Thermal Activation01:16

Cycloaddition Reactions: MO Requirements for Thermal Activation

Thermal cycloadditions are reactions where the source of activation energy needed to initiate the reaction is provided in the form of heat. A typical example of a thermally-allowed cycloaddition is the Diels–Alder reaction, which is a [4 + 2] cycloaddition. In contrast, a [2 + 2] cycloaddition is thermally forbidden.

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Demonstrating the Simplicity and In Situ Temperature Monitoring of the Mechanochemical Synthesis of Metal Chalcogenides Suitable for Thermoelectrics
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Understanding the Mechanism of Low-Temperature NH3-SCR Half-Cycle on Cu-CHA Using Automated Reaction Path Search.

Ryusei Morimoto1, Kanami Sugiyama1,2, Masahiro Higashi3

  • 1Department of Molecular Engineering, Graduate School of Engineering, Kyoto University, Nishikyo-ku, Kyoto 615-8510, Japan.

The Journal of Physical Chemistry. A
|June 15, 2026
PubMed
Summary

Copper-exchanged chabazite (Cu-CHA) efficiently removes nitrogen oxides (NOx) via ammonia-assisted selective catalytic reduction. The rate-determining step involves intracomplex N-N bond formation, reducing Cu(II) to Cu(I).

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Magnetometric Characterization of Intermediates in the Solid-State Electrochemistry of Redox-Active Metal-Organic Frameworks

Published on: June 9, 2023

Area of Science:

  • Catalysis
  • Environmental Chemistry
  • Materials Science

Background:

  • Nitrogen oxides (NOx) from diesel engines are significant air pollutants.
  • Copper-exchanged chabazite (Cu-CHA) is effective for NOx removal via ammonia-assisted selective catalytic reduction (NH3-SCR).
  • The detailed molecular mechanism of Cu-CHA in NH3-SCR is not fully understood.

Purpose of the Study:

  • To elucidate the low-temperature NH3-SCR half-cycle mechanism on Cu-CHA.
  • To identify the rate-determining step and key intermediates in the NOx reduction process.
  • To understand the role of copper in facilitating the reaction.

Main Methods:

  • Density-functional theory (DFT) calculations were employed.
  • An automated reaction path search was integrated with DFT.
  • Analysis of reaction path networks, intermediates, and transition states was performed.

Main Results:

  • The reaction initiates with a side-on dimer [Cu2(II)O2(NH3)4]2+ reacting with NO.
  • N-N bond formation within a mononuclear complex, [CuII(NH3)2(O2N)]+, is the rate-determining step (ΔG‡ = 102.2 kJ/mol).
  • This step simultaneously reduces Cu(II) to Cu(I) and produces HONO and NH2NO.

Conclusions:

  • Intracomplex N-N bond formation is the crucial step in the low-temperature NH3-SCR half-cycle on Cu-CHA.
  • Copper's role in mediating ligand-ligand coupling is vital for N-N bond formation.
  • The findings provide molecular insights into NOx reduction over Cu-CHA catalysts.