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Related Concept Videos

Cycloaddition Reactions: MO Requirements for Thermal Activation01:16

Cycloaddition Reactions: MO Requirements for Thermal Activation

4.1K
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.
4.1K
Electrophilic Addition of HX to 1,3-Butadiene: Thermodynamic vs Kinetic Control01:23

Electrophilic Addition of HX to 1,3-Butadiene: Thermodynamic vs Kinetic Control

3.4K
The addition of a hydrogen halide to 1,3-butadiene gives a mixture of 1,2- and 1,4-adducts. Since more substituted alkenes are more stable, the 1,4-adduct is expected to be the major product. However, the product distribution is strongly influenced by temperature; low temperature favors the 1,2-adduct, whereas the 1,4-adduct is predominant at high temperature.
3.4K
Thermal Electrocyclic Reactions: Stereochemistry01:17

Thermal Electrocyclic Reactions: Stereochemistry

2.5K
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.
2.5K
Regioselective Formation of Enolates01:33

Regioselective Formation of Enolates

3.3K
As depicted in the figure below, the unsymmetrical ketones can form two possible enolates:  less substituted or more substituted enolates. Usually, the thermodynamic enolates are formed from the more substituted α-carbon atom, while the kinetic enolates are formed faster by deprotonation from the less substituted position. The thermodynamic enolates have lower energy, so they are  more stable. But the energy required to form kinetic enolates is less.
3.3K
Thermal and Photochemical Electrocyclic Reactions: Overview01:26

Thermal and Photochemical Electrocyclic Reactions: Overview

2.9K
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.
2.9K
Thermal Sigmatropic Reactions: Overview01:16

Thermal Sigmatropic Reactions: Overview

2.4K
Sigmatropic rearrangements are a class of pericyclic reactions in which a σ bond migrates from one part of a π system to another. These are intramolecular rearrangements where the total number of σ and π bonds remain unchanged.
Sigmatropic shifts are classified based on an order term [i, j ], where i and j indicate the number of atoms across which each end of the σ bond migrates. Below are examples of a [3,3] sigmatropic shift in 1,5-hexadiene, referred...
2.4K

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Scale-up Chemical Synthesis of Thermally-activated Delayed Fluorescence Emitters Based on the Dibenzothiophene-S,S-Dioxide Core
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Substrate-Selective Temperature-Controlled Synthesis of Thiophene Derivatives at Interfaces.

Elena Pérez-Elvira1, Ana Barragán1, Diego J Vicent2

  • 1IMDEA Nanoscience, C/ Faraday 9, Campus De Cantoblanco, Madrid, 28049, Spain.

Angewandte Chemie (International Ed. in English)
|December 31, 2025
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Precise molecular transformations at interfaces depend on substrate and temperature. This study shows how organic molecule reactions vary on gold and silver surfaces, enabling tailored material properties.

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Area of Science:

  • Surface Science
  • Organic Chemistry
  • Materials Science

Background:

  • Controlling molecular transformations at interfaces is key for designing new materials.
  • Organic molecules can be engineered for specific properties through surface reactions.

Purpose of the Study:

  • Investigate substrate- and temperature-dependent reactions of a specific organic molecule (1) on Au(111) and Ag(111) surfaces.
  • Understand how different reaction conditions influence molecular self-assembly and transformations.

Main Methods:

  • Utilized scanning probe microscopy (SPM) and theoretical calculations.
  • Deposited bis(3,4-thiophene-fused)tetrabromo-p-benzoquinodimethane molecule (1) under ultra-high vacuum (UHV) conditions.
  • Controlled substrate temperatures during deposition and annealing.

Main Results:

  • At lower temperatures (RT to 100 °C), 1D covalent polymers form via debromination and homocoupling, assembling into 2D supramolecular polymers on both Au(111) and Ag(111).
  • At higher temperatures (≥175 °C), substrate-specific intramolecular reactions occur.
  • On Au(111), molecule 1 transforms into pentalenodithiophene and benzotrithiophene species.
  • On Ag(111), pentalenodithiophene formation is prevented.

Conclusions:

  • Molecular transformations at interfaces are highly sensitive to both substrate material and temperature.
  • Precise control over substrate selection and reaction temperature enables targeted synthesis of molecular structures and materials.
  • This work provides insights into designing functional organic materials through surface-mediated reactions.