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Related Concept Videos

meta-Directing Deactivators: –NO2, –CN, –CHO, –⁠CO2R, –COR, –CO2H01:13

meta-Directing Deactivators: –NO2, –CN, –CHO, –⁠CO2R, –COR, –CO2H

6.7K
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...
6.7K
2° Amines to N-Nitrosamines: Reaction with NaNO201:20

2° Amines to N-Nitrosamines: Reaction with NaNO2

5.4K
Secondary amines react with nitrous acid to form N-nitrosamines, as depicted in Figure 1. Nitrous acid, a weak and unstable acid, is formed in situ from an aqueous solution of sodium nitrite and strong acids, such as hydrochloric acid or sulfuric acid, in cold conditions. In the presence of an acid, the nitrous acid gets protonated. The subsequent loss of water results in the formation of the electrophile known as nitrosonium ion.
5.4K
SN2 Reaction: Kinetics02:14

SN2 Reaction: Kinetics

10.3K
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...
10.3K
SN2 Reaction: Mechanism02:27

SN2 Reaction: Mechanism

17.3K
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...
17.3K
SN2 Reaction: Transition State02:26

SN2 Reaction: Transition State

11.9K
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...
11.9K
SN2 Reaction: Stereochemistry02:23

SN2 Reaction: Stereochemistry

11.7K
In an SN2 reaction, the nucleophilic attack on the substrate and departure of the leaving group occurs simultaneously through a transition state. As the nucleophile approaches the substrate from the back-side, the configuration of the substrate carbon changes from tetrahedral to trigonal bipyramidal and then back to tetrahedral, leading to an inversion in the configuration of the product.
If the substrate is an achiral molecule at the α-carbon, the inversion of configuration is not...
11.7K

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Predicting Catalyst Extrudate Breakage Based on the Modulus of Rupture
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Predicting Catalyst Extrudate Breakage Based on the Modulus of Rupture

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Isoselective Lactide Ring Opening Polymerisation using [2]Rotaxane Catalysts.

Jason Y C Lim1,2, Nattawut Yuntawattana1, Paul D Beer1

  • 1Department of Chemistry, University of Oxford, Chemistry Research Laboratory, Mansfield Road, Oxford, OX1 3TA, UK.

Angewandte Chemie (International Ed. in English)
|March 13, 2019
PubMed
Summary
This summary is machine-generated.

Researchers developed a new method to control the tacticity of polylactide (PLA), a biodegradable plastic, using rotaxane conformational dynamism. This breakthrough enables high stereoselectivity in polymer synthesis without chiral additives, advancing circular economy plastics.

Keywords:
isoselectivitylactideorganocatalysisring-opening polymerisationrotaxane

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Area of Science:

  • Polymer Chemistry
  • Materials Science
  • Organic Chemistry

Background:

  • Polylactide (PLA) is a biodegradable and recyclable plastic crucial for the circular economy.
  • The thermal-mechanical properties of PLA are highly dependent on its stereochemistry, with isotactic PLA exhibiting superior performance.
  • Controlling PLA tacticity is essential for enhancing its material properties and expanding its applications.

Purpose of the Study:

  • To introduce a novel method for controlling the tacticity of polylactide during polymerization.
  • To investigate the use of rotaxane conformational dynamism for achieving high stereoselectivity.
  • To demonstrate a new approach for producing enhanced circular economy plastics.

Main Methods:

  • Utilizing dynamic achiral [2]rotaxanes to influence polymer tacticity.
  • Employing a chain-end control mechanism for polymerization.
  • Organocatalytic dynamic stereoselective polymerization.

Main Results:

  • Achieved high isoselectivity (Pi = 0.8 at 298 K) in PLA synthesis.
  • Demonstrated effective tacticity control without the need for chiral additives.
  • Established a rotaxane-based catalytic system for stereoselective polymerization.

Conclusions:

  • Rotaxane conformational dynamism offers a new pathway to control polymer tacticity.
  • This method provides a route to high-performance, stereochemically pure polylactide.
  • The organocatalytic dynamic stereoselectivity approach shows potential for broader applications in catalysis.