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Related Concept Videos

Directing Effect of Substituents: meta-Directing Groups01:09

Directing Effect of Substituents: meta-Directing Groups

5.2K
Substituents on the benzene ring that direct an incoming electrophile to undergo substitution at the meta position are called meta directors. All meta directors either have a positive charge on the atom directly bonded to the ring or a partial positive charge. These groups function by withdrawing electrons from the ring through inductive and resonance effects. Consider the carbocation intermediates formed upon the addition of an electrophile on nitrobenzene at the...
5.2K
meta-Directing Deactivators: –NO2, –CN, –CHO, –⁠CO2R, –COR, –CO2H01:13

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

6.0K
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...
6.0K
[3,3] Sigmatropic Rearrangement of 1,5-Dienes: Cope Rearrangement01:21

[3,3] Sigmatropic Rearrangement of 1,5-Dienes: Cope Rearrangement

3.0K
The Cope rearrangement is classified as a [3,3] sigmatropic shift in 1,5-dienes, leading to a more stable, isomeric 1,5-diene. The reaction involves a concerted movement of six electrons, four from two π bonds and two from a σ bond, via an energetically favorable chair-like transition state.
3.0K
Diazonium Group Substitution with Halogens and Cyanide: Sandmeyer and Schiemann Reactions01:20

Diazonium Group Substitution with Halogens and Cyanide: Sandmeyer and Schiemann Reactions

2.1K
Arenediazonium substitution reactions occur when the diazonium group is substituted by various functional groups such as halides, hydroxyl, nitrile, etc. For instance, arenediazonium salts react with copper(I) salts of chloride, bromide, or cyanide to form corresponding aryl chlorides, bromides, and nitriles. These reactions are named Sandmeyer reactions. Although the mechanism of this reaction is complicated, as illustrated in Figure 1, they are believed to progress via an aryl copper...
2.1K
¹H NMR Chemical Shift Equivalence: Homotopic and Heterotopic Protons01:03

¹H NMR Chemical Shift Equivalence: Homotopic and Heterotopic Protons

3.0K
Protons in identical electronic environments within a molecule are chemically equivalent and have the same chemical shift. The replacement test is a useful tool to identify chemical equivalence and predict NMR spectra. A substituent replaces each of the protons being examined and the resulting molecules are compared. If the same molecule is obtained, the protons are equivalent or homotopic. Replacement of any hydrogens in ethane by chlorine yields chloroethane because all six protons are...
3.0K
Diazonium Group Substitution: –OH and –H01:19

Diazonium Group Substitution: –OH and –H

3.0K
Nitrous acid, a weak acid, is prepared in situ via the reaction of sodium nitrite with a strong acid under cold conditions. This nitrous acid prepared in situ reacts with primary arylamines to form arenediazonium salts. Such reactions are known as diazotization reactions. As shown in Figure 1, the formation of arenediazonium salts begins with the decomposition of nitrous acid in an acidic solution to give nitrosonium ions.
3.0K

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Moving Dirac nodes by chemical substitution.

Niloufar Nilforoushan1, Michele Casula2, Adriano Amaricci3,4

  • 1Laboratoire de Physique des Solides, Université Paris-Saclay, CNRS, 91405 Orsay, France; niloufar.nilforoushan@phys.ens.fr michele.casula@upmc.fr marino.marsi@universite-paris-saclay.fr.

Proceedings of the National Academy of Sciences of the United States of America
|August 13, 2021
PubMed
Summary

Researchers tuned Dirac states in a transition metal sulfide via Co/Ni substitution. This doping controls Dirac line formation and metal-insulator transitions, offering a model for functionalizing Dirac materials.

Keywords:
Dirac semi-metalscorrelated electronic systemsfunctional topological materials

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Area of Science:

  • Condensed Matter Physics
  • Materials Science
  • Quantum Materials

Background:

  • Dirac fermions are crucial for topological phases, enabling exotic states like Weyl semimetals and topological insulators.
  • Controlling Dirac fermions is key for advancing electronic devices and quantum computation.

Purpose of the Study:

  • To investigate the tuning of Dirac states in a transition metal sulfide ([Formula: see text]) using Co/Ni substitution.
  • To explore the formation and manipulation of Dirac lines and their impact on material properties.

Main Methods:

  • Angle-Resolved Photo-Emission Spectroscopy (ARPES) experiments.
  • Ab initio simulations.
  • Chemical doping via Co/Ni substitution in [Formula: see text].

Main Results:

  • Successfully tuned Dirac states through Co/Ni substitution in [Formula: see text].
  • Observed the formation of Dirac lines with tunable position and shape in k-space.
  • Demonstrated that doping controls both Dirac band characteristics and the metal-insulator transition.

Conclusions:

  • [Formula: see text] serves as a model system for functionalizing Dirac materials.
  • Co/Ni substitution offers a pathway to engineer Dirac states and electron correlations.
  • The findings advance the understanding and application of topological materials.