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Videos de Conceptos Relacionados

Halogens03:01

Halogens

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Group 17 elements, known as halogens, are nonmetals. At room temperature, fluorine and chlorine are gases, bromine is a liquid, and iodine a solid. Astatine is a highly unstable radioactive element, so currently, most of its properties are unknown due to its short half-life. Tennessine is a synthetic element also predicted to be in this group. 
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Energy Transfer in Chemical Reactions01:16

Energy Transfer in Chemical Reactions

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Chemical reactions require sufficient energy to cause the matter to collide with enough precision and force that old chemical bonds can be broken and new ones formed. In general, kinetic energy is the form of energy powering any type of matter in motion. Imagine a person building a brick wall. The energy it takes to lift and place one brick on top of another is the kinetic energy—the energy matter possesses because of its motion. Once the wall is in place, it stores potential energy.
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Regioselectivity of Electrophilic Additions-Peroxide Effect02:35

Regioselectivity of Electrophilic Additions-Peroxide Effect

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In the presence of organic peroxides, the addition of hydrogen bromide to an alkene yields the isomer that is not predicted by Markovnikov’s rule. For example, the addition of hydrogen bromide to 2-methylpropene in the presence of peroxides gives 1-bromo-2-methylpropane. This addition reaction proceeds via a free radical mechanism, which reverses the regioselectivity. The free radical reaction mechanism involves three stages: initiation, propagation, and termination.
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Regioselectivity and Stereochemistry of Hydroboration02:36

Regioselectivity and Stereochemistry of Hydroboration

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A significant aspect of hydroboration–oxidation is the regio- and stereochemical outcome of the reaction.
Hydroboration proceeds in a concerted fashion with the attack of borane on the π bond, giving a cyclic four-centered transition state. The –BH2 group is bonded to the less substituted carbon and –H to the more substituted carbon. The concerted nature requires the simultaneous addition of –H and –BH2 across the same face of the alkene giving syn stereochemistry.
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Regioselective Formation of Enolates01:33

Regioselective Formation of Enolates

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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.
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Ionization Energy03:12

Ionization Energy

43.2K
The amount of energy required to remove the most loosely bound electron from a gaseous atom in its ground state is called its first ionization energy (IE1). The first ionization energy for an element, X, is the energy required to form a cation with 1+ charge:
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Porfiroides expandidos regioselectivamente halogenados como bloques de construcción para la construcción de

Qizhao Li1, Chengjie Li1, Jinseok Kim2

  • 1Key Laboratory for Advanced Materials and Joint International Research Laboratory of Precision Chemistry and Molecular Engineering, Feringa Nobel Prize Scientist Joint Research Center, School of Chemistry and Molecular Engineering , East China University of Science & Technology , 130 Meilong Road , Shanghai 200237 , China.

Journal of the American Chemical Society
|March 10, 2019
PubMed
Resumen
Este resumen es generado por máquina.

Los investigadores sintetizaron porfirinas expandidas funcionalizadas regioselectivamente, creando nuevos porfirinos multicromóforos. Estos nuevos materiales exhiben una transferencia de energía eficiente, allanando el camino para aplicaciones optoelectrónicas avanzadas.

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Área de la Ciencia:

  • Química orgánica
  • Ciencias de los materiales
  • La fotoquímica

Sus antecedentes:

  • Las porfirinas expandidas poseen propiedades ópticas y electroquímicas únicas.
  • La funcionalización regioselectiva de las porfirinas expandidas es un desafío debido a los múltiples sitios reactivos.

Objetivo del estudio:

  • Para sintetizar isómeros halogenados regioselectivamente de isosmaragdirina neoconfusa.
  • Para construir porfirinoides multicromóforos utilizando estos bloques de construcción funcionales.
  • Investigar los mecanismos de transferencia de energía en las heterodiadas recién sintetizadas.

Principales métodos:

  • Halogenación de la isosmaragdirina neoconfundida (L5).
  • Las transformaciones de macrociclo a macrociclo.
  • Sonogashira reacciones de acoplamiento.
  • Espectroscopias de estado estacionario y de resolución temporal.
  • Los cálculos teóricos.

Principales resultados:

  • Síntesis de isómeros halogenados regioselectivos (L5-Br-A/B/C) de isosmaragdirina neoconfusa.
  • Construcción de las heterodiadas (L5-ZnP-A/B/C) que unen la porfirina de zinc con la isosmaragdirina en diferentes posiciones.
  • Elucidación de la cascada de energía altamente eficiente de la porfirina a la isosmaragdirina.
  • Demostración de los mecanismos de transferencia de energía dependientes del emplazamiento (transferencia de energía de resonancia por enlace y tipo Förster).

Conclusiones:

  • Se puede lograr la funcionalización selectiva del sitio de las porfirinas expandidas.
  • Las heterodiadas sintetizadas exhiben una transferencia de energía eficiente y dependiente del sitio.
  • Estos hallazgos ofrecen oportunidades para desarrollar nuevos materiales optoelectrónicos.