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Videos de Conceptos Relacionados

Chair Conformation of Cyclohexane02:02

Chair Conformation of Cyclohexane

The chair conformation is the most stable form of cyclohexane due to the absence of angle and torsional strain. The absence of angle strain is a result of cyclohexane’s bond angle being very close to the ideal tetrahedral bond angle of 109.5° in its chair conformer. Similarly, the torsional strain is also absent owing to the perfectly staggered arrangement of bonds.
The hydrogen atoms linked to carbons are arranged in two different axial and equatorial orientations to achieve this staggered...
Stability of Substituted Cyclohexanes02:30

Stability of Substituted Cyclohexanes

This lesson discusses the stability of substituted cyclohexanes with a focus on energies of various conformers and the effect of 1,3-diaxial interactions.
The two chair conformations of cyclohexanes undergo rapid interconversion at room temperature. Both forms have identical energies and stabilities, each comprising equal amounts of the equilibrium mixture. Replacing a hydrogen atom with a functional group makes the two conformations energetically non-equivalent.
For example, in...
Conformations of Cyclohexane02:11

Conformations of Cyclohexane

Cyclohexane does not exist in a planar form due to the high angle and torsional strain it would experience in the planar structure. Instead, it adopts non-planar chair and boat conformations.
The chair form is the most stable and derives its name from its resemblance to the “easy chair.” In the chair conformation, two carbon atoms are arranged out-of-plane — one above and one below, minimizing the torsional strain. In the chair form, the bond angle is very close to the ideal tetrahedral value,...
Conformations of Cycloalkanes02:29

Conformations of Cycloalkanes

Adolf von Baeyer attempted to explain the instabilities of small and large cycloalkane rings using the concept of angle strain — the strain caused by the deviation of bond angles from the ideal 109.5° tetrahedral value for sp3  hybridized carbons. However, while cyclopropane and cyclobutane are strained, as expected from their highly compressed bond angles, cyclopentane is more strained than predicted, and cyclohexane is virtually strain-free. Hence, Baeyer’s theory that was based on the...
¹H NMR of Conformationally Flexible Molecules: Temporal Resolution00:52

¹H NMR of Conformationally Flexible Molecules: Temporal Resolution

At room temperature, the chair conformer of cyclohexane undergoes rapid ring flipping between two equivalent chair conformers at a rate of approximately 105 times per second. These two chair conformers are in equilibrium. The rapid ring flipping results in the interconversion of the axial proton to an equatorial proton and an equatorial to the axial proton. Such interconversions are too rapid and cannot be detected on the NMR timescale. Hence, the NMR spectrometer cannot distinguish between the...
Aromatic Hydrocarbon Cations: Structural Overview01:18

Aromatic Hydrocarbon Cations: Structural Overview

Cycloheptatriene is a neutral monocyclic unsaturated hydrocarbon that consists of an odd number of carbon atoms and an intervening sp3 carbon in the ring. The three double bonds in the ring correspond to 6 π electrons, which is a Huckel number, and therefore satisfies the criteria of 4n + 2 π electrons. However, the intervening sp3 carbon disrupts the continuous overlap of p orbitals. As a result, cycloheptatriene is not aromatic.
Removing one hydrogen from the intervening CH2 group with both...

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Preparation of a Corannulene-functionalized Hexahelicene by Copper(I)-catalyzed Alkyne-azide Cycloaddition of Nonplanar Polyaromatic Units
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Huéspedes macrocíclicos para los fullerenos: cambios extremos en las capacidades de unión con pequeñas variaciones

David Canevet1, María Gallego, Helena Isla

  • 1IMDEA-Nanociencia, Facultad de Ciencias, Ciudad Universitaria de Cantoblanco, E-28049 Madrid, Spain.

Journal of the American Chemical Society
|February 16, 2011
PubMed
Resumen

Los investigadores desarrollaron nuevos huéspedes macrocíclicos con unidades de tetratiafulvaleno extendido π (exTTF). Estos huéspedes exhiben afinidades de unión de récord mundial para los fullerenos C60, mostrando un reconocimiento molecular a medida.

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Área de la Ciencia:

  • Química supramolecular de las moléculas.
  • Química orgánica es la química orgánica.
  • Ciencia de los materiales Ciencia de los materiales.

Sus antecedentes:

  • Los fullerenos (C60) y C70) poseen propiedades electrónicas y estructurales únicas.
  • El desarrollo de moléculas selectivas y de alta afinidad para los fullerenos es un desafío significativo en el reconocimiento molecular.
  • Los derivados del tetratiofulvaleno extendido π (exTTF) ofrecen una complementariedad electrónica y de forma prometedora para la unión del fullereno.

Objetivo del estudio:

  • Para afinar los anfitriones macrocíclicos bis-exTTF para una mayor unión de los fullerenos C(60) y C(70).
  • Investigar el impacto de las variaciones estructurales en los espaciadores aromáticos y las longitudes de los enlaces en la complejación del fullereno.
  • Explorar las relaciones estructura-afinidad en una nueva familia de receptores de fullereno totalmente orgánicos.

Principales métodos:

  • Síntesis de nueve nuevos receptores macrocíclicos bis-exTTF con variados espaciadores aromáticos (p-xileno, m-xileno, 2,6-dimetilnaftaleno) y longitudes de enlace.
  • Utilizando la metatesis de cierre de anillo para la formación de macrociclos.
  • Titraciones UV-vis para evaluar cuantitativamente las afinidades de unión y estequiometrías con C60) y C70).
  • Modelado molecular preliminar para guiar el diseño estructural.

Principales resultados:

  • Se obtuvieron altas constantes de unión para la complejación C60, con log K a) de hasta 6,5 ± 0,5 en clorobenzeno, lo que representa un récord para los receptores totalmente orgánicos.
  • Se demostró que las modificaciones estructurales menores en los huéspedes macrocíclicos alteran significativamente la afinidad de unión y, en algunos casos, la estequiometría compleja.
  • Se identificaron características estructurales específicas que mejoran el reconocimiento de los fullerenos C60) y C70).

Conclusiones:

  • El estudio presenta una nueva familia de huéspedes macrocíclicos totalmente orgánicos altamente efectivos para los fullerenos.
  • Los resultados subrayan la importancia del control estructural preciso en la química huésped-huésped, particularmente para huéspedes desafiantes como los fullerenos.
  • La complementariedad electrónica y geométrica entre las unidades exTTF y los fullerenos es clave para la formación de complejos fuertes y estables observados.