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Related Concept Videos

Photochemical Electrocyclic Reactions: Stereochemistry01:26

Photochemical Electrocyclic Reactions: Stereochemistry

The absorption of UV–visible light by conjugated systems causes the promotion of an electron from the ground state to the excited state. Consequently, photochemical electrocyclic reactions proceed via the excited-state HOMO rather than the ground-state HOMO. Since the ground- and excited-state HOMOs have different symmetries, the stereochemical outcome of electrocyclic reactions depends on the mode of activation; i.e., thermal or photochemical.
Selection Rules: Photochemical Activation
Thermal and Photochemical Electrocyclic Reactions: Overview01:26

Thermal and Photochemical Electrocyclic Reactions: Overview

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.
Thermal Electrocyclic Reactions: Stereochemistry01:17

Thermal Electrocyclic Reactions: Stereochemistry

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.
π Electron Effects on Chemical Shift: Overview01:27

π Electron Effects on Chemical Shift: Overview

An applied magnetic field causes loosely bound π-electrons in organic molecules to circulate, producing a local or induced diamagnetic field over a large spatial volume. As the molecules tumble in solution, the field generated by π-electrons in spherical substituents results in a zero net field. However, the net field generated by π-electrons in non-spherical substituents is not zero. The effect of this induced field depends on the orientation of the molecule with respect to B0, resulting in...
π Electron Effects on Chemical Shift: Aromatic and Antiaromatic Compounds01:14

π Electron Effects on Chemical Shift: Aromatic and Antiaromatic Compounds

In aromatic compounds, such as benzene, the circulation of (4n + 2) π-electrons sets up a diamagnetic or diatropic ring current around the perimeter of the molecule. This current induces a magnetic field that opposes the external field inside the ring and reinforces it on the outside. The protons in benzene are deshielded and exhibit high chemical shifts in the range 6.5–8.5 ppm. The shielding effect at the center of the ring is evident in complex aromatic molecules, such as annulenes. In...
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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Hemicryptophane-assisted electron transfer: a structural and electronic study.

Olivier Perraud1, Jean-Bernard Tommasino, Vincent Robert

  • 1Laboratoire de Chimie, CNRS, Université Claude Bernard Lyon 1, École Normale Supérieure de Lyon, 46 Allée d'Italie, F-69364 Lyon, France.

Dalton Transactions (Cambridge, England : 2003)
|November 10, 2012
PubMed
Summary
This summary is machine-generated.

Three novel copper(II) complexes encapsulated in hemicryptophane cages were synthesized. The cage structure significantly influences the thermodynamics of electron transfer in these copper complexes.

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Area of Science:

  • Coordination Chemistry
  • Supramolecular Chemistry
  • Electrochemistry

Background:

  • Hemicryptophanes are macrocyclic ligands that can encapsulate metal ions.
  • Copper complexes are widely studied for their catalytic and redox properties.

Purpose of the Study:

  • To synthesize and characterize novel copper(II)@hemicryptophane complexes.
  • To investigate the influence of hemicryptophane cage structure on the redox properties of copper(II) complexes.

Main Methods:

  • Synthesis and characterization of three copper(II)@hemicryptophane complexes (Cu(II)@1, Cu(II)@2, Cu(II)@3).
  • Spectroscopic techniques: near-IR/vis and EPR spectroscopy.
  • Computational methods: Density Functional Theory (DFT) calculations.
  • Electrochemical studies: cyclic voltammetry and electrolysis coulometry in CH(2)Cl(2).

Main Results:

  • Spectroscopic and DFT data confirmed a trigonal-bipyramidal geometry for the N(4)Cu·H(2)O core.
  • Electrochemical studies revealed irreversible redox processes.
  • Electrolysis coulometry demonstrated the interconversion between Cu(II)/Cu(I) states.
  • The hemicryptophane cage structure was found to play a critical role in the thermodynamics of electron transfer.

Conclusions:

  • The synthesized copper(II)@hemicryptophane complexes exhibit unique structural and electrochemical properties.
  • The supramolecular environment provided by the hemicryptophane cage significantly impacts the electron transfer thermodynamics of the copper center.
  • These findings contribute to the understanding of host-guest interactions in redox-active systems.