Helicene

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Helicene are a chemical group of substances derived from the term helix . The helicenes are aromatic compounds that are formally formed from phenanthrene (a planar molecule) through angled ortho - annulation . The number of condensed benzene rings varies. Helicenes with up to 16 fused benzene rings are known, ie [16] helicenes.

Chirality

  • ( P ) - (+) - Heptahelicene exhibits clockwise helicity .

  • ( M ) - (-) - Heptahelicene exhibits counter-clockwise helicity.

  • Spiral staircase in the Vatican Museum in Rome as an example of a helical structure for comparison. The symmetry corresponds to that of ( P ) -Heptahelicen

  • The screw rotation of this climbing plant corresponds to the direction of rotation of ( M ) -Heptahelicen

For space reasons, hexahelicene ([6] helicene, C 26 H 16 ) is already arranged in a helical manner. This helical arrangement of the benzene rings results in [6] helices, [7] helices (C 30 H 18 ), [8] helices (C 34 H 20 ), and [9] helices (C 38 H 22 ) etc. necessarily dissymmetry and thus are chiral aromatic hydrocarbons . These helical molecules have axial chirality , they form their own group within the structures with a chiral axis.

Racemic helicenes - e.g. B. the 1: 1 mixture of ( P ) - (+) - heptahelicene and ( M ) - (-) - heptahelicene - can be separated chromatographically on a chiral stationary phase.

Isomerism

In the helicenes, the benzene rings are 1,2- fused , but in the structurally isomeric acenes there is a 3,4-linkage of the benzene rings, so that a linear structure results.

Manufacturing

Using a synthesis induced by circularly polarized light, for example, (-) - [6] helicene can be synthesized in a targeted manner. The resolution of (±) - [6] helicene is also known.

The racemization of (-) - [6] helicene requires only a small amount of energy.

use

Despite their interesting chiral, physical, electronic and optical properties, helicenes were the subject of application-technical investigations only late. In the meantime, materials science , nanotechnology , biochemistry , liquid crystal research , polymer chemistry , supramolecular chemistry and preparative stereochemistry are looking for practically relevant areas of application for Helicene.

Individual evidence

  1. ↑ Bernhard Testa: Fundamentals of Organic Stereochemistry, Verlag Chemie, Weinheim, 1983 , pp. 65−68, ISBN 3-527-25935-X .
  2. ^ Marc Gingras: One hundred years of helicene chemistry. Part 1: non-stereoselective syntheses of carbohelicenes , Chem. Soc. Rev. 42 ( 2013 ) 968-1006.
  3. ^ RH Martin, M. Flammang-Barbieux, JP Cosyn, M. Gelbcke, Tetrahedron Letters 1968 , 3507.
  4. ^ A b Marc Gingras, Guy Félix and Romain Peresutti: One hundred years of helicene chemistry. Part 2: stereoselective syntheses and chiral separations of carbohelicenes , Chem. Soc. Rev. 42 ( 2013 ) 1007-1050.
  5. ↑ O. Buchardt, Angewandte Chemie , 86, 1974, 222-228.
  6. ↑ MS Newman and D. Lednicer, Journal of the American Chemical Society , 78, 1956 , 4765.
  7. ^ Marc Gingras: One hundred years of helicene chemistry. Part 3: applications and properties of carbohelicenes , Chem. Soc. Rev. 42 ( 2013 ) 1051-1095.
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