The ring tension is an additional chemical binding energy that is stored in a ring-shaped molecule (e.g. cyclobutane ) made up of several atoms or has to be used beforehand for its ring closure. In most cases, the smaller the ring, the larger it is. They are caused by various stereochemical effects, especially the angular stress .
For alicyclic compounds , three and four-membered rings are very strained, since the strain-free tetrahedral angle of 109.5 ° is not achieved. Cyclopropane , which is flat due to its triangular structure, deviates the furthest from it with bond angles of 60 ° and therefore has the greatest ring tension.
Five-membered and six-membered rings (e.g .: cyclopentane , cyclohexane - cycloalkanes ) show little to no ring tension. The tetrahedron angle is maintained, which - as in the chain-like aliphatic compounds - leads to a conformation with a non-planar molecular structure. In terms of energy, they are therefore more favorable and arise preferentially (for example, the cyclic hemiacetal formation of carbohydrates ).
The opposite repulsion of substituents in the 1,5-position in cyclohexanes, n- pentane, etc., can lead to what is known as Newman stress , depending on whether they are in the equatorial or axial position .
Epoxides have very large hoop stresses due to their three-membered ring.
On the other hand, molecules with low ring tensions are energetically more favorable, so they are formed preferentially. In the case of aromatic ring molecules, such as benzene , the ring energies are negligible in relation to the mesomeric energy .
- Manussawee Hengsuwan, Ann-Christin Pöppler: Synthesis of five, six and seven rings . Georg-August University of Göttingen , 2007.
- Calculation and tabular representation of the ring strain in cycloalkanes at ChemGaroo , ChemgaPedia
- Representation of the conformation of normal cycloalkanes at the Friedrich-Alexander-Universität Erlangen-Nürnberg
- Cycloalkanes and stereoisomerism - ring tension and structure of the cycloalkanes ( Memento from February 5, 2010 in the Internet Archive ) at the Justus Liebig University in Giessen
- Essentials 4: Cycloalkanes (PDF; 128 kB) at Heinrich Heine University Düsseldorf
- Peptides and Proteins, page 10 (PDF; 2.8 MB) online-media.uni-marburg.de. Archived from the original on July 20, 2007. Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. Retrieved April 23, 2009.