Auwers-Skita rule
The Auwers-Skita rule is historically interesting in chemistry , but has largely been forgotten today due to alternative physical-chemical measurements ( spectroscopy ), named after Karl Friedrich von Auwers (1863–1939) and Aladar Skita (1876–1953) .
The Auwers-Skita rule is an empirical rule about the relationship between the physical properties of cis - trans -isomeric compounds and their spatial structure.
The rule is applicable to many epimers that do not differ in the dipole moment . Accordingly, the isomer with a smaller molecular volume has higher physical constants. Molecules of higher enthalpy have a lower melting point . In the case of cis and trans isomers, the cis compound accordingly has a higher density and a higher refractive index . The trans form of a cis - trans stereoisomer pair has a lower density, a lower boiling point and a lower refractive index. The Auwers – Skita rule can also be applied to conformers . The higher enthalpy conformer has a smaller molecular volume.
In a variant modified by H. van Bekkum, the Auwers-Skita rule is a useful means of determining the configuration of cis and trans isomeric amines in addition to modern analytical methods .
Individual evidence
- ↑ Herbert Feltkamp, Klaus Dieter Thomas: Application of the Auwers-Skita rule to stereoisomeric amines , Liebigs Annalen der Chemie 685 (1965) 148-154, doi : 10.1002 / jlac . 19656850118 .