Auwers‐Skita Rule

Abstract

Auwers–Skita rule is an empirical rule related to the physical properties of geometrical isomers and their configurations. This rule has been extensively implemented during the assignment of the structures of isomers before the availability of NMR techniques. This rule has a wide application to assess the alicyclic epimers not differing in dipole moment, states that the isomer of smaller molecular volume and therefore higher physical constants has the higher heat content however, molecules of higher enthalpy have a lower melting point. It is also reported between the pair of cis ‐ and trans ‐ isomers, cis ‐compounds are higher in specific gravity and refractive index but smaller in molecular refraction. Between stereoisomers, the trans form of a pair of stereoisomers has the lower density, boiling point, and refractive index. This rule can even be used to assign the conformers, in which the conformer of higher enthalpy has a lower molecular volume. It has been found that such an empirical rule has limited reliability for complex systems, such as the configuration for isopinocampheol, 3‐methylcyclohexanol, thiabicyclo[3.3.0]‐octanes, and other 1,3‐disubstituted cyclohexenes.